Special Issue "Advances in Topological Materials"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: 31 December 2020.

Special Issue Editor

Dr. Artem Pronin
Website
Guest Editor
Physikalisches Institut, Universität Stuttgart Pfaffenwaldring 57, 70569 Stuttgart, Germany
Interests: Topological effects in condensed matter; 3D Dirac and Weyl physics; Strongly correlated electron systems, Superconductivity, Multiferroics, ferroelectrics; dielectric relaxation; Metal-insulator transitions; Low-energy electrodynamics of condensed matter

Special Issue Information

Dear Colleagues,

It is my pleasure to announce this Special Issue of Crystals on topological materials. Graphene is probably the greatest inspiration in current solid-state research. Many unique pro­per­ties of graphene are due to its peculiar electronic structure, characterized by the linear electronic band disper­sion and the crossings of these bands near the Fermi level. This band structure leads to a charge motion that is described by the Dirac Hamiltonian for massless particles, rather than by the standard Schrödinger Hamiltonian. The search for other materials, where similar physics would be observed, has led to the theoretical predictions and experimental discovery of topological insulators as well as Dirac and Weyl semimetals. In topological insulators, the surface states provide con­duc­tion (while the bulk is insulating) and the electronic structure of these states is similar to the electronic structure of graphene. The Dirac cones in topological insulators are symmetry-protected and thus robust against perturbations. Dirac and Weyl semimetals, in turn, possess linearly dispersing bands in their bulk with the band crossing points being protected either by symmetry or topology. The family of different topological elec­tronic phases in solids continues to grow: the theoretical predictions of nodal-line, triple-point, and type-II Weyl semimetals have recently been ac­companied by different experimental verifications for these novel phases. Common to all these states is the electronic low-energy band structure, which is represented by crossing linear bands. Research on these novel phases and on related quantum phenomena, provides strong ties between solid-state and high-energy physics. On the other hand, the excitement surrounding topological materials is also fueled by appealing potential applications. Topological semimetals are known for their high mobility and large magnetoresistance that can be exploited in high-speed electronics and spintronics. Valley degrees of freedom also open up possibilities for valleytronics applica­tions. Electronic superlenses made from topological semimetals have been suggested to collimate electrons beyond diffraction limits in scanning tunneling microscopes. The robust sur­face states of such compounds can be utilized in surface-related chemical processes, such as catalysis. The fundamental interest and application potential are both calling for thoughtful theoretical and experimental investigations on topological materials. In this Special Issue, we welcome contributions from both theorists and experimentalists on all relevant aspects of this novel field.

Dr. Artem Pronin
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Topological effects in condensed matter
  • Weyl and Dirac semimetals
  • Topological insulators
  • Skyrmions and real-space topology
  • Topological chiral crystals

Published Papers (2 papers)

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Research

Open AccessArticle
Ideal Photonic Weyl Nodes Stabilized by Screw Rotation Symmetry in Space Group 19
Crystals 2020, 10(7), 605; https://doi.org/10.3390/cryst10070605 (registering DOI) - 12 Jul 2020
Abstract
Topological photonics have developed in recent years since the seminal discoveries of topological insulators in condensed matter physics for electrons. Among the numerous studies, photonic Weyl nodes have been studied very recently due to their intriguing surface Fermi arcs, Chiral zero modes and [...] Read more.
Topological photonics have developed in recent years since the seminal discoveries of topological insulators in condensed matter physics for electrons. Among the numerous studies, photonic Weyl nodes have been studied very recently due to their intriguing surface Fermi arcs, Chiral zero modes and scattering properties. In this article, we propose a new design of an ideal photonic Weyl node metacrystal, meaning no excessive states are present at the Weyl nodes’ frequency. The Weyl node is stabilized by the screw rotation symmetry of space group 19. Group theory analysis is utilized to reveal how the Weyl nodes are spawned from line nodes in a higher symmetry metacrystal of space group 61. The minimum four Weyl nodes’ complex for time reversal invariant systems is found, which is a realistic photonic Weyl node metacrystal design compatible with standard printed circuit board techniques and is a complement to the few existing ideal photonic Weyl node designs and could be further utilized in studies of Weyl physics, for instance, Chiral zero modes and scatterings. Full article
(This article belongs to the Special Issue Advances in Topological Materials)
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Open AccessArticle
Infrared Optical Conductivity of Bulk Bi2Te2Se
Crystals 2020, 10(7), 553; https://doi.org/10.3390/cryst10070553 - 28 Jun 2020
Abstract
Mid- and near-infrared measurements reveal that the optical conductivity of the three-dimensional topological insulator, Bi2Te2Se, is dominated by bulk carriers and shows a linear-in-frequency increase at 0.5 to 0.8 eV. This linearity might be interpreted as a signature of [...] Read more.
Mid- and near-infrared measurements reveal that the optical conductivity of the three-dimensional topological insulator, Bi2Te2Se, is dominated by bulk carriers and shows a linear-in-frequency increase at 0.5 to 0.8 eV. This linearity might be interpreted as a signature of three-dimensional (bulk) Dirac bands; however, band-structure calculations show that transitions between bands with complex dispersion contribute instead to the inter-band optical conductivity at these frequencies and, hence, the observed linearity is accidental. These results warn against the oversimplified interpretations of optical-conductivity measurements in different Dirac materials. Full article
(This article belongs to the Special Issue Advances in Topological Materials)
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