Eightfold fermionic excitation in a charge density wave compound

Zhang, Xi; Gu, Qiangqiang; Sun, Huanhuan; Luo, Tianchuang; Liu, Yanzhao; Chen, Yueyuan; Shao, Zhibin; Zhang, Zongyuan; Li, Shaojian; Sun, Yuanwei; Li, Yuehui; Li, Xiaokang; Xue, Shangjie; Ge, Jun‐Yi; Xing, Ying; Comin, Riccardo; Zhu, Zengwei; Gao, Peng; Yan, Binghai; Feng, Ji; Pan, Minghu; Wang, Jian

doi:10.1103/physrevb.102.035125

Cited by 27 publications

(19 citation statements)

References 54 publications

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“…[133] are complementary to and in complete agreement with the results of this work. Recently, a stable DDP and topological stepedge modes were experimentally measured in the CDW phase of the T -symmetric Dirac semimetal TaTe 4 [132], providing further support for the analysis performed in this work. Additionally, recently, an analysis of minimal Weyl-CDWs beyond mean-field theory was performed in [113]; the analysis in [113] explicitly confirms our characterization of the mean-field QAH and oQAH phases of Weyl-CDWs.…”

supporting

confidence: 79%

“…Specifically, a CDW can fold four WPs in a rotation-and Tsymmetric WSM into an eightfold double Dirac point (DDP) in which line defects bind helical modes equivalent to HOTI hinge states [125,126]; alternatively, a DDP critical point can also be realized by coupling two fourfold Dirac points with a CDW. Recent experiments have demonstrated hinge-statelike step-edge helical modes and robust edge supercurrents in rotation-and T -symmetric WSMs [127][128][129][130][131], as well as a stable DDP and topological step-edge modes in the CDW phase of TaTe 4 [132]. In the SM, we present an explicit model demonstrating that a T -symmetric Dirac-CDW hosts an eightfold DDP critical point that separates weak TI (WTI) and "obstructed" WTI (oWTI) phases that differ by a helical HOTI.…”

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confidence: 99%

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Axionic band topology in inversion-symmetric Weyl-charge-density waves

Wieder

Lin

Bradlyn

2020

Phys. Rev. Research

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In recent theoretical and experimental investigations, researchers have linked the low-energy field theory of a Weyl semimetal gapped with a charge-density wave (CDW) to high-energy theories with axion electrodynamics. However, it remains an open question whether a lattice regularization of the dynamical Weyl-CDW is in fact a single-particle axion insulator (AXI). In this Rapid Communication, we use analytic and numerical methods to study both lattice-commensurate and incommensurate minimal (magnetic) Weyl-CDW phases in the mean-field state. We observe that, as previously predicted from field theory, the two inversion (I)-symmetric Weyl-CDWs with φ = 0, π differ by a topological axion angle δθ φ = π. However, we crucially discover that neither of the minimal Weyl-CDW phases at φ = 0, π is individually an AXI; they are instead quantum anomalous Hall (QAH) and "obstructed" QAH insulators that differ by a fractional translation in the modulated cell, analogous to the two phases of the Su-Schrieffer-Heeger model of polyacetylene. Using symmetry indicators of band topology and non-Abelian Berry phase, we demonstrate that our results generalize to multiband systems with only two Weyl fermions, establishing that minimal Weyl-CDWs unavoidably carry nontrivial Chern numbers that prevent the observation of a static magnetoelectric response. We discuss the experimental implications of our findings and provide models and analysis generalizing our results to nonmagnetic Weyl-and Dirac-CDWs.

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supporting

confidence: 79%

mentioning

confidence: 99%

Axionic band topology in inversion-symmetric Weyl-charge-density waves

Wieder

Lin

Bradlyn

2020

Phys. Rev. Research

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“…On the other hand, CDW orderings in topological semimetals have also attracted considerable interest recently [15,16]. Topological semimetals are special types of semimetals, exhibiting low-energy excitations that are analogous to high-energy elementary particles [17].…”

Section: Introductionmentioning

confidence: 99%

Charge density wave and weak Kondo effect in a Dirac semimetal CeSbTe

Fang

et al. 2021

Sci. China Phys. Mech. Astron.

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Using angle-resolved photoemission spectroscopy (ARPES) and low-energy electron diffraction (LEED), together with densityfunctional theory (DFT) calculation, we report the formation of charge density wave (CDW) and its interplay with the Kondo effect and topological states in CeSbTe. The observed Fermi surface (FS) exhibits parallel segments that can be well connected by the observed CDW ordering vector, indicating that the CDW order is driven by the electron-phonon coupling (EPC) as a result of the nested FS. The CDW gap is large (~0.3 eV) and momentum-dependent, which naturally explains the robust CDW order up to high temperatures. The gap opening leads to a reduced density of states (DOS) near the Fermi level (E F ), which correspondingly suppresses the many-body Kondo effect, leading to very localized 4f electrons at 20 K and above. The topological Dirac cone at the X point is found to remain gapless inside the CDW phase. Our results provide evidence for the competition between CDW and the Kondo effect in a Kondo lattice system. The robust CDW order in CeSbTe and related compounds provide an opportunity to search for the long-sought-after axionic insulator.

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“…Dirac and Weyl fermions are well-studied in many topological semimetals and topological metals [5][6][7][8][9][10] and their nodal points are 4-and 2-fold degenerated band crossing points, respectively. Condensed matter systems can also contain novel fermions without counterparts in high energy physics, such as 3-, 6-, and 8-fold excitations [11][12][13][14][15] due to fewer constraints placed by the space group symmetries. However, topological materials with unconventional 6-and 8-fold fermionic excitations under crystalline symmetry are rarely studied.…”

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confidence: 99%

Coexistence of phononic sixfold, fourfold, and threefold excitations in the ternary antimonide Zr3Ni3Sb4

et al. 2021

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Three-, four-, and six-fold excitations have significantly extended the subjects of condensed matter physics. There is an urgent need for a realistic material that can have coexisting 3-, 4-, and 6-fold excitations. However, these materials are uncommon because these excitations in electronic systems are usually broken by spin-orbit coupling (SOC) and normally far from the Fermi level. Unlike the case in electronic systems, the phonon systems with negligible SOC effect, not constrained by the Pauli exclusion principle, provide a feasible platform to realize these excitations in a wide frequency range. Hence, in this work, we demonstrate by first-principle calculations and symmetry analysis that perfect 3-, 4-, 6fold excitations appear in the phonon dispersion rather than the band structures of Zr 3 Ni 3 Sb 4 , which is a well-known indirect-gap semiconductor with an Y 3 Au 3 Sb 4 -type structure. This material features 3-fold quadratic contact triple-point phonon, 4-fold Dirac point phonon, and 6-fold point phonon. Moreover, these nodal-point phonons are very robust to uniform strain. Two obvious phonon surface arcs of the [001] plane are extended in the whole Brillouin zone, which will facilitate their detection in future experimental studies. The current work provides an ideal model to investigate the rich excitations in a single material.

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Eightfold fermionic excitation in a charge density wave compound

Cited by 27 publications

References 54 publications

Axionic band topology in inversion-symmetric Weyl-charge-density waves

Axionic band topology in inversion-symmetric Weyl-charge-density waves

Charge density wave and weak Kondo effect in a Dirac semimetal CeSbTe

Coexistence of phononic sixfold, fourfold, and threefold excitations in the ternary antimonide Zr3Ni3Sb4

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