Symmetry demanded topological nodal-line materials

Yang, Shuo-Ying; Yang, Hao; Derunova, Elena; Parkin, Stuart S. P.; Yan, Binghai; Ali, Mazhar N.

doi:10.1080/23746149.2017.1414631

Cited by 204 publications

(177 citation statements)

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“…In general, NLSMs without SOC will transform into either insulators, DSMs, WSMs or even double NLSMs when SOC is considered, which is much related to the symmetries in the corresponding systems. 56 While in this work, when SOC is included, the three nodal lines around Γ point will be gapped out with a small gap (≈ 5 meV), making YH 3 a topological insulator with Z 2 =(1,000). Nevertheless, further calculation shows that the gap induced by SOC along the nodal ring is very small (about 5 meV), which indicates that the effect of SOC is negligible and the characteristic of the nodal ring can be preserved.…”

Section: Introductionmentioning

confidence: 92%

Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH3

Shao

Chen

et al. 2018

Sci Rep

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Using ab initio calculations based on density-functional theory and effective model analysis, we propose that the trigonal YH3 (Space Group: Pc1) at ambient pressure is a node-line semimetal when spin-orbit coupling (SOC) is ignored. This trigonal YH3 has very clean electronic structure near Fermi level and its nodal lines locate very closely to the Fermi energy, which makes it a perfect system for model analysis. Symmetry analysis shows that the nodal ring in this compound is protected by the glide-plane symmetry, where the band inversion of |Y+, dxz〉 and |H1−, s〉 orbits at Γ point is responsible for the formation of the nodal lines. When SOC is included, the line nodes are prohibited by the glide-plane symmetry, and a small gap (≈5 meV) appears, which leads YH3 to be a strong topological insulator with Z2 indices (1,000). Thus the glide-plane symmetry plays an opposite role in the formation of the nodal lines in cases without and with SOC. As the SOC-induced gap is so small that can be neglected, this Pc1 YH3 may be a good candidate for experimental explorations on the fundamental physics of topological node-line semimetals. We find the surface states of this Pc1 phase are somehow unique and may be helpful to identify the real ground state of YH3 in the experiment.

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Section: Introductionmentioning

confidence: 92%

Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH3

Shao

Chen

et al. 2018

Sci Rep

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“…24 We should mention that CaAgAs and CaAgP have been predicted to be NLSMs as well, 21 and although the electronic structure has not yet been confirmed, some typical transport phenomena have been observed in CaAgAs. 107 NLSMs have recently been reviewed by Ali et al 105 and thus we refer the reader to this reference for further detailed descriptions of the crystal and electronic structures of these materials.…”

Section: Weyl Semimetalsmentioning

confidence: 99%

Chemical Principles of Topological Semimetals

2018

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PrefaceThe recent rapid development in the field of topological materials raises expectations that these materials might allow solving a large variety of current challenges in condensed matter science, ranging from applications in quantum computing, to infra-red sensors or heterogenous catalysis. 1-8 In addition, exciting predictions of completely new physical phenomena that could arise in topological materials drive the interest in these compounds. 9,10 For example, charge carriers might behave completely different from what we expect from the current laws of physics if they travel through topologically non-trivial systems. 11,12 This happens because charge carriers in topological materials can be different from the normal type of fermions we know, which in turn affects the transport properties of the material. It has also been proposed that we could even find "new fermions", i.e. fermions that are different from the types we currently know in condensed matter systems as well as in particle physics. 10 Such proposals connect the fields of high energy or particle physics, whose goal it is to understand the universe and all the particles it is composed of, with condensed matter physics, 1 arXiv:1804.10649v1 [cond-mat.mtrl-sci] 27 Apr 2018where the same type, or even additional types, of particles can be found as so-called quasiparticles, meaning that the charge carriers behave in a similar way as it would be expected from a certain particle existing in free space.The field of topology in condensed matter physics evolved from the idea that there can be insulators whose band structure is fundamentally different (i.e. has a different topology) from that of the common insulators we know. If two insulators with different topologies are brought into contact, electrons that have no mass and cannot be back scattered are supposed to appear at the interface. These edge states also appear if a topological insulator (TI) is in contact with air, a trivial insulator. 2D TIs have conducting edge states whereas 3D TIs, which were discovered later, have conducting surface states. TIs have already been reviewed multiple times, [13][14][15][16] which is why we focus here on the newer kind of topological materials, namely topological semimetals (TSMs). Nevertheless, we will refer to TIs and their properties where relevant in the context of topological materials and to contrast them with TSMs.The term "topological semimetal" is widely used and basically includes all semimetals that exhibit some non-trivial band topology. We will describe in more detail later in this review what non-trivial topology actually means. Since TSMs are semimetals they are characterized by a gap-less band structure, i.e. they differ from normal metals by being charge balanced, meaning the amount of electrons and holes contributing to their conductivity is exactly the same. Or, phrased differently, the hole and electron pockets composing the Fermi surface are of the same size.

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“…It has been reported that the Weyl nodes can occur at points other than high symmetry k-path unlike nodal line semimetals. 18,20 Type I Weyl points cause point-like Fermi surface (FS) and hence difficult to identify. However, 2D band structure of tilted Dirac cone causes the crossed Fermi lines (see Fig.1(g)) centred at Weyl node.…”

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confidence: 99%

Coexistence of spin semimetal and Weyl semimetal behavior in FeRhCrGe

et al. 2019

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In this letter, we report the discovery of a new class of spintronic materials, namely spin semimetals (SSM), employing both theoretical and experimental tools. The band structure of this class of materials is such that one of the spin bands resembles that of a semi-metal, while the other is similar to that of an insulator/semiconductor. This report is the experimental verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a magnetic moment 3 µB and a Curie temperature of 550 K. The measurement below 300 K shows nearly temperature independent conductivity and a relatively moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous first principles calculations. Band structure calculations also reveal that the spin up (semi metallic) band has combined features of type II Weyl and nodal line semimetal. As such, this study opens up the possibility of a new class of material with combined spintronic and topological properties, which is important both from fundamental and applied point of view.PACS numbers: 75.47.Np, 75.76.+j, 76.80.+y Introduction: Recent developments in magnetic Heusler alloys, such as the discovery of half metallic ferromagnets (HMF) have fuelled the area of spintronics research considerably. 1-5 One of the spin bands is metallic while the other is either semiconducting or insulating in this class of materials. Later, spin gapless semiconductors (SGS) 6 were discovered which gained prominence over the half metals due to their unique properties. Magnetic semiconductors 7 with unequal band gaps constitute another class of spintronic materials that produce high spin polarized charge carriers at elevated temperatures. Fully compensated ferrimagnet 8 is another unique class. In this letter, we discovered a new interesting class of materials, which we term as spin semi-metals (SSM). One of the main motives of this paper is to highlight the discovery of SSM and its importance and applications in the field of spintronics. We demonstrate the existence of necessary features of SSM in a realistic material, FeR-hCrGe. Furthermore, the spin up band of this material is also found to acquire a combined feature of type II Weyl 9,10 and nodal line 11,12 semi-metal.

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Symmetry demanded topological nodal-line materials

Cited by 204 publications

References 168 publications

Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH3

Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH3

Chemical Principles of Topological Semimetals

Coexistence of spin semimetal and Weyl semimetal behavior in FeRhCrGe

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