123 research outputs found
Lifetimes of Shockley electrons and holes at the Cu(111) surface
A theoretical many-body analysis is presented of the electron-electron
inelastic lifetimes of Shockley electrons and holes at the (111) surface of Cu.
For a description of the decay of Shockley states both below and above the
Fermi level, single-particle wave functions have been obtained by solving the
Schr\"odinger equation with the use of an approximate one-dimensional
pseudopotential fitted to reproduce the correct bulk energy bands and
surface-state dispersion. A comparison with previous calculations and
experiment indicates that inelastic lifetimes are very sensitive to the actual
shape of the surface-state single-particle orbitals beyond the
() point, which controls the coupling between the Shockley
electrons and holes.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
Non-Dirac topological surface states in (SnTe)(BiTe)
A new type of topological spin-helical surface states was discovered in
layered van der Waals bonded (SnTe)(BiTe) compounds
which comprise two covalently bonded band inverted subsystems, SnTe and
BiTe, within a building block. This novel topological states
demonstrate non-Dirac dispersion within the band gap. The dispersion of the
surface state has two linear sections of different slope with shoulder feature
between them. Such a dispersion of the topological surface state enables
effective switch of the velocity of topological carriers by means of applying
an external electric field
Self-energy and lifetime of Shockley and image states on Cu(100) and Cu(111): Beyond the GW approximation of many-body theory
We report many-body calculations of the self-energy and lifetime of Shockley
and image states on the (100) and (111) surfaces of Cu that go beyond the
approximation of many-body theory. The self-energy is computed in the framework
of the GW\Gamma approximation by including short-range exchange-correlation
(XC) effects both in the screened interaction W (beyond the random-phase
approximation) and in the expansion of the self-energy in terms of W (beyond
the GW approximation). Exchange-correlation effects are described within
time-dependent density-functional theory from the knowledge of an adiabatic
nonlocal XC kernel that goes beyond the local-density approximation.Comment: 8 pages, 5 figures, to appear in Phys. Rev.
Graph Theory Data for Topological Quantum Chemistry
Topological phases of noninteracting particles are distinguished by global
properties of their band structure and eigenfunctions in momentum space. On the
other hand, group theory as conventionally applied to solid-state physics
focuses only on properties which are local (at high symmetry points, lines, and
planes) in the Brillouin zone. To bridge this gap, we have previously [B.
Bradlyn et al., Nature 547, 298--305 (2017)] mapped the problem of constructing
global band structures out of local data to a graph construction problem. In
this paper, we provide the explicit data and formulate the necessary algorithms
to produce all topologically distinct graphs. Furthermore, we show how to apply
these algorithms to certain "elementary" band structures highlighted in the
aforementioned reference, and so identified and tabulated all orbital types and
lattices that can give rise to topologically disconnected band structures.
Finally, we show how to use the newly developed BANDREP program on the Bilbao
Crystallographic Server to access the results of our computation.Comment: v1: 29 Pages, 13 Figures. Explains how to access the data presented
in arXiv:1703.02050 v2: Accepted version. References updated, figures
improve
Band Connectivity for Topological Quantum Chemistry: Band Structures As A Graph Theory Problem
The conventional theory of solids is well suited to describing band
structures locally near isolated points in momentum space, but struggles to
capture the full, global picture necessary for understanding topological
phenomena. In part of a recent paper [B. Bradlyn et al., Nature 547, 298
(2017)], we have introduced the way to overcome this difficulty by formulating
the problem of sewing together many disconnected local "k-dot-p" band
structures across the Brillouin zone in terms of graph theory. In the current
manuscript we give the details of our full theoretical construction. We show
that crystal symmetries strongly constrain the allowed connectivities of energy
bands, and we employ graph-theoretic techniques such as graph connectivity to
enumerate all the solutions to these constraints. The tools of graph theory
allow us to identify disconnected groups of bands in these solutions, and so
identify topologically distinct insulating phases.Comment: 19 pages. Companion paper to arXiv:1703.02050 and arXiv:1706.08529
v2: Accepted version, minor typos corrected and references added. Now
19+epsilon page
Building Blocks of Topological Quantum Chemistry: Elementary Band Representations
The link between chemical orbitals described by local degrees of freedom and
band theory, which is defined in momentum space, was proposed by Zak several
decades ago for spinless systems with and without time-reversal in his theory
of "elementary" band representations. In Nature 547, 298-305 (2017), we
introduced the generalization of this theory to the experimentally relevant
situation of spin-orbit coupled systems with time-reversal symmetry and proved
that all bands that do not transform as band representations are topological.
Here, we give the full details of this construction. We prove that elementary
band representations are either connected as bands in the Brillouin zone and
are described by localized Wannier orbitals respecting the symmetries of the
lattice (including time-reversal when applicable), or, if disconnected,
describe topological insulators. We then show how to generate a band
representation from a particular Wyckoff position and determine which Wyckoff
positions generate elementary band representations for all space groups. This
theory applies to spinful and spinless systems, in all dimensions, with and
without time reversal. We introduce a homotopic notion of equivalence and show
that it results in a finer classification of topological phases than approaches
based only on the symmetry of wavefunctions at special points in the Brillouin
zone. Utilizing a mapping of the band connectivity into a graph theory problem,
which we introduced in Nature 547, 298-305 (2017), we show in companion papers
which Wyckoff positions can generate disconnected elementary band
representations, furnishing a natural avenue for a systematic materials search.Comment: 15+9 pages, 4 figures; v2: minor corrections; v3: updated references
(published version
Higher-Order Topological Insulators
Three-dimensional topological (crystalline) insulators are materials with an
insulating bulk, but conducting surface states which are topologically
protected by time-reversal (or spatial) symmetries. Here, we extend the notion
of three-dimensional topological insulators to systems that host no gapless
surface states, but exhibit topologically protected gapless hinge states. Their
topological character is protected by spatio-temporal symmetries, of which we
present two cases: (1) Chiral higher-order topological insulators protected by
the combination of time-reversal and a four-fold rotation symmetry. Their hinge
states are chiral modes and the bulk topology is -classified. (2)
Helical higher-order topological insulators protected by time-reversal and
mirror symmetries. Their hinge states come in Kramers pairs and the bulk
topology is -classified. We provide the topological invariants for
both cases. Furthermore we show that SnTe as well as surface-modified
BiTeI, BiSe, and BiTe are helical higher-order topological insulators and
propose a realistic experimental setup to detect the hinge states.Comment: 8 pages (4 figures) and 16 pages supplemental material (7 figures
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