C—代数A中的L_(A)—紧元及其特性

在本文中,我们引入了C^(n)—代数A中“L_(A)—紧元”的概念,刻画了L_(A)—紧元的特性.其中定理2.4包含了文献[1]中命题2.12.12及文献[2]中性质2.3.13.

The C-G coefficients for the space group D_6~1h

In this paper, the eigenfunction method established by Chen Jin-quan is used to compute the C-G coefficients in regard to the coupling between symmetry points and lines in the first Brillouin zone of the structure D6h^1, space group. Therewith, the wave vector selection rule and the C-G series, are also given as the middle result of computing the C-G coefficients.

Quantum Groups by Ore Extensions Associated withGroup Algebras

As a continuation of the work of Beattie on quantum groups constructed byOre extensions, in this paper, we characterize their centre and discuss the category ofquantum Yang-Baxter modules over them. In addition, we determine all finite dimen-sional irreducible representations over these quantum groups.

Unconventional materials:the mismatch between electronic charge centers and atomic positions

The complete band representations(BRs)have been constructed in the work of topological quantum chemistry.Each BR is expressed by either a localized orbital at a Wyckoff site in real space,or by a set of irreducible representations in momentum space.In this work,we define unconventional materials with a common feature of the mismatch between average electronic centers and atomic positions.They can be effectively diagnosed as whose occupied bands can be expressed as a sum of elementary BRs(eBRs),but not a sum of atomic-orbital-induced BRs(aBRs).The existence of an essential BR at an empty site is described by nonzero real-space invariants(RSIs).The"valence"states can be derived by the aBR decomposition,and unconventional materials are supposed to have an uncompensated total"valence"state.The high-throughput screening for unconventional materials has been performed through the first-principles calculations.We have discovered 423 unconventional compounds,including thermoelectronic materials,higher-order topological insulators,electrides,hydrogen storage materials,hydrogen evolution reaction electrocatalysts,electrodes,and superconductors.The diversity of these interesting properties and applications would be widely studied in the future.

On tempered and square integrable representations of classical p-adic groups

This paper has two aims. The first is to give a description of irreducible tempered representations of classical p-adic groups which follows naturMly the classification of irreducible square integrable representations modulo cuspidal data obtained by Mceglin and the author of this article （2002）. The second aim of the paper is to give a description of an invariant （partially defined function） of irreducible square integrable representation of a classical p-adic group （defined by Mceglin using embeddings） in terms of subquotients of Jacquet modules. As an application, we describe behavior of partially defined function in one construction of square integrable representations of a bigger group from such representations of a smaller group （which is related to deformation of Jordan blocks of representations）.

High-throughput screening for Weyl semimetals with S_(4) symmetry

Based on irreducible representations(or symmetry eigenvalues) and compatibility relations(CR), a material can be predicted to be a topological/trivial insulator(satisfying CR) or a topological semimetal(violating CR). However, Weyl semimetals(WSMs) usually go beyond this symmetry-based strategy. In other words, Weyl nodes could emerge in a material, no matter if its occupied bands satisfy CR, or if the symmetry indicators are zero. In this work, we propose a new topological invariant v for the systems with S4 symmetry(i.e., the improper rotation S_(4)(≡IC_(4z)) is a proper fourfold rotation(C_(4z)) followed by inversion(I)), which can be used to diagnose the WSM phase. Moreover, v can be easily computed through the onedimensional Wilson-loop technique. By applying this method to the high-throughput screening in our first-principles calculations, we predict a lot of WSMs in both nonmagnetic and magnetic compounds.Various interesting properties(e.g., magnetic frustration effects, superconductivity and spin-glass order,etc.) are found in predicted WSMs, which provide realistic platforms for future experimental study of the interplay between Weyl fermions and other exotic states.

Quantification of Symmetry

Symmetry is conventionally described in a polarized manner that the system is either completely symmetric or completely asymmetric.Using group theoretical approach to overcome this dichotomous problem,we introduce the degree of symmetry(DoS) as a non-negative continuous number ranging from zero to unity.Do S is defined through an average of the fidelity deviations of Hamiltonian or quantum state over its transformation group G,and thus is computable by making use of the completeness relations of the irreducible representations of G.The monotonicity of Do S can effectively probe the extended group for accidental degeneracy while its multi-valued natures characterize some(spontaneous) symmetry breaking.