Nontrivial topological states in the tantalum dipnictides TaX2 (X = As, P)

Abstract

The intriguing quasiparticles in solids, known as Dirac, Weyl, and Majorana fermions, etc. with properties akin to those theoretically predicted but never realized in high-energy physics, have excited intensive research activities in recent years. The transition metal dipnictides are attractive because of their extremely large magnetoresistance that is usually attributed to the carrier compensation effect. We briefly review herein the crystal growth, magneto-transport measurements, and theoretical studies of tantalum dipnictides TaAs 2 and TaP 2 , with the emphasis being put on discussion of the nontrivial topological states in both materials. The analysis of quantum oscillations of the magnetoresistance unveils nonzero Berry phase. The chiral negative longitudinal magnetoresistance further points to possible Weyl state, which was recently theoretically suggested as the result of the magnetic field-induced Zeeman splitting effect no matter how large the field is. The analysis of these intriguing behaviors could brush up our understanding about the family of materials and would be valuable for future work on investigating the magnetic field-induced topological phase transition in such semimetals.

A new transition metal diphosphide α-MoP2 synthesized by a high-temperature and high-pressure technique

“…Transition metal diphosphides (TmP 2 , Tm = transition metal) represent an important family with rich physical properties that have received renewed research interest owing to the nontrivial topological states associated with exotic properties such as extremely large magnetoresistance (XMR). [1][2][3][4][5][6] These fundamentally important and technically useful physical properties naturally suggest the exploration of analogue compounds; this led to the discovery of the OsGe 2 -type structure of TmP 2 . [7][8][9] Since such nonmagnetic TmP 2 generally show XMR, for example in ZrP 2 , α-and β -WP 2 , β -MoP 2 , TaP 2 , etc., due to either the non-trivial topological electronic states or compensated carriers, [3][4][5][6] OsGe 2 -type MoP 2 is naturally expected to have similar intriguing physical properties.…”

Superconductivity in PtPb$_{4}$ with Possible Nontrivial Band Topology

“…Following the advent of topological insulators (TIs), the search for topological quantum materials with diverse symmetry-enforced topological states, characterized by the nontrivial topological invariants, has attracted a flurry of research interest in both condensedmatter physics and materials science [1,2]. For instance, both three dimensional Dirac semimetals (DSMs) with fourfold degenerate band crossings and Weyl semimetals (WSMs) with pairs of Weyl nodes due to the broken inversion symmetry or time-reversal symmetry, have been demonstrated to exhibit extraordinary physical properties, such as extremely large magnetoresistance, ultrahigh carrier mobility, and chiral anomaly induced negative magnetoresistance [3][4][5][6][7][8][9][10][11][12][13][14]. Another prominent example is the topological nodal-line semimetals (NLSMs) in which Dirac bands cross along a one-dimensional trajectory (line or loop) in momentum space, in contrast to the isolated Dirac nodes in TIs and DSMs.…”