Double-bowl state in photonic Dirac nodal line semimetal

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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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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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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Topological Semimetals in Square-Net Materials

Annual Review of Materials Research ◽

10.1146/annurev-matsci-070218-010114 ◽

2019 ◽

Vol 49 (1) ◽

pp. 185-206 ◽

Cited By ~ 21

Author(s):

Sebastian Klemenz ◽

Shiming Lei ◽

Leslie M. Schoop

Keyword(s):

Hall Effect ◽

Electronic Properties ◽

Quantum Hall Effect ◽

Quantum Hall ◽

Nodal Line ◽

Topological Properties ◽

Topological Materials ◽

Integer Quantum Hall Effect ◽

Integer Quantum ◽

Topological Semimetals

Many materials crystallize in structure types that feature a square net of atoms. While these compounds can exhibit many different properties, some members of this family are topological materials. Within the square-net-based topological materials, the observed properties are rich, ranging, for example, from nodal-line semimetals to a bulk half-integer quantum Hall effect. Hence, the potential for guided design of topological properties is enormous. Here we provide an overview of the crystallographic and electronic properties of these phases and show how they are linked, with the goal of understanding which square-net materials can be topological, and predict additional examples. We close the review by discussing the experimentally observed electronic properties in this family.

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Coexistence of open and closed type nodal line topological semimetals in two dimensional B2C

Journal of Materials Chemistry C ◽

10.1039/c7tc05095j ◽

2018 ◽

Vol 6 (5) ◽

pp. 1206-1214 ◽

Cited By ~ 25

Author(s):

P. Zhou ◽

Z. S. Ma ◽

L. Z. Sun

Keyword(s):

Nodal Line ◽

Two Dimensional ◽

Nodal Lines ◽

Closed Type ◽

Topological Semimetal ◽

Topological Semimetals

The detection of open and closed type nodal lines in the bilayer topological semimetal B2C on the substrate of Cu(110).

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Observation of a giant mass enhancement in the ultrafast electron dynamics of a topological semimetal

Communications Physics ◽

10.1038/s42005-021-00657-6 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Oliver J. Clark ◽

Friedrich Freyse ◽

Irene Aguilera ◽

Alexander S. Frolov ◽

Andrey M. Ionov ◽

...

Keyword(s):

Band Structure ◽

Surface State ◽

Surface States ◽

Detailed Knowledge ◽

Electron Dynamics ◽

Topological Semimetals ◽

Polarized Surface ◽

Topological Phases Of Matter ◽

Mass Enhancement ◽

Kink Structure

AbstractTopological phases of matter offer exciting possibilities to realize lossless charge and spin information transport on ultrafast time scales. However, this requires detailed knowledge of their nonequilibrium properties. Here, we employ time-, spin- and angle-resolved photoemission to investigate the ultrafast response of the Sb(111) spin-polarized surface state to femtosecond-laser excitation. The surface state exhibits a giant mass enhancement which is observed as a kink structure in its energy-momentum dispersion above the Fermi level. The kink structure, originating from the direct coupling of the surface state to the bulk continuum, is characterized by an abrupt change in the group velocity by ~70%, in agreement with our GW-based band structure calculations. Our observation of this connectivity in the transiently occupied band structure enables the unambiguous experimental verification of the topological nature of the surface state. The influence of bulk-surface coupling is further confirmed by our measurements of the electron dynamics, which show that bulk and surface states behave as a single thermalizing electronic population with distinct contributions from low-k electron-electron and high-k electron-phonon scatterings. These findings are important for future applications of topological semimetals and their excitations in ultrafast spintronics.

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Obvious Surface States Connecting to the Projected Triple Points in NaCl’s Phonon Dispersion

Frontiers in Chemistry ◽

10.3389/fchem.2021.789522 ◽

2021 ◽

Vol 9 ◽

Author(s):

Li Zhang ◽

Fang Fang ◽

Lixin Cheng ◽

Huiming Lin ◽

Kai Wang

Keyword(s):

Computer Technology ◽

Triple Point ◽

First Principles ◽

Phonon Dispersion ◽

Surface States ◽

Theoretical Chemistry ◽

First Principles Calculations ◽

Nodal Lines ◽

Topological Materials ◽

Speed And Accuracy

With the development of computer technology and theoretical chemistry, the speed and accuracy of first-principles calculations have significantly improved. Using first-principles calculations to predict new topological materials is a hot research topic in theoretical and computational chemistry. In this work, we focus on a well-known material, sodium chloride (NaCl), and propose that the triple point (TP), quadratic contact triple point (QCTP), linear and quadratic nodal lines can be found in the phonon dispersion of NaCl with Fm3¯ m type structure. More importantly, we propose that the clear surface states connected to the projected TP and QCTP are visible on the (001) surface. It is hoped that further experimental investigation and verification for these properties as mentioned above.

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Persistent optical gating of a topological insulator

Science Advances ◽

10.1126/sciadv.1500640 ◽

2015 ◽

Vol 1 (9) ◽

pp. e1500640 ◽

Cited By ~ 22

Author(s):

Andrew L. Yeats ◽

Yu Pan ◽

Anthony Richardella ◽

Peter J. Mintun ◽

Nitin Samarth ◽

...

Keyword(s):

Chemical Potential ◽

Surface States ◽

Optical Control ◽

Electronic Systems ◽

Optical Gating ◽

Wide Range ◽

Spin Polarized ◽

Electrostatic Gating ◽

Polarized Surface ◽

Insulating Phase

The spin-polarized surface states of topological insulators (TIs) are attractive for applications in spintronics and quantum computing. A central challenge with these materials is to reliably tune the chemical potential of their electrons with respect to the Dirac point and the bulk bands. We demonstrate persistent, bidirectional optical control of the chemical potential of (Bi,Sb)2Te3thin films grown on SrTiO3. By optically modulating a space-charge layer in the SrTiO3substrates, we induce a persistent field effect in the TI films comparable to electrostatic gating techniques but without additional materials or processing. This enables us to optically pattern arbitrarily shapedp- andn-type regions in a TI, which we subsequently image with scanning photocurrent microscopy. The ability to optically write and erase mesoscopic electronic structures in a TI may aid in the investigation of the unique properties of the topological insulating phase. The gating effect also generalizes to other thin-film materials, suggesting that these phenomena could provide optical control of chemical potential in a wide range of ultrathin electronic systems.

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Kramers nodal line metals

Nature Communications ◽

10.1038/s41467-021-22903-9 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Ying-Ming Xie ◽

Xue-Jian Gao ◽

Xiao Yan Xu ◽

Cheng-Ping Zhang ◽

Jin-Xin Hu ◽

...

Keyword(s):

Time Reversal ◽

Nodal Line ◽

Spin Orbit Coupling ◽

Fermi Surfaces ◽

Nodal Lines ◽

New Class ◽

Topological Materials ◽

Weyl Semimetals ◽

Chiral Crystals ◽

Torus Type

AbstractRecently, it was pointed out that all chiral crystals with spin-orbit coupling (SOC) can be Kramers Weyl semimetals (KWSs) which possess Weyl points pinned at time-reversal invariant momenta. In this work, we show that all achiral non-centrosymmetric materials with SOC can be a new class of topological materials, which we term Kramers nodal line metals (KNLMs). In KNLMs, there are doubly degenerate lines, which we call Kramers nodal lines (KNLs), connecting time-reversal invariant momenta. The KNLs create two types of Fermi surfaces, namely, the spindle torus type and the octdong type. Interestingly, all the electrons on octdong Fermi surfaces are described by two-dimensional massless Dirac Hamiltonians. These materials support quantized optical conductance in thin films. We further show that KNLMs can be regarded as parent states of KWSs. Therefore, we conclude that all non-centrosymmetric metals with SOC are topological, as they can be either KWSs or KNLMs.

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The study of magnetic topological semimetals by first principles calculations

npj Computational Materials ◽

10.1038/s41524-019-0237-5 ◽

2019 ◽

Vol 5 (1) ◽

Cited By ~ 11

Author(s):

Jinyu Zou ◽

Zhuoran He ◽

Gang Xu

Keyword(s):

Surface States ◽

Nodal Line ◽

Future Research ◽

Honeycomb Lattice ◽

Space Groups ◽

Type Iv ◽

Fermi Arcs ◽

Topological Quantum ◽

Recent Developments ◽

Topological Semimetals

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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