scholarly journals Chiral-symmetry protected exceptional torus in correlated nodal-line semimetals

2019 ◽  
Vol 100 (11) ◽  
Author(s):  
Kazuhiro Kimura ◽  
Tsuneya Yoshida ◽  
Norio Kawakami
Keyword(s):  
Chiral Symmetry ◽  
Nodal Line ◽  
Symmetry Protected

Robust topological nodal lines in halide carbides

2019 ◽  
Vol 21 (36) ◽  
pp. 20262-20268 ◽  
Author(s):  
Anh Pham ◽  
Frank Klose ◽  
Sean Li
Keyword(s):  
Nodal Line ◽  
Nodal Lines ◽  
Symmetry Protected ◽  
2D And 3D

This study predicts the existence of a symmetry protected nodal line state in Y2C2I2 in both 2D and 3D.

scholarly journals Multiple Dirac nodes and symmetry protected Dirac nodal line in orthorhombic α -RhSi

2020 ◽  
Vol 102 (11) ◽  
Author(s):  
Shirin Mozaffari ◽  
Niraj Aryal ◽  
Rico Schönemann ◽  
Kuan-Wen Chen ◽  
Wenkai Zheng ◽  
...  
Keyword(s):  
Nodal Line ◽  
Symmetry Protected

A nonsymmorphic-symmetry-protected hourglass Weyl node, hybrid Weyl node, nodal surface, and Dirac nodal line in Pd4X (X = S, Se) compounds

2020 ◽  
Vol 22 (39) ◽  
pp. 22399-22407
Author(s):  
Weizhen Meng ◽  
Ying Liu ◽  
Xiaoming Zhang ◽  
Xuefang Dai ◽  
Guodong Liu
Keyword(s):  
Nodal Line ◽  
Nodal Surface ◽  
Topological Semimetals ◽  
Symmetry Protected

Nonsymmorphic symmetry has been proved to protect band crossings in topological semimetals/metals.

Pressure induced nodal line semimetal in YH3

2020 ◽  
Vol 75 (11) ◽  
pp. 971-979
Author(s):  
Fei-Hu Liu ◽  
Li-Na Wu ◽  
Ying-Hua Deng ◽  
Wei Fu
Keyword(s):  
Mirror Symmetry ◽  
Nodal Line ◽  
First Principle ◽  
Spin Orbital ◽  
Berry's Phase ◽  
Principle Calculation ◽  
Berry’S Phase ◽  
First Principle Calculation ◽  
Topological Constraints ◽  
Symmetry Protected

AbstractThe electronic structure of yttrium trihydride (YH3) under pressure has been explored by using the first-principle calculation. The existence of semiconductor phase of YH3 is predicted at low pressure with symmetry group $p\overline{3}c1$ (165). In the range of 10–24 GPa, electron- and hole-like bands near the Fermi level are overlapped and form a snake-like nodal ring around Γ point. Different from previous literature (D. Shao, T. Chen, Q. Gu, et al., “Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH3,” Sci. Rep., vol. 8, 2018.; J. Wang, Y. Liu, K.-H. Jin, et al., Phys. Rev. B, vol. 98, p. 201112, 2018), which assumes the band degeneracy is protected by mirror symmetry, we argue that the nodal line is protected by the space inversion symmetry and the time reversal symmetry. For weak spin-orbital coupling (SOC), the fermion modes at the band crossings are real 3D Majorana fermions. This is a typical double charged nodal-line semimetal, meaning that there are two topological invariants of this nodal line: a 1D Berry’s phase and a Z2 monopole charge, which are related to the first and the second Stiefel-Whitney classes of the Berry bundle and can be given by the first-principle calculation. It turns out that the 1D Berry’s phase is nontrivial, but the Z2 monopole charge is trivial. Therefore, this nodal line can shrink to a point and gapped out without breaking the topological constraints.

scholarly journals Different types of spin currents in the comprehensive materials database of nonmagnetic spin Hall effect

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Yang Zhang ◽  
Qiunan Xu ◽  
Klaus Koepernik ◽  
Roman Rezaev ◽  
Oleg Janson ◽  
...  
Keyword(s):  
Hall Effect ◽  
Mirror Symmetry ◽  
Spin Current ◽  
Strong Relationship ◽  
Nodal Line ◽  
Spin Hall Effect ◽  
Spin Currents ◽  
Different Types ◽  
Symmetry Protected ◽  
Crystalline Symmetry

AbstractSpin Hall effect (SHE) has its special position in spintronics. To gain new insight into SHE and to identify materials with substantial spin Hall conductivity (SHC), we performed high-precision high-throughput ab initio calculations of the intrinsic SHC for over 20,000 nonmagnetic crystals. The calculations revealed a strong relationship between the magnitude of the SHC and the crystalline symmetry, where a large SHC is typically associated with mirror symmetry-protected nodal line band structures. This database includes 11 materials with an SHC comparable to or even larger than that of Pt. Materials with different types of spin currents were additionally identified. Furthermore, we found that different types of spin current can be obtained by rotating applied electrical fields. This improves our understanding and is expected to facilitate the design of new types of spin-orbitronic devices.

scholarly journals Defective edge states and anomalous bulk-boundary correspondence for topological insulators under non-Hermitian similarity transformation

2020 ◽  
Vol 34 (09) ◽  
pp. 2050146
Author(s):  
C. Wang ◽  
X.-R. Wang ◽  
C.-X. Guo ◽  
S.-P. Kou
Keyword(s):  
Chiral Symmetry ◽  
Topological Insulators ◽  
Skin Effect ◽  
Similarity Transformation ◽  
Topological Invariant ◽  
Inversion Symmetry ◽  
Edge States ◽  
Boundary Correspondence ◽  
Zhang Model ◽  
Symmetry Protected

It was known that for non-Hermitian topological systems due to the non-Hermitian skin effect, the bulk-edge correspondence is broken down. In this paper, by using one-dimensional Su–Schrieffer–Heeger model and two-dimensional (deformed) Qi–Wu–Zhang model as examples, the focus is on a special type of non-Hermitian topological system without non-Hermitian skin effect — topological systems under non-Hermitian similarity transformation. In these non-Hermitian systems, the defective edge states and the breakdown of bulk-edge correspondence are discovered. To characterize the topological properties, a new type of inversion symmetry-protected topological invariant — total [Formula: see text] topological invariant — has been introduced. In topological phases, defective edge states appear. With the help of the effective edge Hamiltonian, it was found that the defective edge states are protected by (generalized) chiral symmetry and thus the (singular) defective edge states are unstable against the perturbation breaking the chiral symmetry. In addition, the results are generalized to non-Hermitian topological insulators with inversion symmetry in higher dimensions. This work could help people to understand the defective edge states and the breakdown of bulk-edge correspondence for non-Hermitian topological systems.

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 Glide symmetry protected higher-order topological insulators from semimetals with butterfly-like nodal lines

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Xiaoting Zhou ◽  
Chuang-Han Hsu ◽  
Cheng-Yi Huang ◽  
Mikel Iraola ◽  
Juan L. Mañes ◽  
...  
Keyword(s):  
Topological Insulator ◽  
Topological Insulators ◽  
Surface States ◽  
Nodal Line ◽  
Higher Order ◽  
Dirac Fermion ◽  
Space Groups ◽  
Nodal Lines ◽  
Topological Semimetals ◽  
Symmetry Protected

AbstractMost topological insulators (TIs) discovered today in spinful systems can be transformed from topological semimetals (TSMs) with vanishing bulk gap via introducing the spin-orbit coupling (SOC), which manifests the intrinsic links between the gapped topological insulator phases and the gapless TSMs. Recently, we have discovered a family of TSMs in time-reversal invariant spinless systems, which host butterfly-like nodal-lines (NLs) consisting of a pair of identical concentric intersecting coplanar ellipses (CICE). In this Communication, we unveil the intrinsic link between this exotic class of nodal-line semimetals (NLSMs) and a $${{\mathbb{Z}}}_{4}$$ Z 4 = 2 topological crystalline insulator (TCI), by including substantial SOC. We demonstrate that in three space groups (i.e., Pbam (No.55), P4/mbm (No.127), and P42/mbc (No.135)), the TCI supports a fourfold Dirac fermion on the (001) surface protected by two glide symmetries, which originates from the intertwined drumhead surface states of the CICE NLs. The higher order topology is further demonstrated by the emergence of one-dimensional helical hinge states, indicating the discovery of a higher order topological insulator protected by a glide symmetry.

scholarly journals Nonsymmorphic-symmetry-protected hourglass Dirac loop, nodal line, and Dirac point in bulk and monolayer X3SiTe6 ( X = Ta, Nb)

2018 ◽  
Vol 97 (4) ◽  
Author(s):  
Si Li ◽  
Ying Liu ◽  
Shan-Shan Wang ◽  
Zhi-Ming Yu ◽  
Shan Guan ◽  
...  
Keyword(s):  
Dirac Point ◽  
Nodal Line ◽  
Symmetry Protected
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