scholarly journals Topological crystalline insulator nanostructures

Nanoscale ◽  
2014 ◽  
Vol 6 (23) ◽  
pp. 14133-14140 ◽  
Author(s):  
Jie Shen ◽  
Judy J. Cha
Keyword(s):  
Time Reversal ◽  
Topological Insulators ◽  
Surface States ◽  
Time Reversal Symmetry ◽  
Topological Crystalline Insulators ◽  
Topological Crystalline Insulator ◽  
Crystalline Symmetry

Topological crystalline insulators are topological insulators whose surface states are protected by the crystalline symmetry, instead of the time reversal symmetry.

scholarly journals Phase diagrams of superconducting topological surface states

2021 ◽  
Vol 24 (4) ◽  
pp. 43701
Author(s):  
W. Zhao ◽  
L. Ding ◽  
B. Zhou ◽  
J. Wu ◽  
Y. Bai ◽  
...  
Keyword(s):  
Phase Diagrams ◽  
Time Reversal ◽  
Mirror Symmetry ◽  
Surface States ◽  
Time Reversal Symmetry ◽  
And Topology ◽  
Topological Surface ◽  
Iron Based ◽  
Crystalline Symmetry

In this paper, we present a detailed study on the phase diagrams of superconducting topological surface states, especially, focusing on the interplay between crystalline symmetry and topology of the effective BdG Hamiltonian. We show that for the 4 x 4 kinematic Hamiltonian of the normal state, a mirror symmetry M can be defined, and for the M-odd pairings, the classification of the 8 x 8 BdG Hamiltonian is ℤ⊕ℤ, and the time-reversal symmetry is broken intrinsically. The topological non-trivial phase can support chiral Majorana edge modes, and can be realized in the thin films of iron-based superconductor such as FeSeTe.

scholarly journals Strain-tuning of Dirac states at the SnTe (001) surface

2015 ◽  
Author(s):  
Matthias Drüppel ◽  
Peter Kruger ◽  
Michael Rohlfing
Keyword(s):  
Density Functional Theory ◽  
Time Reversal ◽  
Density Functional ◽  
Displacement Vector ◽  
Surface States ◽  
Functional Theory ◽  
Bulk Properties ◽  
Invariant Points ◽  
Topological Crystalline Insulator ◽  
Crystalline Symmetry

The topological crystalline insulator SnTe belongs to the recently discovered class of materials in which a crystalline symmetry ensures the existence of topologically protected Dirac like surface states. In contrast to topological insulators, this symmetry can be broken via deformations of the crystal. This opens up new possibilities of manipulating the Dirac states and inducing a controllable gap. Here, we have employed density-functional theory to investigate the response of the Dirac states to lattice deformations [1]. The (001) surface exhibits four Dirac cones which lie at non-time-reversal-invariant points close to X, along the projection of the (110) and (110) mirror planes. Our calculations show that a gap of up to approx 30 meV can be introduced via lattice deformations that break at least one of these mirror symmetries. Remarkably, distortions at the surface only can already open up the gap, even though bulk properties are not changed. The gap is formed at either all four or just two cones, depending on the direction of the displacement vector, making it possible to create a state where gaped and non-gaped Dirac cones coexist. Notably, if the whole slab is distorted, bulk bands are being pushed into the gap making the whole system metallic. [1] M. Drüppel et al, Phys. Rev. B 90, 155312 (2014)

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.

scholarly journals Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kyungchan Lee ◽  
Gunnar F. Lange ◽  
Lin-Lin Wang ◽  
Brinda Kuthanazhi ◽  
Thaís V. Trevisan ◽  
...  
Keyword(s):  
Time Reversal ◽  
Topological Insulators ◽  
Dirac Point ◽  
Saddle Points ◽  
Surface States ◽  
Van Hove Singularity ◽  
Space Group ◽  
Topological Materials ◽  
Topological Surface ◽  
Optimal Space

AbstractTime reversal symmetric (TRS) invariant topological insulators (TIs) fullfil a paradigmatic role in the field of topological materials, standing at the origin of its development. Apart from TRS protected strong TIs, it was realized early on that more confounding weak topological insulators (WTI) exist. WTIs depend on translational symmetry and exhibit topological surface states only in certain directions making it significantly more difficult to match the experimental success of strong TIs. We here report on the discovery of a WTI state in RhBi2 that belongs to the optimal space group P$$\bar{1}$$ 1 ¯ , which is the only space group where symmetry indicated eigenvalues enumerate all possible invariants due to absence of additional constraining crystalline symmetries. Our ARPES, DFT calculations, and effective model reveal topological surface states with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity (VHS) along the (100) direction close to the Fermi energy (EF). Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects.

scholarly journals Cubic 3D Chern photonic insulators with orientable large Chern vectors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chiara Devescovi ◽  
Mikel García-Díez ◽  
Iñigo Robredo ◽  
María Blanco de Paz ◽  
Jon Lasa-Alonso ◽  
...  
Keyword(s):  
Time Reversal ◽  
Degrees Of Freedom ◽  
Surface States ◽  
Magnetic Response ◽  
Time Reversal Symmetry ◽  
General Strategy ◽  
Topological Phases ◽  
Magnetization Axis ◽  
Opening Up ◽  
Internal Symmetries

AbstractTime Reversal Symmetry (TRS) broken topological phases provide gapless surface states protected by topology, regardless of additional internal symmetries, spin or valley degrees of freedom. Despite the numerous demonstrations of 2D topological phases, few examples of 3D topological systems with TRS breaking exist. In this article, we devise a general strategy to design 3D Chern insulating (3D CI) cubic photonic crystals in a weakly TRS broken environment with orientable and arbitrarily large Chern vectors. The designs display topologically protected chiral and unidirectional surface states with disjoint equifrequency loops. The resulting crystals present the following characteristics: First, by increasing the Chern number, multiple surface states channels can be supported. Second, the Chern vector can be oriented along any direction simply changing the magnetization axis, opening up larger 3D CI/3D CI interfacing possibilities as compared to 2D. Third, by lowering the TRS breaking requirements, the system is ideal for realistic photonic applications where the magnetic response is weak.

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