Topological crystalline insulators define a new class of topological insulator phases with gapless surface states protected by crystalline symmetries. In this work, we present a general theory to classify topological crystalline insulator phases based on the representation theory of space groups. Our approach is to directly identify possible nontrivial surface states in a semi-infinite system with a specific surface, of which the symmetry property can be described by 17 two-dimensional space groups. We reproduce the existing results of topological crystalline insulators, such as mirror Chern insulators in the pm or pmm groups, Cnv topological insulators in the p4m, p31m and p6m groups, and topological nonsymmorphic crystalline insulators in the pg and pmg groups. Aside from these existing results, we also obtain the following new results: (1) there are two integer mirror Chern numbers (Z 2 ) in the pm group but only one (Z) in the cm or p3m1 group for both the spinless and spinful cases; (2) for the pmm (cmm) groups, there is no topological classification in the spinless case but Z 4 (Z 2 ) classifications in the spinful case; (3) we show how topological crystalline insulator phase in the pg group is related to that in the pm group; (4) we identify topological classification of the p4m, p31m, and p6m for the spinful case; (5) we find topological non-symmorphic crystalline insulators also existing in pgg and p4g groups, which exhibit new features compared to those in pg and pmg groups. We emphasize the importance of the irreducible representations for the states at some specific high-symmetry momenta in the classification of topological crystalline phases. Our theory can serve as a guide for the search of topological crystalline insulator phases in realistic materials.
Two-dimensional Dirac physics has aroused great interests in condensed matter physics ever since the discovery of graphene and topological insulators. The ability to control the properties of Dirac cones, such as bandgap and Fermi velocity, is essential for various new phenomena and the next-generation electronic devices. On the basis of first-principles calculations and an analytical effective model, we propose a new Dirac system with eight Dirac cones in thin films of the (LaO) 2 (SbSe 2 ) 2 family of materials, which has the advantage in its tunability: the existence of gapless Dirac cones, their positions, Fermi velocities and anisotropy all can be controlled by an experimentally feasible electric field. We identify layer-dependent spin texture induced by spin-orbit coupling as the underlying physical reason for electrical tunability of this system. Furthermore, the electrically tunable quantum anomalous Hall effect with a high Chern number can be realized by introducing magnetization into this system.
In this paper, we present a compact surface-potential-based drain current model in molybdenum disulfide (MoS2) field-effect transistors (FETs). Considering variable range hopping (VRH) transport via band-tail states in MoS2 transistors, an explicit solution for surface potential has been derived and it provides a good description over different regions of operation by comparisons with numerical data. Based on the charge-sheet model (CSM), which applies to drift-diffusion transport, the current expression including contact resistance and velocity saturation effect is developed. Furthermore, the presented model is validated and shows a good agreement with the experimental data for MoS2 FETs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.