scholarly journals Direct comparison of current-induced spin polarization in topological insulator Bi2Se3 and InAs Rashba states

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
C. H. Li ◽  
O.M.J. van ‘t Erve ◽  
S. Rajput ◽  
L. Li ◽  
B. T. Jonker
Keyword(s):  
Spin Polarization ◽  
Three Dimensional ◽  
Surface States ◽  
Bias Current ◽  
Band Bending ◽  
Potentiometric Measurements ◽  
Dimensional Electron Gas ◽  
Symmetry Protected ◽  
Electrochemical Potentials ◽  
Spin Momentum

Abstract Three-dimensional topological insulators (TIs) exhibit time-reversal symmetry protected, linearly dispersing Dirac surface states with spin–momentum locking. Band bending at the TI surface may also lead to coexisting trivial two-dimensional electron gas (2DEG) states with parabolic energy dispersion. A bias current is expected to generate spin polarization in both systems, although with different magnitude and sign. Here we compare spin potentiometric measurements of bias current-generated spin polarization in Bi2Se3(111) where Dirac surface states coexist with trivial 2DEG states, and in InAs(001) where only trivial 2DEG states are present. We observe spin polarization arising from spin–momentum locking in both cases, with opposite signs of the measured spin voltage. We present a model based on spin dependent electrochemical potentials to directly derive the sign expected for the Dirac surface states, and show that the dominant contribution to the current-generated spin polarization in the TI is from the Dirac surface states.

scholarly journals Three-Dimensional Topological States of Phonons with Tunable Pseudospin Physics

Research ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
Yizhou Liu ◽  
Yong Xu ◽  
Wenhui Duan
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Surface States ◽  
Phonon Transport ◽  
Efficient Control ◽  
Topological States ◽  
Topological Surface ◽  
Symmetry Protected ◽  
Energy Information ◽  
Crystalline Symmetry

Efficient control of phonons is crucial to energy-information technology, but limited by the lacking of tunable degrees of freedom like charge or spin. Here we suggest to utilize crystalline symmetry-protected pseudospins as new quantum degrees of freedom to manipulate phonons. Remarkably, we reveal a duality between phonon pseudospins and electron spins by presenting Kramers-like degeneracy and pseudospin counterparts of spin-orbit coupling, which lays the foundation for “pseudospin phononics”. Furthermore, we report two types of three-dimensional phononic topological insulators, which give topologically protected, gapless surface states with linear and quadratic band degeneracies, respectively. These topological surface states display unconventional phonon transport behaviors attributed to the unique pseudospin-momentum locking, which are useful for phononic circuits, transistors, antennas, etc. The emerging pseudospin physics offers new opportunities to develop future phononics.

scholarly journals Tunable Topological Surface States of Three-Dimensional Acoustic Crystals

2021 ◽  
Vol 9 ◽  
Author(s):  
Hua-Shan Lai ◽  
Yu-Li Xu ◽  
Bo He ◽  
Xiao-Chen Sun ◽  
Cheng He ◽  
...  
Keyword(s):  
Domain Wall ◽  
Mirror Symmetry ◽  
Three Dimensional ◽  
Surface States ◽  
Building Blocks ◽  
Quantum Spin ◽  
Quantum Spin Hall Effect ◽  
Breaking Mechanism ◽  
Symmetry Protected ◽  
Complete Bandgap

Topological design for band structures of artificial materials such as acoustic crystals provides a powerful tool to manipulate wave propagating in a robust and symmetry-protected way. In this paper, based on the band folding and breaking mechanism by building blocks with acoustic atoms, we construct a three-dimensional topological acoustic crystal with a large complete bandgap. At a mirror-symmetry domain wall, two gapped symmetry and anti-symmetry surface states can be found in the bandgap, originated from two opposite Su-Schrieffer-Heeger chains. Remarkably, by enforcing a glide symmetry on the domain wall, we can tune the original gapped surface states in a gapless fashion at the boundaries of surface Brillouin zone, acting as omnidirectional acoustic quantum spin Hall effect. Our tunable yet straightforward acoustic crystals offer promising potentials in realizing future topological acoustic devices.

scholarly journals Weyl-like points from band inversions of spin-polarised surface states in NbGeSb

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
I. Marković ◽  
C. A. Hooley ◽  
O. J. Clark ◽  
F. Mazzola ◽  
M. D. Watson ◽  
...  
Keyword(s):  
Mirror Symmetry ◽  
Density Functional ◽  
Three Dimensional ◽  
Surface States ◽  
Nodal Line ◽  
Surface Band ◽  
Spin Orbital ◽  
Band Inversion ◽  
Topological Surface ◽  
Symmetry Protected

AbstractBand inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals. Here, we create a band inversion not of bulk states, but rather between manifolds of surface states. We realise this by aliovalent substitution of Nb for Zr and Sb for S in the ZrSiS family of nonsymmorphic semimetals. Using angle-resolved photoemission and density-functional theory, we show how two pairs of surface states, known from ZrSiS, are driven to intersect each other near the Fermi level in NbGeSb, and to develop pronounced spin splittings. We demonstrate how mirror symmetry leads to protected crossing points in the resulting spin-orbital entangled surface band structure, thereby stabilising surface state analogues of three-dimensional Weyl points. More generally, our observations suggest new opportunities for engineering topologically and symmetry-protected states via band inversions of surface states.

scholarly journals Magnetic crystalline-symmetry-protected axion electrodynamics and field-tunable unpinned Dirac cones in EuIn2As2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
S. X. M. Riberolles ◽  
T. V. Trevisan ◽  
B. Kuthanazhi ◽  
T. W. Heitmann ◽  
F. Ye ◽  
...  
Keyword(s):  
Density Functional ◽  
Surface States ◽  
Antiferromagnetic Order ◽  
Functional Theory ◽  
Magnetic Symmetry ◽  
Integer Quantum ◽  
Symmetry Protected ◽  
Topological Crystalline Insulator ◽  
Low Symmetry ◽  
Crystalline Symmetry

AbstractKnowledge of magnetic symmetry is vital for exploiting nontrivial surface states of magnetic topological materials. EuIn2As2 is an excellent example, as it is predicted to have collinear antiferromagnetic order where the magnetic moment direction determines either a topological-crystalline-insulator phase supporting axion electrodynamics or a higher-order-topological-insulator phase with chiral hinge states. Here, we use neutron diffraction, symmetry analysis, and density functional theory results to demonstrate that EuIn2As2 actually exhibits low-symmetry helical antiferromagnetic order which makes it a stoichiometric magnetic topological-crystalline axion insulator protected by the combination of a 180∘ rotation and time-reversal symmetries: $${C}_{2}\times {\mathcal{T}}={2}^{\prime}$$ C 2 × T = 2 ′ . Surfaces protected by $${2}^{\prime}$$ 2 ′ are expected to have an exotic gapless Dirac cone which is unpinned to specific crystal momenta. All other surfaces have gapped Dirac cones and exhibit half-integer quantum anomalous Hall conductivity. We predict that the direction of a modest applied magnetic field of μ0H ≈ 1 to 2 T can tune between gapless and gapped surface states.

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