Predicting the strain-mediated topological phase transition in 3D cubic ThTaN3
3
Citation
44
Reference
10
Related Paper
Citation Trend
Abstract:
The cubic ThTaN 3 compound has long been known as a semiconductor with a band gap of approximately 1 eV, but its electronic properties remain largely unexplored. By using density functional theory, we find that the band gap of ThTaN 3 is very sensitive to the hydrostatic pressure/strain. A Dirac cone can emerge around the Γ point with an ultrahigh Fermi velocity at a compressive strain of 8%. Interestingly, the effect of spin–orbital coupling (SOC) is significant, leading to a band gap reduction of 0.26 eV in the ThTaN 3 compound. Moreover, the strong SOC can turn ThTaN 3 into a topological insulator with a large inverted gap up to 0.25 eV, which can be primarily attributed to the inversion between the d-orbital of the heavy element Ta and the p-orbital of N. Our results highlight a new 3D topological insulator with strain-mediated topological transition for potential applications in future spintronics.Keywords:
Topological insulator
Hydrostatic pressure
Room-temperature realization of macroscopic quantum phenomena is one of the major pursuits in fundamental physics. The quantum spin Hall state, a topological quantum phenomenon that features a two-dimensional insulating bulk and a helical edge state, has not yet been realized at room temperature. Here, we use scanning tunneling microscopy to visualize a quantum spin Hall edge state on the surface of the higher-order topological insulator Bi4Br4. We find that the atomically resolved lattice exhibits a large insulating gap of over 200meV, and an atomically sharp monolayer step edge hosts a striking in-gap gapless state, suggesting the topological bulk-boundary correspondence. An external magnetic field can gap the edge state, consistent with the time-reversal symmetry protection inherent to the underlying topology. We further identify the geometrical hybridization of such edge states, which not only attests to the Z2 topology of the quantum spin Hall state but also visualizes the building blocks of the higher-order topological insulator phase. Remarkably, both the insulating gap and topological edge state are observed to persist up to 300K. Our results point to the realization of the room-temperature quantum spin Hall edge state in a higher-order topological insulator.
Topological insulator
Topological degeneracy
Cite
Citations (1)
Room-temperature realization of macroscopic quantum phenomena is one of the major pursuits in fundamental physics. The quantum spin Hall state, a topological quantum phenomenon that features a two-dimensional insulating bulk and a helical edge state, has not yet been realized at room temperature. Here, we use scanning tunneling microscopy to visualize a quantum spin Hall edge state on the surface of the higher-order topological insulator Bi4Br4. We find that the atomically resolved lattice exhibits a large insulating gap of over 200meV, and an atomically sharp monolayer step edge hosts a striking in-gap gapless state, suggesting the topological bulk-boundary correspondence. An external magnetic field can gap the edge state, consistent with the time-reversal symmetry protection inherent to the underlying topology. We further identify the geometrical hybridization of such edge states, which not only attests to the Z2 topology of the quantum spin Hall state but also visualizes the building blocks of the higher-order topological insulator phase. Remarkably, both the insulating gap and topological edge state are observed to persist up to 300K. Our results point to the realization of the room-temperature quantum spin Hall edge state in a higher-order topological insulator.
Topological insulator
Topological degeneracy
Cite
Citations (0)
Identification and control of topological phases in topological thin films offer great opportunities for fundamental research and the fabrication of topology-based devices. Here, combining molecular beam epitaxy, angle-resolved photoemission spectroscopy, and ab initio calculations, we investigate the electronic structure evolution in (Bi1-xInx)2Se3 films (0 ≤ x ≤ 1) with thickness from 2 to 13 quintuple layers. By employing both thickness and In substitution as two independent "knobs" to control the gap change, we identify the evolution between several topological phases, i.e., dimensional crossover from a three-dimensional topological insulator to its two-dimensional counterpart with gapped surface state, and topological phase transition from a topological insulator to a normal semiconductor with increasing In concentration. Furthermore, by introducing In substitution, we experimentally demonstrated the trivial topological nature of Bi2Se3 thin films (below 6 quintuple layers) as two-dimensional gapped systems, consistent with our theoretical calculations. Our results provide not only a comprehensive phase diagram of (Bi1-xInx)2Se3 and a route to control its phase evolution but also a practical way to experimentally determine the topological properties of a gapped compound by a topological phase transition and band gap engineering.
Topological insulator
Surface States
Cite
Citations (23)
Abstract As the thickness of a three-dimensional (3D) topological insulator (TI) becomes comparable to the penetration depth of surface states, quantum tunneling between surfaces turns their gapless Dirac electronic structure into a gapped spectrum. Whether the surface hybridization gap can host topological edge states is still an open question. Herein, we provide transport evidence of 2D topological states in the quantum tunneling regime of a bulk insulating 3D TI BiSbTeSe2. Different from its trivial insulating phase, this 2D topological state exhibits a finite longitudinal conductance at ~2e2/h when the Fermi level is aligned within the surface gap, indicating an emergent quantum spin Hall (QSH) state. The transition from the QSH to quantum Hall (QH) state in a transverse magnetic field further supports the existence of this distinguished 2D topological phase. In addition, we demonstrate a second route to realize the 2D topological state via surface gap-closing and topological phase transition mechanism mediated by a transverse electric field. The experimental realization of the 2D topological phase in a 3D TI enriches its phase diagram and marks an important step toward functional topological quantum devices.
Topological insulator
Topological degeneracy
Surface States
Cite
Citations (2)
This chapter begins with a description of quantum spin Hall systems, or topological insulators, which embody a new quantum state of matter theoretically proposed in 2005 and experimentally observed later on using various methods. Topological insulators can be realized in both two dimensions (2D) and in three dimensions (3D), and are nonmagnetic insulators in the bulk that possess gapless edge states (2D) or surface states (3D). These edge/surface states carry pure spin current and are sometimes called helical. The novel property for these edge/surface states is that they originate from bulk topological order, and are robust against nonmagnetic disorder. The following sections then explain how topological insulators are related to other spin-transport phenomena.
Topological insulator
Gapless playback
Surface States
State of matter
Cite
Citations (2)
Topological states of matter originate from distinct topological electronic structures of materials. As for strong topological insulators (STIs), the topological surface (interface) is a direct consequence of electronic structure transition between materials categorized to different topological genus. Therefore, it is fundamentally interesting if such topological character can be manipulated. Besides tuning the crystal field and the strength of spin-orbital coupling (e.g., by external strain, or chemical doping), there is currently rare report on topological state induced in ordinary insulators (OIs) by the heterostructure of OI/STI. Here we report the observation of a Dirac cone topological surface state (TSS) induced on the Sb2Se3 layer up to 15 nm thick in the OI/STI heterostructure, in sharp contrast with the OI/OI heterostructure where no sign of TSS can be observed. This is evident for an induced topological state in an OI by heterostructure.
Topological insulator
Surface States
Topological degeneracy
Cite
Citations (0)
Topological insulator
Topological degeneracy
Gapless playback
Cite
Citations (75)
Topological insulator
Topological degeneracy
Cite
Citations (1)
Topological materials burgeoned with the discovery of the quantum spin Hall insulators (QSHIs). Since their discovery, QSHIs have been viewed as being ${\mathbb{Z}}_{2}$ topological insulators. This commonly held viewpoint, however, hides the far richer nature of the QSHI state. Unlike the ${\mathbb{Z}}_{2}$ topological insulator, which hosts gapless boundary states protected by the time-reversal symmetry, the QSHI does not support gapless edge states because the spin-rotation symmetry breaks down in real systems. Here, we demonstrate that QSHIs hide higher-order topological insulator phases through two exemplar systems. We first consider the Kane-Mele model under an external field and show that it carries an odd spin Chern number ${\mathcal{C}}_{s}=1$. The model is found to host gapless edge states in the absence of Rashba spin-orbit coupling (SOC). But, a gap opens up in the edge spectrum when SOC is included, and the system turns into a higher-order topological insulator with in-gap corner states emerging in the spectrum of a nanodisk. We also discuss a time-reversal symmetric tight-binding model on a square lattice, and show that it carries an even spin Chern number ${\mathcal{C}}_{s}=2$. This unique phase has been taken to be topologically trivial because of its gapped edge spectrum. We show it supports in-gap corner states and hosts a higher-order topological phase.
Topological insulator
Gapless playback
Mott insulator
Lattice (music)
Square lattice
Cite
Citations (5)
From the Contents: Introduction.- Starting from the Dirac equation.- Minimal lattice model for topological insulator.- Topological invariants.- Topological phases in one dimension.- Quantum spin Hall effect.- Three dimensional topological insulators.- Impurities and defects in topological insulators.- Topological superconductors and superfluids.- Majorana fermions in topological insulators.- Topological Anderson Insulator.- Summary: Symmetry and Topological Classification.
Topological insulator
Topological degeneracy
Majorana fermion
Cite
Citations (244)