The study of magnetic topological semimetals by first principles calculations

Abstract Magnetic topological semimetals (TSMs) are topological quantum materials with broken time-reversal symmetry (TRS) and isolated nodal points or lines near the Fermi level. Their topological properties would typically reveal from the bulk-edge correspondence principle as nontrivial surface states such as Fermi arcs or drumhead states, etc. Depending on the degeneracies and distribution of the nodes in the crystal momentum space, TSMs are usually classified into Weyl semimetals (WSMs), Dirac semimetals (DSMs), nodal-line semimetals (NLSMs), triple-point semimetals (TPSMs), etc. In this review article, we present the recent advances of magnetic TSMs from a computational perspective. We first review the early predicted magnetic WSMs such as pyrochlore iridates and HgCr2Se4, as well as the recently proposed Heusler, Kagome layers, and honeycomb lattice WSMs. Then we discuss the recent developments of magnetic DSMs, especially CuMnAs in Type-III and EuCd2As2 in Type-IV magnetic space groups (MSGs). Then we introduce some magnetic NLSMs that are robust against spin–orbit coupling (SOC), namely Fe3GeTe2 and LaCl (LaBr). Finally, we discuss the prospects of magnetic TSMs and the interesting directions for future research.

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

npj Computational Materials ◽

10.1038/s41524-021-00672-9 ◽

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.

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Topological semimetal in honeycomb lattice LnSI

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1713261114 ◽

2017 ◽

Vol 114 (40) ◽

pp. 10596-10600 ◽

Cited By ~ 13

Author(s):

Simin Nie ◽

Gang Xu ◽

Fritz B. Prinz ◽

Shou-cheng Zhang

Keyword(s):

Condensed Matter ◽

Surface States ◽

Nodal Line ◽

Honeycomb Lattice ◽

Nodal Lines ◽

Weyl Semimetal ◽

The Standard Model ◽

Weyl Semimetals ◽

Topological Semimetals ◽

The Right

Recognized as elementary particles in the standard model, Weyl fermions in condensed matter have received growing attention. However, most of the previously reported Weyl semimetals exhibit rather complicated electronic structures that, in turn, may have raised questions regarding the underlying physics. Here, we report promising topological phases that can be realized in specific honeycomb lattices, including ideal Weyl semimetal structures, 3D strong topological insulators, and nodal-line semimetal configurations. In particular, we highlight a semimetal featuring both Weyl nodes and nodal lines. Guided by this model, we showed that GdSI, the long-perceived ideal Weyl semimetal, has two pairs of Weyl nodes residing at the Fermi level and that LuSI (YSI) is a 3D strong topological insulator with the right-handed helical surface states. Our work provides a mechanism to study topological semimetals and proposes a platform for exploring the physics of Weyl semimetals as well as related device designs.

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Are the surface Fermi arcs in Dirac semimetals topologically protected?

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1524787113 ◽

2016 ◽

Vol 113 (31) ◽

pp. 8648-8652 ◽

Cited By ~ 67

Author(s):

Mehdi Kargarian ◽

Mohit Randeria ◽

Yuan-Ming Lu

Keyword(s):

Chemical Potential ◽

Surface States ◽

Quantum Oscillation ◽

Band Model ◽

Fermi Surfaces ◽

Space Groups ◽

Angle Resolved Photoemission Spectroscopy ◽

Fermi Arcs ◽

Anomalous Surface ◽

Dirac Semimetals

Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k=(0,0,±Q), where gapless states on the side surfaces are protected only near kz=0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.

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Magnetism-induced topological transition in EuAs3

10.21203/rs.3.rs-100461/v1 ◽

2020 ◽

Author(s):

Erjian Cheng ◽

Wei Xia ◽

Jie Xu ◽

Chengwei Wang ◽

Chuanying Xi ◽

...

Keyword(s):

Electrical Transport ◽

Berry Phase ◽

Magnetic Moments ◽

Surface States ◽

Nodal Line ◽

Chiral Anomaly ◽

Topological Transition ◽

Spin Polarized ◽

Exotic Physics ◽

Topological Semimetals

Abstract The nature of the interaction between magnetism and topology in magnetic topological semimetals remains mysterious, but may be expected to lead to a variety of novel physics. We present ab initio band calculations, electrical transport and angle-resolved photoemission spectroscopy (ARPES) measurements on the magnetic semimetal EuAs3, demonstrating a magnetism-induced topological transition from a topological nodal-line semimetal in the paramagnetic or the spin-polarized state to a topological massive Dirac metal in the antiferromagnetic (AFM) ground state at low temperature, featuring a pair of massive Dirac points, inverted bands and topological surface states on the (010) surface. Shubnikov-de Haas (SdH) oscillations in the AFM state identify nonzero Berry phase and a negative longitudinal magnetoresistance (n-LMR) induced by the chiral anomaly, confirming the topological nature predicted by band calculations. When magnetic moments are fully polarized by an external magnetic field, an unsaturated and extremely large magnetoresistance (XMR) of ∼ 2×105 % at 1.8 K and 28.3 T is observed, likely arising from topological protection. Consistent with band calculations for the spin-polarized state, four new bands in quantum oscillations different from those in the AFM state are discerned, of which two are topologically protected. Nodal-line structures at the Y point in the Brillouin zone (BZ) are proposed in both the spin-polarized and paramagnetic states, and the latter is proven by ARPES. Moreover, a temperature-induced Lifshitz transition accompanied by the emergence of a new band below 3 K is revealed. These results indicate that magnetic EuAs3 provides a rich platform to explore exotic physics arising from the interaction of magnetism with topology.

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Double-bowl state in photonic Dirac nodal line semimetal

Light Science & Applications ◽

10.1038/s41377-021-00614-6 ◽

2021 ◽

Vol 10 (1) ◽

Author(s):

Mengying Hu ◽

Ye Zhang ◽

Xi Jiang ◽

Tong Qiao ◽

Qiang Wang ◽

...

Keyword(s):

Surface States ◽

Nodal Line ◽

Electronic Systems ◽

Nodal Lines ◽

Spectrum Range ◽

The Past ◽

Topological Materials ◽

Classical Waves ◽

Topological Semimetals ◽

Polarized Surface

AbstractThe past decade has seen a proliferation of topological materials for both insulators and semimetals in electronic systems and classical waves. Topological semimetals exhibit topologically protected band degeneracies, such as nodal points and nodal lines. Dirac nodal line semimetals (DNLS), which own four-fold line degeneracy, have drawn particular attention. DNLSs have been studied in electronic systems but there is no photonic DNLS. Here in this work, we provide a new mechanism, which is unique for photonic systems to investigate a stringent photonic DNLS. When truncated, the photonic DNLS exhibits double-bowl states (DBS), which comprise two sets of perpendicularly polarized surface states. In sharp contrast to nondegenerate surface states in other photonic systems, here the two sets of surface states are almost degenerate over the whole-spectrum range. The DBS and the bulk Dirac nodal ring (DNR) dispersion along the relevant directions, are experimentally resolved.

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Refined symmetry indicators for topological superconductors in all space groups

Science Advances ◽

10.1126/sciadv.aaz8367 ◽

2020 ◽

Vol 6 (18) ◽

pp. eaaz8367 ◽

Cited By ~ 5

Author(s):

Seishiro Ono ◽

Hoi Chun Po ◽

Haruki Watanabe

Keyword(s):

Order Parameter ◽

Surface States ◽

Topological Invariants ◽

Inversion Symmetry ◽

Fermi Surfaces ◽

Space Groups ◽

Guiding Principle ◽

Topological Superconductors ◽

Topological Quantum ◽

Topological Quantum Computation

Topological superconductors are exotic phases of matter featuring robust surface states that could be leveraged for topological quantum computation. A useful guiding principle for the search of topological superconductors is to relate the topological invariants with the behavior of the pairing order parameter on the normal-state Fermi surfaces. The existing formulas, however, become inadequate for the prediction of the recently proposed classes of topological crystalline superconductors. In this work, we advance the theory of symmetry indicators for topological (crystalline) superconductors to cover all space groups. Our main result is the exhaustive computation of the indicator groups for superconductors under a variety of symmetry settings. We further illustrate the power of this approach by analyzing fourfold symmetric superconductors with or without inversion symmetry and show that the indicators can diagnose topological superconductors with surface states of different dimensionalities or dictate gaplessness in the bulk excitation spectrum.

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Coexistence of type-II and type-IV Dirac fermions in SrAgBi

Modern Physics Letters B ◽

10.1142/s0217984921501815 ◽

2021 ◽

pp. 2150181

Author(s):

Tian-Chi Ma ◽

Jing-Nan Hu ◽

Yuan Chen ◽

Lei Shao ◽

Xian-Ru Hu ◽

...

Keyword(s):

High Energy Physics ◽

Surface States ◽

High Energy ◽

Dirac Fermion ◽

Dirac Fermions ◽

Type Ii ◽

Linear Dispersion ◽

Space Groups ◽

Type Iv ◽

Poincaré Symmetry

Relativistic massless Weyl and Dirac fermions have isotropic and linear dispersion relations to maintain Poincaré symmetry, which is the most basic symmetry in high-energy physics. The situation in condensed matter physics is less constrained; only certain subgroups of Poincaré symmetry — the 230 space groups that exist in 3D lattices — need be respected. Then, the free fermionic excitations that have no high-energy analogues could exist in solid state systems. Here, We discovered a type of nonlinear Dirac fermion without high-energy analogue in SrAgBi and named it type-IV Dirac fermion. The type-IV Dirac fermion has a nonlinear dispersion relationship and is similar to the type-II Dirac fermion, which has electron pocket and hole pocket. The effective model for the type-IV Dirac fermion is also found. It is worth pointing out that there is a type-II Dirac fermion near this new Dirac fermion. So we used two models to describe the coexistence of these two Dirac fermions. Topological surface states of these two Dirac points are also calculated. We envision that our findings will stimulate researchers to study novel physics of type-IV Dirac fermions, as well as the interplay of type-II and type-IV Dirac fermions.

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Computation and data driven discovery of topological phononic materials

Nature Communications ◽

10.1038/s41467-021-21293-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jiangxu Li ◽

Jiaxi Liu ◽

Stanley A. Baronett ◽

Mingfeng Liu ◽

Lei Wang ◽

...

Keyword(s):

High Throughput Screening ◽

Electronic System ◽

Nodal Line ◽

Data Driven ◽

Single Type ◽

Type I ◽

Structure Property ◽

Topological Quantum ◽

Data Driven Approach ◽

Spin Electronic

AbstractThe discovery of topological quantum states marks a new chapter in both condensed matter physics and materials sciences. By analogy to spin electronic system, topological concepts have been extended into phonons, boosting the birth of topological phononics (TPs). Here, we present a high-throughput screening and data-driven approach to compute and evaluate TPs among over 10,000 real materials. We have discovered 5014 TP materials and grouped them into two main classes of Weyl and nodal-line (ring) TPs. We have clarified the physical mechanism for the occurrence of single Weyl, high degenerate Weyl, individual nodal-line (ring), nodal-link, nodal-chain, and nodal-net TPs in various materials and their mutual correlations. Among the phononic systems, we have predicted the hourglass nodal net TPs in TeO3, as well as the clean and single type-I Weyl TPs between the acoustic and optical branches in half-Heusler LiCaAs. In addition, we found that different types of TPs can coexist in many materials (such as ScZn). Their potential applications and experimental detections have been discussed. This work substantially increases the amount of TP materials, which enables an in-depth investigation of their structure-property relations and opens new avenues for future device design related to TPs.

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An approach to emerging optical and optoelectronic applications based on NiO micro- and nanostructures

Nanophotonics ◽

10.1515/nanoph-2021-0041 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

María Taeño ◽

David Maestre ◽

Ana Cremades

Keyword(s):

Gas Sensors ◽

High Frequency ◽

Future Research ◽

Electrochromic Devices ◽

Fuel Cell Electrodes ◽

Magnetic Devices ◽

Optical Microresonators ◽

Optical Limiters ◽

Recent Developments ◽

Potential Applicability

Abstract Nickel oxide (NiO) is one of the very few p-type semiconducting oxides, the study of which is gaining increasing attention in recent years due to its potential applicability in many emerging fields of technological research. Actually, a growing number of scientific works focus on NiO-based electrochromic devices, high-frequency spintronics, fuel cell electrodes, supercapacitors, photocatalyst, chemical/gas sensors, or magnetic devices, among others. However, less has been done so far in the development of NiO-based optical devices, a field in which this versatile transition metal oxide still lags in performance despite its potential applicability. This review could contribute with novelty and new forefront insights on NiO micro and nanostructures with promising applicability in optical and optoelectronic devices. As some examples, NiO lighting devices, optical microresonators, waveguides, optical limiters, and neuromorphic applications are reviewed and analyzed in this work. These emerging functionalities, together with some other recent developments based on NiO micro and nanostructures, can open a new field of research based on this p-type material which still remains scarcely explored from an optical perspective, and would pave the way to future research and scientific advances.

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Metaphor Research and the Hebrew Bible

Currents in Biblical Research ◽

10.1177/1476993x20987952 ◽

2021 ◽

Vol 19 (3) ◽

pp. 235-285

Author(s):

Mason D. Lancaster

Keyword(s):

Hebrew Bible ◽

Conceptual Metaphor ◽

Future Research ◽

Conceptual Metaphor Theory ◽

Current Trends ◽

Metaphor Theory ◽

Recent Developments

This article provides an overview of metaphor theories and research on their own terms, as well as their use in Hebrew Bible (HB) studies. Though metaphor studies in the HB have become increasingly popular, they often draw upon a limited or dated subset of metaphor scholarship. The first half of this article surveys a wide variety of metaphor scholarship from the humanities (philosophical, poetic, rhetorical) and the sciences (e.g., conceptual metaphor theory), beginning with Aristotle but focusing on more recent developments. The second half overviews studies of metaphor in the HB since 1980, surveying works focused on theory and method; works focused on specific biblical books or metaphor domains; and finally noting current trends and suggesting areas for future research.

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