Observation of Dirac-like energy band and ring-torus Fermi surface associated with the nodal line in topological insulator CaAgAs

Takane, Daichi; Nakayama, K.; Souma, S.; Wada, Taichi; Okamoto, Yoshio; Takenaka, Koshi; Yamakawa, Youichi; Yamakage, Ai; Mitsuhashi, T.; Horiba, Koji; Kumigashira, Hiroshi; Takahashi, Takashi; Sato, Takafumi

doi:10.1038/s41535-017-0074-z

Cited by 115 publications

(50 citation statements)

References 63 publications

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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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Section: Weyl Semimetalsmentioning

confidence: 99%

Chemical Principles of Topological Semimetals

2018

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“…A line node of this kind constitutes an accidental band crossing and does not require a partner as in the case of Z 2 monopole charge line nodes. Various materials in this class of topological semimetal have been theoretically identified, including the experimentally confirmed materials, such as CaAgP (145,146,147) and PbTaSe 2 (148,149,150,147) families of materials.…”

Section: Mirror-and Glide Mirror-symmetry Protected Nodal Line Semimementioning

confidence: 99%

Topological Semimetals from First Principles

Gao

Venderbos

Kim

et al. 2019

Annu. Rev. Mater. Res.

215

118

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We review recent theoretical progress in the understanding and prediction of novel topological semimetals. Topological semimetals define a class of gapless electronic phases exhibiting topologically stable crossings of energy bands. Different types of topological semimetals can be distinguished based on the degeneracy of the band crossings, their codimension (e.g. point or line nodes), as well as the crystal space group symmetries on which the protection of stable band crossings relies. The dispersion near the band crossing is a further discriminating characteristic. These properties give rise to a wide range of distinct semimetal phases such as Dirac or Weyl semimetals, point or line node semimetals, and type-I or type-II semimetals. In this review we give a general description of various families of topological semimetals with an emphasis on proposed material realizations from first-principles calculations. The conceptual framework for studying topological gapless electronic phases is reviewed, with a particular focus on the symmetry requirements of energy band crossings, and the relation between the different families of topological semimetals is elucidated. In addition to the paradigmatic Dirac and Weyl semimetals, we pay particular attention to more recent examples of topological semimetals, which include nodal line semimetals, multifold fermion semimetals, triple-point semimetals. Less emphasis is placed on their surface state properties, responses to external probes, and recent experimental developments. 1 arXiv:1810.08186v1 [cond-mat.mes-hall]

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“…[65][66][67] Now they are extensively studied in semimetals. 68 The type of Lifshitz transitions governed by the conservation of the topological charge N 2 is shown in Fig. 17 on example of bilayer graphene, when one graphene layer is shifted with respect to the other one.…”

Section: Lifshitz Transition Governed By Conservation Of N2 Chargementioning

confidence: 99%