Cubic Diamond Hexagonal Lonsdaleite By Shock Compression

by Tommy on 21/10/2016

With this PETM result, even though the shards are largish, I was thinking about nanodiamods.

Nanosecond formation of diamond and lonsdaleite by shock compression of graphite, D. Kraus, A. Ravasio, M. Gauthier, D. O. Gericke, J. Vorberger, S. Frydrych, J. Helfrich, L. B. Fletcher, G. Schaumann, B. Nagler, B. Barbrel, B. Bachmann, E. J. Gamboa, S. Göde, E. Granados, G. Gregori, H. J. Lee, P. Neumayer, W. Schumaker, T. Döppner, R. W. Falcone, S. H. Glenzer and M. Roth, Nature Communications, 7, 10970 (14 March 2016), doi:10.1038/ncomms10970

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.

Lonsdaleite is a real survivor!

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Elon Musk and Tesla to Announce the Obvious Thing Tonight

by Tommy on 19/10/2016

The obvious thing being interfacing the car batteries with the house batteries.

And the house solar panels of course.

But I could be wrong.

Update: That feature seems more like a Solar City announcement, so with this announcement I’m going with integrated solar panels on the roof and the hood of the Tesla Model 3. Why not?

An obvious no brainer that should have been done decades ago to all conventional vehicles.

Update 2: Ok, ejection seats! That could work. Rockets have them, right?

Update 3: There does not seem to be any link to this.

Update 4: Self driving cars. I want flying cars!

And floating cities with moving sidewalks.

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Are Black Holes Preferentially Sucking in Dark Matter?

by Tommy on 19/10/2016
Cosmic Dark Matter Black Hole Baryon String Void Structure

Cosmic Dark Matter Black Hole Baryon String Void Structure

I have been entertaining lots of conceptual dark matter cosmic evolution scenarios lately.

This is just one of many. Lots O’fun it is.

But not very productive as of yet.

Too many possibilities.

So much spacetime.

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Pressure Induced Superconductivity of Bismuth Telluride Iodide BeTeI

by Tommy on 19/10/2016

I’ve been keeping an eye on this for a while.

Topological quantum phase transition and superconductivity induced by pressure in the bismuth tellurohalide BiTeI, Yanpeng Qi, Wujun Shi, Pavel G. Naumov, Nitesh Kumar, Raman Sankar, Walter Schnelle, Chandra Shekhar, F. C. Chou, Claudia Felser, Binghai Yan and Sergey A. Medvedev (17 October 2016)

A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor BiTeI with giant Rashba spin splitting. In this work, the evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr while the resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that the superconductivity may develop from the multi-valley semiconductor phase. The superconducting transition temperature Tc increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. Our results demonstrate that BiTeX (X = I, Br) compounds with non-trivial topology of electronic states display new ground states upon compression.

See also:

Pressure dependence of the band-gap energy in BiTeI, Sümeyra Güler-Kılıç and Çetin Kılıç, Phys. Rev. B, 94, 165203 (13 October 2016), DOI:10.1103/PhysRevB.94.165203

The evolution of the electronic structure of BiTeI, a layered semiconductor with a van der Waals gap, under compression is studied by employing semilocal and dispersion-corrected density-functional calculations. Comparative analysis of the results of these calculations shows that the band-gap energy of BiTeI decreases till it attains a minimum value of zero at a critical pressure, after which it increases again. The critical pressure corresponding to the closure of the band gap is calculated, at which BiTeI becomes a topological insulator. Comparison of the critical pressure to the pressure at which BiTeI undergoes a structural phase transition indicates that the closure of the band gap would not be hindered by a structural transformation. Moreover, the band-gap pressure coefficients of BiTeI are computed, and an expression of the critical pressure is devised in terms of these coefficients. Our findings indicate that the semilocal and dispersion-corrected approaches are in conflict about the compressibility of BiTeI, which result in overestimation and underestimation, respectively. Nevertheless, the effect of pressure on the atomic structure of BiTeI is found to be manifested primarily as the reduction of the width of the van der Waals gap according to both approaches, which also yield consistent predictions concerning the interlayer metallic bonding in BiTeI under compression. It is consequently shown that the calculated band-gap energies follow qualitatively and quantitatively the same trend within the two approximations employed here, and the transition to the zero-gap state occurs at the same critical width of the van der Waals gap.

This is more good evidence that we have a pretty good handle on these things by now.

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Tidal Disruption of Dark Matter Solves Missing Satellite Problem

by Tommy on 18/10/2016

This has also been out for a while. It’s still worth reading I guess. And it’s free!;

Tidal stirring of satellites with shallow density profiles prevents them from being too big to fail, Mihai Tomozeiu, Lucio Mayer and Thomas Quinn, The Astrophysical Journal Letters, 827, 1 (5 August 2016), doi:10.3847/2041-8205/827/1/L15

The “too big to fail” problem is revisited by studying the tidal evolution of populations of dwarf satellites with different density profiles. The high-resolution cosmological ΛCDM “ErisMod” set of simulations is used. These simulations can model both the stellar and dark matter components of the satellites, and their evolution under the action of the tides of a Milky Way (MW)-sized host halo at a force resolution better than 10 pc. The stronger tidal mass loss and re-shaping of the mass distribution induced in satellites with γ = 0.6 dark matter density distributions, as those resulting from the effect of feedback in hydrodynamical simulations of dwarf galaxy formation, are sufficient to bring the circular velocity profiles in agreement with the kinematics of MW’s dSphs. In contrast, in simulations in which the satellites retain cusps at z = 0 there are several “massive failures” with circular velocities in excess of the observational constraints. Various sources of deviations in the conventionally adopted relation between the circular velocity at the half-light radius and the one-dimensional line of sight velocity dispersions are found. Such deviations are caused by the response of circular velocity profiles to tidal effects, which also varies depending on the initially assumed inner density profile and by the complexity of the stellar kinematics, which include residual rotation and anisotropy. In addition, tidal effects naturally induce large deviations in the stellar mass–halo mass relation for halo masses below 109 M, preventing any reliable application of the abundance matching technique to dwarf galaxy satellites.

American Astronomical Society Press Release

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A Virtual Zoo of Quantum Topological States of Exotic Matter

by Tommy on 18/10/2016

From the inventor of the subject.

Zoo of quantum-topological phases of matter, Xiao-Gang Wen (13 October 2016)

What are topological phases of matter? First, they are phases of matter at zero temperature. Second, they have a non-zero energy gap. Third, they are more complicated and subtle than the familiar gapped zero temperature phases, such as insulating and magnetic phases. This paper will give a simple introduction and a brief survey of topological phases of matter. We will first discuss topological phases that have topological order. Then we will cover topological phases that have no topological order.

Breakthrough prizes all around. Maybe he’s already got one. I haven’t bothered to look.

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Static Charge Density Waves Stripe Order Found in 1/8 LBCO

by Tommy on 18/10/2016

In other words, CDW order is either cooperative, or competitive, or both. I get that.

This has been out for a while, but now that it has a bona fide press release, it’s official!

Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4, X. M. Chen, V. Thampy, C. Mazzoli, A. M. Barbour, H. Miao, G. D. Gu, Y. Cao, J. M. Tranquada, M. P. M. Dean, and S. B. Wilkins, Phys. Rev. Lett. 117, 167001 (11 October 2016), doi:10.1103/PhysRevLett.117.167001

The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.875Ba0.125CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2¾  h. We discuss the implications of these results for some of the competing theories.

DOE/Brookhaven National Laboratory Press Release

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Ultra Cold Atoms Proposed as a Quantum Critical Simulator

by Tommy on 14/10/2016

Recall that Michael Kosterlitz, David Thouless and Duncan Haldane were recently awarded their Nobel Prizes in condensed matter physics. Recall also that I have recently proposed a bosonic superfluid dark matter and dark energy hypothesis, where the fundamental excitations of this bosonic quantum superfluid by high energy processes in ordinary and neutron stars, near black holes and other high density high energy exotic states of matter, connect the standard model to Einstein’s equation of gravitation and general relativity through ultra light super axions of some sort, in my rather lame and naive attempt to jump start a new quantum gravity and quantum cosmology unification. I have previously proposed that condensed matter and ultra cold atom trapping theories, experiments and numerical simulations are the ONLY way that we will be able to access this energy regime, and that already this has revolutionized our understanding of fundamental physics and its application to novel device physics. In fact, I have also already employed this strategy successfully on the origin of life problem. Therefore, I present here …

Quantitative Studies on the Quantum Critical Regime near Superfluid to Mott Insulator Transition, Hao Lee, Shiang Fang and Daw-Wei Wang (12 October 2016)

We investigate the critical behaviors of correlation length and critical exponents for strongly interacting bosons in a two-dimensional optical lattice via quantum Monte Carlo simulations. By comparing the full numerical results to those given by the effective theory, we quantitatively determine the critical regime where the universal scaling behaviors applies for both classical Berezinskii-Kosterlitz-Thouless transition at a finite temperature and quantum phase transition from superfluid to Mott insulator. Our results show that the critical regime can be as large as a few lattice sites in optical lattice and should be observable in present experimental conditions.

Quantum critical black hole collapse in on the horizon.

So is room temperature superconductivity.

I predict weirdness very soon now.

I could be wrong though.

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Gravitational Anomalies, Entanglement Entropy, Anomaly Inflow

by Tommy on 14/10/2016

This is another result from the University of Illinois – Urbana Champaign school of thought, that I have found to be extremely useful for my dark matter gravitational super duper axion hypothesis.

Entanglement Entropy & Anomaly Inflow, Taylor L. Hughes, Robert G. Leigh, Onkar Parrikar and Srinidhi T. Ramamurthy, Phys. Rev. D, 93, 065059 (30 March 2016)

We study entanglement entropy for parity-violating (time-reversal breaking) quantum field theories on R1,2 in the presence of a domain wall between two distinct parity-odd phases. The domain wall hosts a 1+1-dimensional conformal field theory (CFT) with non-trivial chiral central charge. Such a CFT possesses gravitational anomalies. It has been shown recently that, as a consequence, its intrinsic entanglement entropy is sensitive to Lorentz boosts around the entangling surface. Here, we show using various methods that the entanglement entropy of the three-dimensional bulk theory is also sensitive to such boosts owing to parity-violating effects, and that the bulk response to a Lorentz boost precisely cancels the contribution coming from the domain wall CFT. We argue that this can naturally be interpreted as entanglement inflow (i.e., inflow of entanglement entropy analogous to the familiar Callan-Harvey effect) between the bulk and the domain-wall, mediated by the low-lying states in the entanglement spectrum. These results can be generally applied to 2+1-d topological phases of matter that have edge theories with gravitational anomalies, and provide a precise connection between the gravitational anomaly of the physical edge theory and the low-lying spectrum of the entanglement Hamiltonian.

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Paleocene Eocene Thermal Maximum (PETM) Assigned to a Comet Impact

by Tommy on 14/10/2016

Impact ejecta at the Paleocene-Eocene boundary, Morgan F. Schaller, Megan K. Fung, James D. Wright, Miriam E. Katz and Dennis V. Kent, Science, 354, 6309, 225-229 (14 October 2016), DOI:10.1126/science.aaf5466

Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.

My interests in these kinds of subjects started slowly and developed over a long period of time. Originally it started back in 1989, on the day of the Loma Prieta earthquake that occurred on October 17th, 1989. I was actually working in a foramanifera laboratory at the Caribbean Marine Research Center CMRC at Lee Stocking Island in the Exuma Cays in the Bahamas at that time.

I wasn’t doing that kind of research, but I was interested in it since it was occurring all around me, and I suddenly found myself surrounded by geologists and biologists, subjects which I knew little or nothing about. And we had a tide gauge. And I had an island. So by then I was totally keyed into the tides.

So on that day I was desperately trying to get back to the states, trying to negotiate a ride on Mr. and Mrs. Perry’s private plane, with them, the owners of the island on which the research center was located, who did not particularly like me and viewed everything I did with suspicion. That’s another story entirely. I was bumped off the flight the previous week, and their private flight was my only option. So I went home to cool my jets, and on my way back down to the cay to catch that ride, as I was walking down the hill to the dock, I ran into the highest tide I have ever EVER witnessed in all the years I had spent in the Bahamas. It was truly an awesome tide, it covered up jagged coral rocks that had never been covered before, rocks that can rip the bottom out of your boat if you don’t see them. It was a totally off the scale high tide. It was the only subject of discussion when I arrived at the lab, and that tide alone prompted a complete rebuild of the tide gauge column, and eventually a shift to digital tide gauges. Eventually later that day I did get my ride back to West Palm Beach, with Mr. and Mrs. Perry, a very quiet and silent ride indeed, and as I finally arrived in Tampa on my connection, in the airport lobby I was presented with a major earthquake on all of the television screens. Ding! Tides cause earthquakes. I was hooked.

So once the internet arrived on the scene I was ready. It was something that I was watching constantly. So over Christmas vacation 2004 when I was watching the USGS earthquake map and when there I saw an 8.1 major earthquake in the deep southern ocean near the Macquarie Islands, I noticed. I thought to myself that something is on the move down there, and if there is one, there should be another, and so for the next few days I was watching that map like a hawk, and when it happened, I saw it. I was on it. The Boxing Day Indonesian earthquake and tsunami.

Massive Quake Strikes Remote Macquarie Island In Antarctica

I was posting on sci.earthquake at the time, and I wish now I had said something earlier, not just after the fact. I felt that way when I was sitting in Grandma’s chair watching the Columbia space shuttle launch on its final mission, when I saw something fall off the rocket and shred into the exhaust plumes of the solid rocket boosters. I was so concerned about it that I ran out into the back yard thinking I would catch the explosion, but there it was, cleanly accelerating over the horizon and into space. So I thought all is well, when in fact all was not well, and I regret to this day not relaying my observations and thoughts to the space cadet community on the usenet.

Between those two incidents and all of my experiences in search and rescue in the Bahamas – I decided right then and there, on Boxing Day in 2004, if I see something then I am reporting it.

At that point I was seeing a lot of things I did not like. It was in the middle of the Bush years. So when I noticed that Ellen Thomas was coming to Eckerd College in St. Petersburg to speak on global warming and the PETM on February 16th, 2005, I went down there to see her, and after the talk, I spoke with her. At that time comet impacts were considered fringe, but she gave me some pointers and again, I was hooked. Ellen Prager was my boss for a year in 1995 and so I was already a catastrophist. And of course, catastrophe was a daily occurrence at the research lab and in the islands. Crisis management and science and problem solving was my way of life.

So when the Younger Dryas impact hypothesis arrived on the scene, of course I was interested, and when on Darwin’s Day in 2009, when I saw something in the Black Sturgeon River Basin south of Lake Nipigon in Ontario, Canada, of course, I reported it. On Valentines Day. February 14, 2009. So even when I am wrong, and I am mostly wrong nowadays, I don’t regret reporting what I see. That’s my story and I’m sticking with it. Until I see that I am wrong. I am a scientist.

This is my microphone.

Update: The takeaway is that big impacts can cause earthquakes, tsunamis and volcanoes.

Supervolcanoes and volcanism is well known to release large amounts of carbon dioxide.

Positive feedbacks in these phenomena could well include large methane releases.

Instantaneous effects of an impact are followed by long term effects.

Therefore I consider this problem now to be solved.

Update 2: Wow, I just realized this is a five way super catastrophe.

Cosmic impact, massive earthquake swarm, giant tsunami, super volcanism and then when the coal beds burned up in that mess, global warming. Life is great, no? I’m a catastrophist!

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Trillions and Trillions

by Tommy on 14/10/2016
Hubble Trillions Of Galaxies

Hubble Trillions Of Galaxies

The Evolution of Galaxy Number Density at z < 8 and its Implications, Christopher J. Conselice, Aaron Wilkinson, Kenneth Duncan and Alice Mortlock, Accepted to ApJ (9 October 2016)

The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z ∼ 8 to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies (ϕT), more massive than M = 106 M, decreases as ϕTt−1, where t is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M > 107 M. By using the M = 106 M lower limit we further show that the total number of galaxies in the universe up to z = 8 is 2.0+0.7−0.6 × 1012 (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox.

Darkness seems to be winning in my universe.

And so I say – let there be light.

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Bismuth Topological Edge States Proposed for Thermoelectric ZT Efficiency Enhancements

by Tommy on 13/10/2016

Effects of topological edge states on the thermoelectric properties of Bi nanoribbons, L. Cheng, H. J. Liu, J. H. Liang, J. Zhang, J. Wei, P. H. Jiang and D. D. Fan (11 October 2016)

Using first-principles calculations combined with Boltzmann transport theory, we investigate the effects of topological edge states on the thermoelectric properties of Bi nanoribbons. It is found that there is a competition between the edge and bulk contributions to the Seebeck coefficients. However, the electronic transport of the system is dominated by the edge states because of its much larger electrical conductivity. As a consequence, a room temperature value exceeding 3.0 could be achieved for both p- and n-type systems when the relaxation time ratio between the edge and the bulk states is tuned to be 1000. Our theoretical study suggests that the utilization of topological edge states might be a promising approach to cross the threshold of the industrial application of thermoelectricity.

Eggimuffin. Yeah. Maybe.

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Time and Angle Resolved Photoemission Spectroscopy Probes Effects of Dirac Cone Warping on Transport and Structure of a Topological Superconductor – Bismuth Telluride – Bi2Te3

by Tommy on 12/10/2016

Observation of antiphase coherent phonons in the warped Dirac cone of Bi2Te3, E. Golias and J. Sánchez-Barriga, Phys. Rev. B 94, 161113R (11 October 2016), doi:PhysRevB.94.161113

In this Rapid Communication we investigate the coupling between excited electrons and phonons in the highly anisotropic electronic structure of the prototypical topological insulator Bi2Te3. Using time- and angle-resolved photoemission spectroscopy we are able to identify the emergence and ultrafast temporal evolution of the longitudinal-optical A1g coherent-phonon mode in Bi2Te3. We observe an antiphase behavior in the onset of the coherent-phonon oscillations between the ΓK¯ and the ΓM¯ high-symmetry directions that is consistent with warping. The qualitative agreement between our density-functional theory calculations and the experimental results reveals the critical role of the anisotropic coupling between Dirac fermions and phonon modes in the topological insulator Bi2Te3.

See also: Lightsources Article

Hot off the press.

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Bismuth Bi (111) and (110) Through Ultra Thin Nanowires

by Tommy on 12/10/2016

Electronic and structural properties of rhombohedral [111] and [110] oriented ultra-thin bismuth nanowires, Lida Ansari, Farzan Gity and James C. Greer (19 September 2016)

Structures and electronic properties of rhombohedral [111] and [110] bismuth nanowires are calculated with the use of density functional theory. The formation of an energy band gap from quantum confinement is studied and to improve estimates for the band gap the GW approximation is applied. The [111] oriented nanowires require surface bonds to be chemically saturated to avoid formation of metallic surface states whereas the surface of the [110] nanowires do not support metallic surface states. It is found that the onset of quantum confinement in the surface passivated [111] nanowires occurs at larger critical dimensions than for the [110] nanowires. For the [111] oriented nanowires it is predicted that a band gap of approximately 0.5 eV can be formed at a diameter of approximately 6 nm, whereas for the [110] oriented nanowires a diameter of approximately 3 nm is required to achieve a similar band gap energy. The GW correction is also applied to estimates of the electron affinity, ionisation potentials and work functions for both orientations of the nanowires for various diameters below 5 nm. The magnitude of the energy band gaps that arise in bismuth at critical dimensions of a few nanometers are of the same order as for conventional bulk semiconductors.

This is fairly brute force but the trends here are clearly distinguishable.

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Quantum Confinement Effect in Bismuth Multilayers Proposed for Conventional Electronics

by Tommy on 12/10/2016

Reinventing Solid State Electronics: Harnessing Quantum Confinement in Bismuth Thin Films, Farzan Gity, Lida Ansari, Martin Lanius, Peter Schüffelgen, Gregor Mussler, Detlev Grützmacher and James C. Greer (17 September 2016)

Solid state electronics relies on the intentional introduction of impurity atoms or dopants into a semiconductor crystal and/or the formation of junctions between different materials (heterojunctions) to create rectifiers, potential barriers, and conducting pathways. With these building blocks, switching and amplification of electrical currents and voltages is achieved. As miniaturization continues to ultra-scaled transistors with critical dimensions on the order of ten atomic lengths, the concept of doping to form rectifying junctions fails and heterojunction formation becomes extremely difficult. Here it is shown there is no need to introduce dopant atoms nor is the formation of a heterojunction required to achieve the fundamental electronic function of current rectification. Ideal diode behavior or rectification is achieved for the first time solely by manipulation of quantum confinement in approximately 2 nanometer thick films consisting of a single atomic element, the semimetal bismuth. Crucially for nanoelectronics, this new quantum approach enables room temperature operation.

I’m not exactly sure if diode electronics is the way to go with these things.

I have this terrible pain down my left side.

I’m feeling very depressed.

I might be paranoid.

I need positrons.

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New Detection Technique for Ultralight Dark Matter Axions

by Tommy on 11/10/2016

This is getting some press.

Broadband and Resonant Approaches to Axion Dark Matter Detection, Yonatan Kahn, Benjamin R. Safdi and Jesse Thaler, Phys. Rev. Lett. 117, 141801 (30 September 2016)

When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axionlike dark matter with masses in the range of 10−14 − 10−6 eV. In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant.

This closes the gap with ADMX.

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Berry Curvature Induction in Lattice QCD Simulations Revealed

by Tommy on 11/10/2016

This has been extremely helpful to my dark matter axion program.

Lattice QCD simulation of the Berry curvature, Arata Yamamoto, Talk Given at 34th Annual International Symposium on Lattice Field Theory – Lattice 2016 (7 October 2016)

The Berry curvature is a fundamental concept describing topological order of quantum systems. While it can be analytically tractable in non-interacting systems, numerical simulations are necessary in interacting systems. We present a formulation to calculate the Berry curvature in lattice QCD.

See also:

Berry phase in lattice QCD, Arata Yamamoto, Phys. Rev. Lett. 117, 052001 (2016), DOI:10.1103/PhysRevLett.117.052001

We propose the lattice QCD calculation of the Berry phase which is defined by the ground state of a single fermion. We perform the ground-state projection of a single-fermion propagator, construct the Berry link variable on a momentum-space lattice, and calculate the Berry phase. As the first application, the first Chern number of the (2+1)-dimensional Wilson fermion is calculated by the Monte Carlo simulation.

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Current Induced Giant Diamagnetism in the Mott Insulator Calcium Ruthenate Ca2RuO4

by Tommy on 11/10/2016

When I see something this novel and interesting all I can do is repeat it verbatim.

Current Induced Giant Diamagnetism in the Mott Insulator Ca2RuO4, Chanchal Sow, Shingo Yonezawa, Sota Kitamura, Takashi Oka, Kazuhiko Kuroki, Fumihiko Nakamura and Yoshiteru Maeno (7 October 2016)

Mott insulators have surprised us many times by hosting new and diverse quantum phenomena when the frozen electrons are perturbed by various stimuli. Superconductivity, metal-insulator transition, and colossal magnetoresistance induced by element substitution, pressure, and magnetic field are prominent examples. Here we report a novel phenomenon, namely giant diamagnetism, in the Mott insulator Ca2RuO4 induced by electric current. With application of 1 A/cm2 current, the strongest diamagnetism among all nonsuperconducting materials is induced as the system is tuned to a semimetallic state. The origin lies in the emergence of indirect Dirac cones in the many-body spectrum and associated monopole-like anomaly in the momentum dependent susceptibility. This record-breaking and switchable diamagnetism is a new class of non-equilibrium quantum phenomena on the verge of Mott insulating states.

See also:

Current Induced Giant Diamagnetism in the Mott Insulator Ca2RuO4, D. Sutter, C.G. Fatuzzo, S. Moser, M. Kim, R. Fittipaldi, A. Vecchione, V. Granata, Y. Sassa, F. Cossalter, G. Gatti, M. Grioni, H.M. Ronnow, N.C. Plumb, C.E. Matt, M. Shi, M. Hoesch, T.K. Kim, T.R. Chang, H.T. Jeng, C. Jozwiak, A. Bostwick, E. Rotenberg, A. Georges, T. Neupert and J. Chang (10 October 2016)

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund’s coupling is realised in Ca2RuO4. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide — using angle-resolved photoemission electron spectroscopy – the band structure of the paramagnetic insulating phase of Ca2RuO4 and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund’s coupling J = 0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the dxy orbital due to c-axis contraction is shown to be important in explaining the nature of the insulating state. It is thus a combination of multiband physics, Coulomb interaction and Hund’s coupling that generates the Mott insulating state of Ca2RuO4. These results underscore the importance of Hund’s coupling in the ruthenates and related multiband materials.

I like where this is going.

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Electron Mass Enhanced Quantum Critical Material Proposed for Helium Free Cryogenic Refrigeration

by Tommy on 11/10/2016

Super-heavy electron material as metallic refrigerant for adiabatic demagnetization cooling, Yoshifumi Tokiwa, Boy Piening, Hirale S. Jeevan, Sergey L. Bud’ko, Paul C. Canfield and Philipp Gegenwart, Science Advances, 2, 9, e1600835 (9 September 2016), DOI:10.1126/sciadv.1600835

Low-temperature refrigeration is of crucial importance in fundamental research of condensed matter physics, because the investigations of fascinating quantum phenomena, such as superconductivity, superfluidity, and quantum criticality, often require refrigeration down to very low temperatures. Currently, cryogenic refrigerators with 3He gas are widely used for cooling below 1 K. However, usage of the gas has been increasingly difficult because of the current worldwide shortage. Therefore, it is important to consider alternative methods of refrigeration. We show that a new type of refrigerant, the super-heavy electron metal YbCo2Zn20, can be used for adiabatic demagnetization refrigeration, which does not require 3He gas. This method has a number of advantages, including much better metallic thermal conductivity compared to the conventional insulating refrigerants. We also demonstrate that the cooling performance is optimized in Yb1−xScxCo2Zn20 by partial Sc substitution, with x ~ 0.19. The substitution induces chemical pressure that drives the materials to a zero-field quantum critical point. This leads to an additional enhancement of the magnetocaloric effect in low fields and low temperatures, enabling final temperatures well below 100 mK. This performance has, up to now, been restricted to insulators. For nearly a century, the same principle of using local magnetic moments has been applied for adiabatic demagnetization cooling. This study opens new possibilities of using itinerant magnetic moments for cryogen-free refrigeration.

This is yet another step in the right direction.

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Bismuth Oxy Iodide (BiOI) Proposed as Efficient Excitonic Water Electrolysis Photocatalyst

by Tommy on 11/10/2016

Spatial separation of photo-generated electron-hole pairs in BiOBr/BiOI bilayer to facilitate water splittingSpatial separation of photo-generated electron-hole pairs in BiOBr/BiOI bilayer to facilitate water splitting, Zhen-Kun Tang, Wen-Jin Yin, Le Zhang, Bo Wen, Deng-Yu Zhang, Li-Min Liu and Woon-Ming Lau, Scientific Reports 6, 32764 (2 September 2016), doi:10.1038/srep32764

The electronic structures and photocatalytic properties of bismuth oxyhalide bilayers (BiOX1/BiOX2, X1 and X2 are Cl, Br, I) are studied by density functional theory. Briefly, their compositionally tunable bandgaps range from 1.85 to 3.41 eV, suitable for sun-light absorption, and all bilayers have band-alignments good for photocatalytic water-splitting. Among them, heterogeneous BiOBr/BiOI bilayer is the best as it has the smallest bandgap. More importantly, photo-excitation of BiOBr/BiOI leads to electron supply to the conduction band minimum with localized states belonging mainly to bismuth of BiOBr where the H+/H2 half-reaction of water-splitting can be sustained. Meanwhile, holes generated by such photo-excitation are mainly derived from the iodine states of BiOI in the valence band maximum; thus, the O2/H2O half-reaction of water splitting is facilitated on BiOI. Detailed band-structure analysis also indicates that this intriguing spatial separation of photo-generated electron-hole pairs and the two half-reactions of water splitting are good for a wide photo-excitation spectrum from 2–5 eV; as such, BiOBr/BiOI bilayer can be an efficient photocatalyst for water-splitting, particularly with further optimization of its optical absorptivity.

I have heard something like this before somewhere.

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Spin Orbit Coupling (SOC) Applied to the BCS-BEC Transition

by Tommy on 3/10/2016

BCS-BEC transition in a Dilute Bose Gas with Spin-Orbit Coupling, Dekun Luo, Rong Li and Lan Yin (30 September 2016)

We study a two-component Bose gas with a symmetric spin-orbit coupling, and find that two atoms can form a bound state with any intra- or inter-species scattering length. Consequently, in the dilute limit, a stable condensation of diatomic molecules in the Bardeen-Cooper-Shrieffer (BCS) pairing state can be formed with weakly-attractive inter-species and repulsive intra-species interactions. This BCS paring state is energetically favored over Bose-Einstein condensation (BEC) of atoms at low densities, but as the density increases, there is a first-order transition from the BCS to BEC states.

Cool. When can we start?

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I’m Your Captain – Return Me My Ship

by Tommy on 1/10/2016

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Two Dimensional (2D) Time Reversal Symmetry (TRS) Breaking Topological Superconductivity Found in Bismuth Nickel Bilayers

by Tommy on 30/09/2016

This was the last thing I reported on here at the Blob almost a year ago, before I ran off the rails on my axion dark matter adventure. Now this subject has escalated into something that is very interesting, although possibly not p-wave topological superconductivity as was first suggested.

Time-Reversal-Symmetry-Breaking Superconductivity in Epitaxial Bismuth/Nickel Bilayers, Xinxin Gong, Mehdi Kargarian, Alex Stern, Di Yue, Hexin Zhou, Xiaofeng Jin, Victor M. Galitski, Victor M. Yakovenko and Jing Xia (27 September 2016)

Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of 3D crystals with bulk inversion symmetry. Here we report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet. We propose a theoretical model where magnetic fluctuations in Ni induce superconducting pairing of the dxy ± idx2 – y2 orbital symmetry between the electrons in Bi. This order parameter spontaneously breaks the TRS and has a non-zero phase winding number around the Fermi surface, thus making Bi/Ni a rare example of a 2D topological superconductor.

Supplementary Information:

See also:

Time reversal symmetry breaking superconductivity in topological materials, Yunsheng Qiu, Kyle Nocona Sanders, Jixia Dai, Julia E. Medvedeva, Weida Wu, Pouyan Ghaemi, Thomas Vojta and Yew San Hor (11 Decenber 2015)

Fascinating phenomena have been known to arise from the Dirac theory of relativistic quantum mechanics, which describes high energy particles having linear dispersion relations. Electrons in solids usually have non-relativistic dispersion relations but their quantum excitations can mimic relativistic effects. In topological insulators, electrons have both a linear dispersion relation, the Dirac behavior, on the surface and a non-relativistic energy dispersion in the bulk. Topological phases of matter have attracted much interest, particularly broken-symmetry phases in topological insulator materials. Here, we report by Nb doping that the topological insulator Bi2Se3 can be turned into a bulk type-II superconductor while the Dirac surface dispersion in the normal state is preserved. A macroscopic magnetic ordering appears below the superconducting critical temperature of 3.2 K indicating a spontaneous spin rotation symmetry breaking of the Nb magnetic moments. Even though such a magnetic order may appear at the edge of the superconductor, it is mediated by superconductivity and presents a novel phase of matter which gives rise to a zero-field Hall effect.

Next up, ARPES examination of this system.

This is gonna be big. Super big.

The adventure continues.

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Happy National Coffee Day – September 29, 2016

by Tommy on 29/09/2016
National Coffee Day

National Coffee Day

Say, pardon me but, could you help out a fellow American who’s down on his luck?

Humphrey Bogart Bugs Bunny

Humphrey Bogart Bugs Bunny

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Modified Gravity by Cosmic QCD Super Axion Boson Excitation

by Tommy on 27/09/2016

Here I clearly and officially state my gravitational cosmic QCD axion scaling hypothesis.

With this I bring fa down to a reasonable TeV Higgs scale level, depending upon density, etc. and solve numerous other cosmological conundrums, using geometry, topology and superfluidity in condensed matter physics systems as my guide. I’ve already solved the origin of life problem.

The Radial Acceleration Relation in Rotationally Supported Galaxies, Stacy McGaugh, Federico Lelli and Jim Schombert, Accepted for Publication in Physical Review Letters (19 September 2016)

We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.

No MACHOs or WIMPs and SUSY etc. lost into the black hole.

Mimicking dark matter in Horndeski gravity, Massimiliano Rinaldi (12 August 2016)

Since the rediscovery of Horndeski gravity, a lot of work has been devoted to the exploration of its properties, especially in the context of dark energy. However, one sector of this theory, namely the one containing the coupling of the Einstein tensor to the kinetic term of the scalar field, shows some surprising features in the construction of black holes and neutron stars. Motivated by these new results, I explore the possibility that this sector of Horndeski gravity can mimic cold dark matter at cosmological level and also explain the flattening of galactic rotation curves. I will show that it is possible to achieve both goals with a minimal set of assumptions.

If it mimics or simulates dark matter, then it IS dark matter.


Gauge Fields, Nonlinear Realizations, Supersymmetry, E.A. Ivanov, Physics of Particles and Nuclei (4 September 2016), DOI:10.1134/S1063779616040080

This is a brief survey of the all-years research activity in the Sector “Supersymmetry” (the former Markov Group) at the Bogoliubov Laboratory of Theoretical Physics. The focus is on the issues related to gauge fields, spontaneously broken symmetries in the nonlinear realizations approach, and diverse aspects of supersymmetry.

Ask an expert!

So if it’s not supersymmetry, then what is it?

The Inverse Higgs Phenomenon in Nonlinear Realizations, E. A. Ivanov and V. I. Ogievetsky, Teor. Mat. Fiz., 25, 164-177, Translated from Teoreticheskaya i Matematicheskaya Fizika

(27 February 1975), DOI:10.1007/BF01028947

Ok, so I’m gonna need a new axion. A super axion!

Coupled to gravitons and ordinary matter through the Higgs.

This is my special theory of gravity modification.

My working hypothesis of dark matter.

© 2016 Thomas Lee Elifritz

Now I just need a theory.

ITS gonna be weird.

Trust me on that.

Update: Alternatively you could push fa up to Planck scale, since it’s already a good fraction of the way there. What this does is make the mass of the axion more uncertain. But since I’m taking my clues from lattice QCD in a gravitationally flat environment, it probably doesn’t matter.

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The Beginning

by Tommy on 27/09/2016

The end is really just the beginning.

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The End

by Tommy on 25/08/2016

So it’s been almost but not quite two full years since I started this latest incarnation of the Blob.

Besides continually reminding myself that I’m a crackpot, I’ve come to the realization that I have no reason to continue doing this. My viewership is extremely limited, the subject matter here is arcane and bizarre, and I’ve solved most of the problems I set out to solve within my truncated intellectual and financial capabilities. The door has been opened, and it can’t be shut anymore.

So absent any external funding, it’s goodbye.

See ya on the other side.

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Novel Topological Insulator β-Bi4I4 Now Studied in Great Detail

by Tommy on 25/08/2016


I had blogged it earlier when it was still just an APS meeting abstract, now here it is.

A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4, A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4, Gabriel Autès, Anna Isaeva, Luca Moreschini, Jens C. Johannsen, Andrea Pisoni, Ryo Mori, Wentao Zhang, Taisia G. Filatova, Alexey N. Kuznetsov, László Forró, Wouter Van den Broek, Yeongkwan Kim, Keun Su Kim, Alessandra Lanzara, Jonathan D. Denlinger, Eli Rotenberg, Aaron Bostwick, Marco Grioni and Oleg V. Yazyev, Nature Materials, 15, 154–158 (14 December 2015), doi:10.1038/nmat4488

Recent progress in the field of topological states of matter has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators, followed by closely related ternary compounds and predictions of several weak TIs. However, both the conceptual richness of Z2 classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z2 topological insulator is theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide β-Bi4I4. The electronic structure of β-Bi4I4, characterized by Z2 invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements performed on the (001) surface reveal a highly anisotropic band-crossing feature located at the M point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.

See also:

Topological insulators: Quasi-1D topological insulators, Huaqing Huang and Wenhui Duan, Nature Materials, 15, 129–130 (22 January 2016), doi:10.1038/nmat4543

Bismuth iodide Bi4I4, composed of quasi-one-dimensional molecular chains, was theoretically predicted and now has been experimentally verified to be a novel strong topological insulator.

So it’s nice to see this subject taken to completion.

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Michael F. Siemion, Instructor, Wisconsin School of Electronics

by Tommy on 24/08/2016
Michael F. Siemion - Instructor - Wisconsin School of Electronics

Michael F. Siemion – Instructor – Wisconsin School of Electronics

I wasn’t old enough to get into the school. He tutored me privately.

Electronics and semiconductor physics – at a very early age.

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Condensed Matter Physics – Practical Cosmological Results

by Tommy on 24/08/2016

Surprises with Nonrelativistic Naturalness, Petr Horava, Int. J. Mod. Phys. D25, 1645007 (22 August 2016)

We explore the landscape of technical naturalness for nonrelativistic systems, finding surprises which challenge and enrich our relativistic intuition already in the simplest case of a single scalar field. While the immediate applications are expected in condensed matter and perhaps in cosmology, the study is motivated by the leading puzzles of fundamental physics involving gravity: The cosmological constant problem and the Higgs mass hierarchy problem.

Of course, nowadays, not all condensed matter physics is nonrelativistic.

That will be the game changer here.

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Cuprate Charge Density Modulations and Real Space Physics

by Tommy on 23/08/2016

Commensurate 4a0 period Charge Density Modulations throughout the Bi2Sr2CaCu2O8+x Pseudogap Regime, A. Mesaros, K. Fujita, S. D. Edkins, M. H. Hamidian, H. Eisaki, S. Uchida, J. C. Séamus Davis, M. J. Lawler and Eun-Ah Kim (22 August 2016)

Theories based upon strong real space (r-space) electron electron interactions have long predicted that unidirectional charge density modulations (CDM) with four unit cell (4a0) periodicity should occur in the hole doped cuprate Mott insulator (MI). Experimentally, however, increasing the hole density p is reported to cause the conventionally defined wavevector QA of the CDM to evolve continuously as if driven primarily by momentum space (k-space) effects. Here we introduce phase resolved electronic structure visualization for determination of the cuprate CDM wavevector. Remarkably, this new technique reveals a virtually doping independent locking of the local CDM wavevector at |Q0|=2π/4a0 throughout the underdoped phase diagram of the canonical cuprate Bi2Sr2CaCu2O8. These observations have significant fundamental consequences because they are orthogonal to a k-space (Fermi surface) based picture of the cuprate CDM but are consistent with strong coupling r-space based theories. Our findings imply that it is the latter that provide the intrinsic organizational principle for the cuprate CDM state.

Well it looks like we’ve come full circle again.

This is a carnival ride from hell.

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Lattice QCD Calculations Applied To Axion Cosmology

by Tommy on 22/08/2016

Lattice QCD for Cosmology, Sz. Borsanyi, Z. Fodor, K. H. Kampert, S. D. Katz, T. Kawanai, T. G. Kovacs, S. W. Mages, A. Pasztor, F. Pittler, J. Redondo, A. Ringwald and K. K. Szabo (27 Jun 2016)

We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion’s mass in the post-inflation scenario and/or give the relationship between the axion’s mass and the universal axionic angle, which acts as a initial condition of our universe.

Finally this is getting the treatment it deserves from the experts.

Fractions of an meV puts it at liquid helium temperatures.

Or alternatively, in the realm of the CMB.

See also:

Unifying inflation with the axion, dark matter, baryogenesis and the seesaw mechanism, Guillermo Ballesteros, Javier Redondo, Andreas Ringwald and Carlos Tamarit (18 August 2016)

A minimal extension of the Standard Model (SM) providing a complete and consistent picture of particle physics and cosmology up to the Planck scale is presented. We add to the SM three right-handed SM-singlet neutrinos, a new vector-like color triplet fermion and a complex SM singlet scalar σ whose vacuum expectation value at ∼1011 GeV breaks lepton number and a Peccei-Quinn symmetry simultaneously. Primordial inflaton is produced by a combination of σ and the SM Higgs. Baryogenesis proceeds via thermal leptogenesis. At low energies, the model reduces to the SM, augmented by seesaw-generated neutrino masses, plus the axion, which solves the strong CP problem and accounts for the dark matter in the Universe. The model can be probed decisively by the next generation of cosmic microwave background and axion dark matter experiments.

But but but … gravitation!

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High Tc of Cuprates Attributed to Small Local Electronic Pairs

by Tommy on 22/08/2016

Dependence of the critical temperature in overdoped copper oxides on superfluid density, I. Božović, X. He, J. Wu and A. T. Bollinger, Nature, 536, 309–311 (18 August 2016), doi:10.1038/nature19061

The physics of underdoped copper oxide superconductors, including the pseudogap, spin and charge ordering and their relation to superconductivity is intensely debated. The overdoped copper oxides are perceived as simpler, with strongly correlated fermion physics evolving smoothly into the conventional Bardeen–Cooper–Schrieffer behaviour. Pioneering studies on a few overdoped samples indicated that the superfluid density was much lower than expected, but this was attributed to pair-breaking, disorder and phase separation. Here we report the way in which the magnetic penetration depth and the phase stiffness depend on temperature and doping by investigating the entire overdoped side of the La2−xSrxCuO4 phase diagram. We measured the absolute values of the magnetic penetration depth and the phase stiffness to an accuracy of one per cent in thousands of samples; the large statistics reveal clear trends and intrinsic properties. The films are homogeneous; variations in the critical superconducting temperature within a film are very small (less than one kelvin). At every level of doping the phase stiffness decreases linearly with temperature. The dependence of the zero-temperature phase stiffness on the critical superconducting temperature is generally linear, but with an offset; however, close to the origin this dependence becomes parabolic. This scaling law is incompatible with the standard Bardeen–Cooper–Schrieffer description.

I haven’t read the paper so I can’t comment other than to say … great.

It took them long enough.

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Composite Particle Theory and Fractional Axion Angles

by Tommy on 21/08/2016

As promised earlier, but never delivered, I finally got around to this.

Composite Particle Theory, Fractional Axion Angles, and Extrinsic Twist Defects in Three-Dimensional Gapped Fermionic Phases, Peng Ye, Taylor L. Hughes, Joseph Maciejko and Eduardo Fradkin (21 March 2016)

We study strongly fluctuating compact U(1) × U(1) gauge fields in a parton construction of gapped fermionic phases in three dimensions (3D). In the presence of a background electromagnetic field, the general framework of composite particle theory is proposed in analogy to Jain’s composite fermion theory of 2D fractional quantum Hall states. The resulting gapped phases are constructed by condensing two linearly independent bosonic composite particles, which consist of partons and U(1) × U(1) magnetic monopoles. Charge fractionalization is shown to result from a Debye-Huckel-like screening cloud formed by the condensed composite particles. Our general framework allows us to explore two symmetry-enrichment properties of 3D Abelian topological phases. First, we explore the time-reversal symmetry enrichment characterized by the axion angle Θ. Fractional topological insulators with Θ≠π and time-reversal symmetry are constructed in a concrete example. Second, we generalize the notion of anyonic symmetry of 2D Abelian topological phases to the notion of charge-loop excitation symmetry (Charles) in 3D Abelian topological phases. We propose that line twist defects can be utilized to realize Charles symmetry transformations. We study the non-Abelian fusion properties of such defects and the topological distinction between defect species. Several future directions are proposed.

See also:

Topological superconducting phases from inversion symmetry breaking order in spin-orbit-coupled systems, Yuxuan Wang, Gil Young Cho, Taylor L. Hughes and Eduardo Fradkin (28 April 2016), doi:10.1103/PhysRevB.93.134512

We analyze the superconducting instabilities in the vicinity of the quantum-critical point of an inversion symmetry breaking order. We first show that the fluctuations of the inversion symmetry breaking order lead to two degenerate superconducting (SC) instabilities, one in the s-wave channel, and the other in a time-reversal invariant odd-parity pairing channel (the simplest case being the same as the of 3He-B phase). Remarkably, we find that unlike many well-known examples, the selection of the pairing symmetry of the condensate is independent of the momentum-space structure of the collective mode that mediates the pairing interaction. We found that this degeneracy is a result of the existence of a conserved fermionic helicity, χ, and the two degenerate channels correspond to even and odd combinations of SC order parameters with χ = ± 1. As a result, the system has an enlarged symmetry U(1) × U(1), with each U(1) × U(1) corresponding to one value of the helicity χ. Because of the enlarged symmetry, this system admits exotic topological defects such as a fractional quantum vortex, which we show has a Majorana zero mode bound at its core. We discuss how the enlarged symmetry can be lifted by small perturbations, such as the Coulomb interaction or Fermi surface splitting in the presence of broken inversion symmetry, and we show that the resulting superconducting state can be topological or trivial depending on parameters. The U(1) × U(1) symmetry is restored at the phase boundary between the topological and trivial SC states, and allows for a transition between topologically distinct SC phases without the vanishing of the order parameter. We present a global phase diagram of the superconducting states and discuss possible experimental implications.

From the University of Illinois at Urbana-Champaign.

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Electronic and Mechanical Properties of Single, Bilayer and Multilayer Bismuthene Studied

by Tommy on 21/08/2016

Single and bilayer bismuthene: Stability at high temperature and mechanical and electronic properties, E. Aktürk, O. Üzengi Aktürk, and S. Ciraci, Phys. Rev. B 94, 014115 (20 July 2016), doi:10.1103/PhysRevB.94.014115

Based on first-principles phonon and finite temperature molecular dynamics calculations including spin-orbit coupling, we showed that free-standing single-layer phases of bismuth, namely buckled honeycomb and asymmetric washboard structures named as bismuthene, are stable at high temperature. We studied the atomic structure, mechanical, and electronic properties of these single-layer bismuthene phases and their bilayers. The spin-orbit coupling is found to be crucial in determining lattice constants, phonon frequencies, band gaps, and cohesion. In particular, phonons of 3D hexagonal crystal, as well as those of single-layer bismuthene phases, are softened with spin orbit coupling. By going from 3D hexagonal crystal to free-standing single-layer structures, 2D hexagonal lattice is compressed and semimetal is transformed to semiconductor as a result of confinement effect. On the contrary, by going from single-layer to bilayer bismuthenes, the lattice is slightly expanded and fundamental band gaps are narrowed. Our results reveals that interlayer coupling in multilayer and 3D Bi crystal is crucial for topologically trivial to nontrivial and semimetal to semiconductor transitions.

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