Transition-metal dipnictide PtBi2 exhibits rich structural and physical properties with topological semimetallic behavior and extremely large magnetoresistance (XMR) at low temperatures. We have investigated the electrical and magnetic properties of trigonal-phase PtBi2-x single crystals with x ~ 0.4. Profound de Haas–van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillations are observed. Through fast Fourier transformation (FFT) analyses, four oscillation frequencies are extracted, which result from α, β, γ, and δ bands. By constructing the Landau fan diagram for each band, the Berry phase is extracted demonstrating the non-trivial nature of the α, β, and δ bands. Despite Bi deficiency, we observe the Zeeman splitting in dHvA and SdH oscillations under moderate magnetic field and the moderate Landé g factor (4.97–6.48) for the α band. Quantitative analysis of the non-monotonic field dependence including the sign change of the Hall resistivity suggests that electrons and holes in our system are not perfectly compensated thus not responsible for the XMR effect.
PdSb 2 is a candidate for hosting 6-fold-degenerate exotic fermions (beyond Dirac and Weyl fermions). The nontrivial band crossing protected by the non-symmorphic symmetry plays a crucial role in physical properties. We have for the first time grown high-quality single crystals of PdSb 2 and characterized their physical properties under several stimuli (temperature, magnetic field, and pressure). While it is a diamagnetic Fermi-liquid metal under ambient pressure, PdSb 2 exhibits a large magnetoresistance with continuous increase up to 14 T, which follows the Kohler's scaling law at all temperatures. This implies one-band electrical transport, although multiple bands are predicted by first principles calculations. By applying magnetic field along the [111] direction, de Haas-van Alphen oscillations are observed with frequency of 102 T. The effective mass is nearly zero (0.045m 0 ) with the Berry phase close to , confirming that the band close to the R point has a nontrivial character. Under quasi-hydrostatic pressure (p), evidence for superconductivity is observed in the resistivity below the critical temperature T c . The domeshaped T c versus p is obtained with maximum ~2.9 K. We argue that the formation of Cooper pairs (bosons) is the consequence of the redistribution of the 6-fold-degenerate fermions under pressure.
Among one-dimensional transition-metal trichalcogenides, TaSe3 is unconventional in many respects. One is its strong topological semimetallicity as predicted by first-principles calculations. We report the experimental investigations of the electronic properties of one-dimensional-like TaSe3 single crystals. While the b-axis electrical resistivity shows good metallicity with a high residual resistivity ratio greater than 100, an extremely large magnetoresistance is observed reaching ≈7 × 103% at 1.9 K for 14 T. Interestingly, the magnetoresistance follows the Kohler’s rule with nearly quadratic magnetic field dependence, consistent with the electron–hole compensation scenario as confirmed by our Hall conductivity data. Both the longitudinal and Hall conductivities show Shubnikov-de Haas oscillations with two frequencies: Fα ≈ 97 T and Fβ ≈ 186 T. Quantitative analysis indicates that Fα results from the two-dimensional-like electron band with the non-trivial Berry phase [1.1π], and Fβ from the hole band with the trivial Berry phase [0(3D) − 0.16π(2D)]. Our experimental findings are consistent with the predictions based on first-principles calculations.
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