http://www.pnas.org/content/early/2014/09/17/1409701111

Epitaxial growth of large-gap quantum spin Hall insulator on semiconductor surface, Miao Zhou, Wenmei Ming, Zheng Liu, Zhengfei Wang, Ping Li, and Feng Liu, Proceedings of the National Academies of Sciences of the United States of America, PNAS, 22 September 2014

DOI: 10.1073/pnas.1409701111

Quantum phase of matter is of great scientific and technological interest. The quantum spin Hall (QSH) insulator is a newly discovered two-dimensional material that exhibits topological edge state residing inside bulk energy gap, so that its edge is metallic with quantized conductance and its bulk is insulating. For its potential applications in spintronics and quantum computing, a large energy gap is desirable, e.g., for room-temperature application. So far, large-gap QSH insulators have been predicted only in freestanding films. Here we demonstrate the formation of a large-gap QSH state on a semiconductor substrate through epitaxial growth of heavy metal atoms on halogenated Si surface. Our findings not only reveal a new formation mechanism of large-gap QSH insulator, but may also pave the way for its experimental realization.

Formation of topological quantum phase on a conventional semiconductor surface is of both scientific and technological interest. Here, we demonstrate epitaxial growth of 2D topological insulator, i.e., quantum spin Hall state, on Si(111) surface with a large energy gap, based on first-principles calculations. We show that the Si(111) surface functionalized with one-third monolayer of halogen atoms [Si(111)-3√×3√-X (X = Cl, Br, I)] exhibiting a trigonal superstructure provides an ideal template for epitaxial growth of heavy metals, such as Bi, which self-assemble into a hexagonal lattice with high kinetic and thermodynamic stability. Most remarkably, the Bi overlayer is atomically bonded to but electronically decoupled from the underlying Si substrate, exhibiting isolated quantum spin Hall state with an energy gap as large as ∼0.8 eV. This surprising phenomenon originates from an intriguing substrate-orbital-filtering effect, which critically selects the orbital composition around the Fermi level, leading to different topological phases. In particular, the substrate-orbital-filtering effect converts the otherwise topologically trivial freestanding Bi lattice into a nontrivial phase; and the reverse is true for Au lattice. The underlying physical mechanism is generally applicable, opening a new and exciting avenue for exploration of large-gap topological surface/interface states.

Supplemental Supporting Information (PDF)

See also : http://arxiv.org/abs/1401.3392

Large-gap quantum spin Hall state on a semiconductor surface: The orbital filtering by substrate, Miao Zhou, Wenmei Ming, Zheng Liu, Zhengfei Wang, Yugui Yao, Feng Liu

For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate an approach to create the large gap 2D TI state on a semiconductor surface, based on extensive first principles calculations. We show that when Bi, Pb and Au atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, both the Bi@H-Si(111) and Pb@H-Si(111) surfaces exhibit a 2D TI state with a large gap of {greater than} 0.5 eV while the Au@H-Si(111) surface is a trivial insulator. These interesting results are found to originate from the fact that the H-Si(111) surface acts as an atomic orbital filter to critically select the orbital composition around the Fermi level, resulting in different topological phases. In particular, the substrate orbital filtering effect converts the otherwise topologically trivial freestanding Bi and Pb lattices into a nontrivial phase; while the reverse is true for the Au lattice. The physical mechanism underlying this approach is generally applicable, opening up a new and exciting avenue for future design and fabrication of large-gap topological surface/interface states.

So, after almost exactly 20 years, it begins. Unfortunately, this story seems to have taken on a life of its own, reminiscent of the quantum computer in the Forbin Project. The way it sounds Google will have Colossus running on the barge next week, and we’ll have thinking and talking animatronic toys by Christmas. Such is life in the new university press release era of science.

On the Nature of Bismuth (I) Iodide in the Solid State, T. L. Elifritz, Spec. Sci. Tech., 17, 85, 1994

I doubt anyone remembers the 1995 Laboratory of the Year issue of R&D Magazine. Old news.