Broken-symmetry states in topological insulators

2015 ◽  
Vol 29 (25) ◽  
pp. 1530006
Author(s):  
Yihua Wang
Keyword(s):  
Three Dimensional ◽  
Surface States ◽  
Magnetic Monopoles ◽  
Broken Symmetry ◽  
Metallic Surface ◽  
Photoemission Spectroscopy ◽  
Majorana Fermions ◽  
Magnetic Structures ◽  
Light Pulses ◽  
Fundamental Particles

Breaking the time-reversal symmetry (TRS) on the surface of a three-dimensional topological insulator (TI) transforms its metallic surface into a Chern insulator. The TRS-broken surface states are essential for many exotic emergent particles in condensed matter. In this review, I will show broken TRS surface states of TI induced by magnetism and by light imaged with scanning microscopy and photoemission spectroscopy, respectively. Our capability to manipulate mesoscopic magnetic structures as well as to shape ultrafast light pulses makes broken-symmetry states in TI promising platforms to simulate elusive fundamental particles such as magnetic monopoles and Majorana fermions.

Sodium Doping of Bi/Si(111) Ultra-Thin Films

2014 ◽  
Vol 213 ◽  
pp. 65-70
Author(s):  
Maria V. Ryzhkova ◽  
Dimitry V. Gruznev ◽  
Elena A. Borisenko ◽  
Dmitry A. Tsukanov
Keyword(s):  
Thin Films ◽  
Electrical Conductance ◽  
Surface States ◽  
Surface Conductivity ◽  
Metallic Surface ◽  
Photoemission Spectroscopy ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Sodium Doping ◽  
Reconstructed Surfaces ◽  
Conductance Changes

Changes in electrical conductance of the Bi/Si (111) reconstructed surfaces and Bi {012} or Bi (001) ultra-thin films have been studied after sodium deposition at room temperature. It was observed that deposition of sodium onto Si (111)-β-3×3-Bi surface results in increasing of surface conductivity up to 0.3 monolayers (ML) of adsorbed sodium atoms. These conductance changes were explained by developing of the metallic surface states in the band gap as revealed by angle resolved photoemission spectroscopy spectra. Moreover, it was shown that sodium adsorption onto Bi {012} and Bi (001) thin films leads to drastic changes in its surface conductivity including a peak of maximum electrical conductance at 0.5 monolayers of adsorbed sodium.

scholarly journals Erasable superconductivity in topological insulator Bi2Se3 induced by voltage pulse

2020 ◽  
Author(s):  
Tian Le ◽  
Qikai Ye ◽  
Chufan Chen ◽  
Lichang Yin ◽  
Dongting Zhang ◽  
...  
Keyword(s):  
Topological Insulator ◽  
Voltage Pulse ◽  
Three Dimensional ◽  
Point Contact ◽  
Surface States ◽  
Majorana Fermions ◽  
Base Temperature ◽  
Point Contacts ◽  
Reflection Peak ◽  
Potential Applications

Abstract Three-dimensional topological insulators (TIs) attract much attention due to its topologically protected Dirac surface states. Doping into TIs or their proximity with normal superconductors can promote the realization of topological superconductivity (SC) and Majorana fermions with potential applications in quantum computations. Here, we observed an emergent superconductivity in local mesoscopic point-contacts on the topological insulator Bi2Se3 by applying a voltage pulse through the contacts, evidenced by the Andreev reflection peak in the point-contact spectra and a visible resistance drop in the four-probe electrical resistance measurements. More intriguingly, the superconductivity can be erased with thermal cycles by warming up to high temperatures (300 K) and induced again by the voltage pulse at the base temperature (1.9 K), suggesting a signicance for designing new types of quantum devices. Nematic behaviouris also observed in the superconducting state, similar to the case of CuxBi2Se3 as topological superconductor candidates.

The Coexistence of Superconductivity and Topological Order in the Bi2Se3 Thin Films

Science ◽  
2012 ◽  
Vol 336 (6077) ◽  
pp. 52-55 ◽  
Author(s):  
Mei-Xiao Wang ◽  
Canhua Liu ◽  
Jin-Peng Xu ◽  
Fang Yang ◽  
Lin Miao ◽  
...  
Keyword(s):  
Thin Films ◽  
Three Dimensional ◽  
Surface States ◽  
Scanning Tunneling ◽  
Majorana Fermions ◽  
Topological Order ◽  
Tunneling Microscopy ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Topological Surface ◽  
Quantum Phenomena

Three-dimensional topological insulators (TIs) are characterized by their nontrivial surface states, in which electrons have their spin locked at a right angle to their momentum under the protection of time-reversal symmetry. The topologically ordered phase in TIs does not break any symmetry. The interplay between topological order and symmetry breaking, such as that observed in superconductivity, can lead to new quantum phenomena and devices. We fabricated a superconducting TI/superconductor heterostructure by growing dibismuth triselenide (Bi2Se3) thin films on superconductor niobium diselenide substrate. Using scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we observed the superconducting gap at the Bi2Se3 surface in the regime of Bi2Se3 film thickness where topological surface states form. This observation lays the groundwork for experimentally realizing Majorana fermions in condensed matter physics.

scholarly journals Boundary conductance in macroscopic bismuth crystals

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Woun Kang ◽  
Felix Spathelf ◽  
Benoît Fauqué ◽  
Yuki Fuseya ◽  
Kamran Behnia
Keyword(s):  
Quantum Hall ◽  
Three Dimensional ◽  
Surface States ◽  
Metallic Surface ◽  
Periodically Driven ◽  
Dimensional Boundary ◽  
Intimate Link ◽  
Different Shapes ◽  
The Magnetic Field ◽  
Identical Crystal

AbstractThe interface between a solid and vacuum can become electronically distinct from the bulk. This feature, encountered in the case of quantum Hall effect, has a manifestation in insulators with topologically protected metallic surface states. Non-trivial Berry curvature of the Bloch waves or periodically driven perturbation are known to generate it. Here, by studying the angle-dependent magnetoresistance in prismatic bismuth crystals of different shapes, we detect a robust surface contribution to electric conductivity when the magnetic field is aligned parallel to a two-dimensional boundary between the three-dimensional crystal and vacuum. The effect is absent in antimony, which has an identical crystal symmetry, a similar Fermi surface structure and equally ballistic carriers, but an inverted band symmetry and a topological invariant of opposite sign. Our observation confirms that the boundary interrupting the cyclotron orbits remains metallic in bismuth, which is in agreement with what was predicted by Azbel decades ago. However, the absence of the effect in antimony indicates an intimate link between band symmetry and this boundary conductance.

scholarly journals Boundary conductance protected by topology in macroscopic bismuth crystals

2021 ◽  
Author(s):  
Woun Kang ◽  
Felix Spathelf ◽  
Benoit Fauqué ◽  
Yuki Fuseya ◽  
Kamran Behnia
Keyword(s):  
Quantum Hall ◽  
Three Dimensional ◽  
Surface States ◽  
Metallic Surface ◽  
Periodically Driven ◽  
Dimensional Boundary ◽  
Different Shapes ◽  
The Magnetic Field ◽  
Dimensional Crystal ◽  
Identical Crystal

Abstract The interface between a solid and vacuum can become electronically distinct from the bulk. This feature, encountered in the case of quantum Hall effect, has a manifestation in insulators with topologically protected metallic surface states. Non-trivial Berry curvature of the Bloch waves or periodically driven perturbation are known to generate it. Here, by studying the angle-dependent magnetoresistance in prismatic bismuth crystals of different shapes, we detect a robust surface contribution to electric conductivity when the magnetic field is aligned parallel to a two-dimensional boundary between the three-dimensional crystal and vacuum. The effect is absent in antimony, which has an identical crystal symmetry, a similar Fermi surface structure and equally ballistic carriers, but an inverted band symmetry and a topological invariant of opposite sign. Our observation points to the relevance of band symmetries to survival of metallicity at the boundary interrupting the cyclotron orbits.

scholarly journals Vortex states in an acoustic Weyl crystal with a topological lattice defect

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Qiang Wang ◽  
Yong Ge ◽  
Hong-xiang Sun ◽  
Haoran Xue ◽  
Ding Jia ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Lattice Defect ◽  
Three Dimensional ◽  
Surface States ◽  
Real Space ◽  
Lattice Defects ◽  
One Dimensional ◽  
Topological Features ◽  
Topological Lattice

AbstractCrystalline materials can host topological lattice defects that are robust against local deformations, and such defects can interact in interesting ways with the topological features of the underlying band structure. We design and implement a three dimensional acoustic Weyl metamaterial hosting robust modes bound to a one-dimensional topological lattice defect. The modes are related to topological features of the bulk bands, and carry nonzero orbital angular momentum locked to the direction of propagation. They span a range of axial wavenumbers defined by the projections of two bulk Weyl points to a one-dimensional subspace, in a manner analogous to the formation of Fermi arc surface states. We use acoustic experiments to probe their dispersion relation, orbital angular momentum locked waveguiding, and ability to emit acoustic vortices into free space. These results point to new possibilities for creating and exploiting topological modes in three-dimensional structures through the interplay between band topology in momentum space and topological lattice defects in real space.

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