Negative magnetoresistance in Weyl semimetals NbAs and NbP： Intrinsic chiral anomaly and extrinsic effects

• Published in: Frontiers of physics Vol. 12; no. 3; pp. 19 - 28
• Main Authors: Li, Yupeng, Wang, Zhen, Li, Pengshan, Yang, Xiaojun, Shen, Zhixuan, Sheng, Feng, Li, Xiaodong, Lu, Yunhao, Zheng, Yi, Xu, Zhu-An
• Format: Journal Article
• Language: English
• Published: Beijing Higher Education Press 01.06.2017; Springer Nature B.V
• Subjects: Astronomy; Astrophysics and Cosmology; Atomic; chiral anomaly; Coherent scattering; Condensed Matter Physics; Electrons; extrinsic effects; Fermions; Graphene; Helicity; High temperature; Impurities; Localization; Magnetic fields; Magnetoresistance; Magnetoresistivity; Metalloids; Molecular; NBA; NBP; negative magnetoresistance; NMR; Nuclear magnetic resonance; Optical and Plasma Physics; Orbital scattering; Particle and Nuclear Physics; Phase coherence; Physics; Physics and Astronomy; Recent Progress on Weyl Semimetals; Review Article; Symmetry; Weyl semimetals; 半金属; 异常; 手性; 核磁共振; 自旋轨道; 负磁阻效应; Weyl semimetals; chiral anomaly; extrinsic effects; negative magnetoresistance
• ISSN: 2095-0462; 2095-0470
• DOI: 10.1007/s11467-016-0636-8

Chiral anomaly-induced negative magnetoresistance (NMR) has been widely used as critical transport evidence for the existence of Weyl fermions in topological semimetals. In this mini-review, we discuss the general observation of NMR phenomena in non-centrosymmetric NbP and NbAs. We show that NMR can arise from the intrinsic chiral anomaly of Weyl fermions and/or extrinsic effects, such as the superimposition of Hall signals; field-dependent inhomogeneous current flow in the bulk, i.e., current jetting; and weak localization (WL) of coexistent trivial carriers. The WL-controlled NMR is heavily dependent on sample quality and is characterized by a pronounced crossover from positive to negative MR growth at elevated temperatures, resulting from the competition between the phase coherence time and the spin-orbital scattering constant of the bulk trivial pockets. Thus, the correlation between the NMR and the chiral anomaly need to be scrutinized without the support of complimentary techniques. Because of the lifting of spin degeneracy, the spin orientations of Weyl fermions are either parallel or antiparallel to the momentum, which is a unique physical property known as helicity. The conservation of helicity provides strong protection for the transport of Weyl fermions, which can only be effectively scattered by magnetic impurities. Chemical doping with magnetic and non-magnetic impurities is thus more convincing than the NMR method for detecting the existence of Weyl fermions.