Electron-hole compensation effect between topologically trivial electrons and nontrivial holes in NbAs

Fermi surface topology and negative longitudinal magnetoresistance observed in centrosymmetric NbAs2 semimetal

We report transverse and longitudinal magneto-transport properties of NbAs2 single crystals. Attributing to the electron-hole compensation, non-saturating large transverse magnetoresistance reaches up to 8000 at 9 T at 1.8 K with mobility around 1 to 2 m^2V^-1S^-1. We present a thorough study of angular-dependent Shubnikov-de Haas (SdH) quantum oscillations of NbAs2. Three distinct oscillation frequencies are identified. First-principles calculations reveal four types of Fermi pockets: electron alpha pocket, hole beta pocket, hole gamma pocket and small electron delta pocket. Although the angu…

Weyl nodes close to the Fermi energy in NbAs

The noncentrosymmetric transition metal monopnictides NbP, TaP, NbAs and TaAs are a family of Weyl semimetals in which pairs of protected linear crossings of spin-resolved bands occur. These so-called Weyl nodes are characterized by integer topological charges of opposite sign associated with singular points of Berry curvature in momentum space. In such a system anomalous magnetoelectric responses are predicted, which should only occur if the crossing points are close to the Fermi level and enclosed by Fermi surface pockets penetrated by an integer flux of Berry curvature, dubbed Weyl pockets.…

Extremely large magnetoresistance in topologically trivial semimetal $α$-WP$_2$

Extremely large magnetoresistance (XMR) was recently discovered in many non-magnetic materials, while its underlying mechanism remains poorly understood due to the complex electronic structure of these materials. Here, we report an investigation of the $α$-phase WP$_2$, a topologically trivial semimetal with monoclinic crystal structure (C2/m), which contrasts to the recently discovered robust type-II Weyl semimetal phase in $β$-WP$_2$. We found that $α$-WP$_2$ exhibits almost all the characteristics of XMR materials: the near-quadratic field dependence of MR, a field-induced up-turn in resist…

通过双极效应增强半Heusler拓扑材料的横向和纵向磁热电功率

Transverse and Longitudinal Magnetothermopower Promoted by Ambipolar Effect in Half-Heusler Topological Materials

半Heusler拓扑材料DyPtBi通过双极效应实现大横向和纵向磁热电功率，突破传统权衡，展示高有效热电性能。

Extremely large magnetoresistance and compensated Fermi surfaces in the antiferromagnetic semimetal YbAs

A number of rare-earth monopnictides have topologically non-trivial band structures together with magnetism and strong electronic correlations. In order to examine whether the antiferromagnetic (AFM) semimetal YbAs ($T\rm_N$ = 0.5 K) exhibits such a scenario, we have grown high-quality single crystals using a flux method, and characterized the magnetic properties and electronic structure using specific heat, magnetotransport and angle-resolved photoemission spectroscopy (ARPES) measurements, together with density functional theory (DFT) calculations. Both ARPES and DFT calculations find no evi…

周期Weyl半金属超结构的轴子不稳定性

Axionic Instability of Periodic Weyl-Semimetal Superstructures

本研究揭示Weyl半金属超结构中费米面嵌套与库仑相互作用可驱动自发手性对称破缺，形成无平移对称破缺的动力学轴子绝缘体态，并在磁性掺杂Bi₂Se₃中提出轴子凝聚稳定磁化螺旋序的实现方案。