Special Issue "Recent Advances in Novel Topological Materials"

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

Deadline for manuscript submissions: closed (31 May 2019).

Special Issue Editors

Guest Editor
Dr. Guang Bian

University of Missouri-Columbia, Department of Physics and Astronomy, Columbia, United States
Website | E-Mail
Interests: topological insulators; 2D materials; MBE; ARPES
Guest Editor
Dr. Tay-Rong Chang

Department of Physics, National Cheng Kung University, Taiwan
Website | E-Mail
Interests: topological materials; multiferroics; iridate; TMDC

Special Issue Information

Dear Colleagues,

Ever since the experimental discovery of the first 2D and 3D topological insulators, there have been intense emerging worldwide research activities in searching for and identifying new topological phases of condensed matter. Recent years have witnessed the laboratory-based realization of numerous novel topological materials, such as topological crystalline insulator, Weyl semimetals and new fermion matters. The interest in this topic arises from, not only the realization of exotic theoretical concepts in fundamental physics, but also the promise of device applications, which can potentially revolutionize the entire Si-based electronics industry.

This Special Issue on “Recent Advances in Novel Topological Materials” is intended to provide a unique and timely forum aimed at covering a broad description of novel topological matters. Scientists working in this fast-developing field are invited to contribute to this cause.

The topics summarized under the keywords broadly cover examples of the great number of sub-topics in mind. The volume is especially open for any innovative contributions involving theoretical prediction, crystal growth and experimental characterizations of new topological materials.

Dr. Guang Bian
Dr. Tay-Rong Chang
Guest Editors

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 1400 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 insulators/semimetals
  • Topological superconductors
  • Sample growth and characterizations
  • Theoretical prediction and analysis

Published Papers (6 papers)

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Research

Open AccessArticle
Bi2Te3 Topological Insulator for Domain-Wall Dark Pulse Generation from Thulium-Doped Fiber Laser
Crystals 2019, 9(7), 337; https://doi.org/10.3390/cryst9070337
Received: 31 May 2019 / Revised: 23 June 2019 / Accepted: 28 June 2019 / Published: 29 June 2019
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Abstract
We have experimentally demonstrated domain-wall (DW) dark pulses from a thulium-doped fiber laser incorporating a topological insulator saturable absorber (SA). The bulk-structured Bi2Te3 was used as the SA, which was constructed on a fiber ferrule platform through the deposition of [...] Read more.
We have experimentally demonstrated domain-wall (DW) dark pulses from a thulium-doped fiber laser incorporating a topological insulator saturable absorber (SA). The bulk-structured Bi2Te3 was used as the SA, which was constructed on a fiber ferrule platform through the deposition of the Bi2Te3 mixed with distilled water. The DW dark pulses were generated from the thulium-doped fiber laser cavity with a dual wavelength at 1956 nm and 1958 nm. The dark pulse width and the repetition rate were measured as ~10.3 ns and ~20.7 MHz over the pump power of ~80 mW, respectively. To the best of our knowledge, this work is the first demonstrated generation of the DW dark pulse from a thulium-doped fiber laser using nanomaterial-based SA. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Ferroelectric Self-Poling in GeTe Films and Crystals
Crystals 2019, 9(7), 335; https://doi.org/10.3390/cryst9070335
Received: 30 May 2019 / Revised: 21 June 2019 / Accepted: 24 June 2019 / Published: 28 June 2019
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Abstract
Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for [...] Read more.
Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Topological Phase Transition in a One-Dimensional Elastic String System
Crystals 2019, 9(6), 313; https://doi.org/10.3390/cryst9060313
Received: 20 May 2019 / Revised: 13 June 2019 / Accepted: 15 June 2019 / Published: 18 June 2019
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Abstract
We show that topological interface mode can emerge in a one-dimensional elastic string system which consists of two periodic strings with different band topologies. To verify their topological features, Zak-phase of each band is calculated and reveals the condition of topological phase transition [...] Read more.
We show that topological interface mode can emerge in a one-dimensional elastic string system which consists of two periodic strings with different band topologies. To verify their topological features, Zak-phase of each band is calculated and reveals the condition of topological phase transition accordingly. Apart from that, the transmittance spectrum illustrates that topological interface mode arises when two topologically distinct structures are connected. The vibration profile further exhibits the non-trivial interface mode in the domain wall between two periodic string composites. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Transformation of the Topological Phase and the Edge Modes of Double-Bilayer Bismuthene with Inter-Bilayer Spacing
Crystals 2019, 9(5), 266; https://doi.org/10.3390/cryst9050266
Received: 4 April 2019 / Revised: 18 May 2019 / Accepted: 20 May 2019 / Published: 22 May 2019
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Abstract
The transformations of the topological phase and the edge modes of a double-bilayer bismuthene were investigated with first-principles calculations and Green’s function as the inter-bilayer spacing increased from 0 Å to 10 Å. At a critical spacing of 2 Å, a topological phase [...] Read more.
The transformations of the topological phase and the edge modes of a double-bilayer bismuthene were investigated with first-principles calculations and Green’s function as the inter-bilayer spacing increased from 0 Å to 10 Å. At a critical spacing of 2 Å, a topological phase transition from a topological insulator to a band insulator resulting from a band inversion between the highest valence band and the second lowest conduction band, was observed, and this was understood based on the particular orbital characters of the band inversion involved states. The edge modes of double-bilayer bismuthene survived the phase transition. When d was 2 Å < d < 4 Å, the interaction between the edge modes of two separated bismuthene bilayers induced an anti-crossing gap and resulted in a trivial band connection. At and beyond 4 Å, the two bilayers behavior decoupled entirely. The results demonstrate the transformability of the topological phase and the edge modes with the inter-bilayer spacing in double-bilayer bismuthene, which may be useful for spintronic applications. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Reconfigurable Topological Phases in Two-Dimensional Dielectric Photonic Crystals
Crystals 2019, 9(4), 221; https://doi.org/10.3390/cryst9040221
Received: 1 March 2019 / Revised: 17 April 2019 / Accepted: 19 April 2019 / Published: 24 April 2019
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Abstract
The extensive research on photonic topological insulators has opened up an intriguing way to control electromagnetic (EM) waves. In this work, we numerically demonstrate reconfigurable microwave photon analogues of topological insulator (TIs) in a triangular lattice of elliptical cylinders, according to the theory [...] Read more.
The extensive research on photonic topological insulators has opened up an intriguing way to control electromagnetic (EM) waves. In this work, we numerically demonstrate reconfigurable microwave photon analogues of topological insulator (TIs) in a triangular lattice of elliptical cylinders, according to the theory of topological defects. Multiple topological transitions between the trivial and nontrivial photonic phases can be realized by inhomogeneously changing the ellipse orientation, without altering the lattice structure. Topological protection of the edge states and reconfigurable topological one-way propagation at microwave frequencies, are further verified. Our approach provides a new route towards freely steering light propagations in dielectric photonic crystals (PCs), which has potential applications in the areas of topological signal processing and sensing. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Photonic Topological States in a Two-Dimensional Gyrotropic Photonic Crystal
Crystals 2019, 9(3), 137; https://doi.org/10.3390/cryst9030137
Received: 6 February 2019 / Revised: 1 March 2019 / Accepted: 2 March 2019 / Published: 7 March 2019
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Abstract
Time-reversal symmetry (TRS) of electrons is associated with an anti-unitary operator with T2=1, which induces Kramers degeneracy and plays an important role in realizing the quantum spin Hall effect (QSHE). By contrast, TRS of photons is described by [...] Read more.
Time-reversal symmetry (TRS) of electrons is associated with an anti-unitary operator with T 2 = 1 , which induces Kramers degeneracy and plays an important role in realizing the quantum spin Hall effect (QSHE). By contrast, TRS of photons is described by T b 2 = 1 . We point out that due to this difference, TRS is not the necessary condition for the construction of the photonic analogue of the QSHE. Instead, by constructing an artificial pseudo TRS T p with T p 2 = 1 in a photonic system, one can realize the photonic Kramers degeneracy and a pair of topological protected edge states, a photonic analogue of the QSHE. Specifically, by retrieving the optical parameters of materials with the pseudo TRS, we propose a photonic topological insulator (PTI) utilizing a pair of double-degenerate transverse electric (TE) and transverse magnetic (TM) polarizations to mimic the spin up and down states of the electron. We demonstrate that the unidirectional polarization-dependent transportation of TE and TM edge states can be realized in this system based on computer simulations. For all possible symmetry types, we check the robustness of these topological states by using a complete set of impurities, including three Pauli matrices and one complex conjugate operator. The results show that the PTI is protected by the pseudo TRS T p . In general, an arbitrary pair of optical polarizations on the Bloch sphere can be utilized to construct photonic pseudospin states and the PTI. Our findings confirm the physical meaning of the pseudo TRS and may provide guidance for future PTI designs. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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