Reentrant metallic behavior in the Weyl semimetal NbP

We report the occurrence of reentrant metallic behavior in the Weyl semimetal NbP. When the applied magnetic field H is above a critical value Hc, a reentrance appears as a peak in the temperature-dependent resistivity ρxx(T) at T=Tp, similar to that observed in graphite where it was attributed to local superconductivity. The Tp(H) relationship follows a power-law dependence Tp∼(H-Hc)1/ν where ν can be derived from the temperature dependence of the zero-field resistivity ρ0(T)∼Tν. From concurrent measurements of the transverse ρxx(T) and Hall ρxy(T) magnetoresistivities, we reveal a clear correlation between the rapidly increasing ρxy(T) and the occurrence of a peak in the ρxx(T) curve. Quantitative analysis indicates that the reentrant metallic behavior arises from the competition of the magnetoconductivity σxx(T) with an additional component Δσxx(T)=κHσxx(T) where κH=[ρxy(T)/ρxx(T)]2 is the Hall factor. We find that the Hall factor (κH≈0.4) at peak temperature Tp is nearly field independent, leading to the observed Tp(H) relationship. Furthermore, the reentrant metallic behavior in ρxx(T) also is reflected in the behavior of ρxx(H) that ranges from nonsaturating at T>70K to saturation at liquid-helium temperatures. The latter can be explained with the magnetic field dependence of the Hall factor κH(H). Our paper demonstrates that a semiclassical theory can account for the "anomalies" in the magnetotransport phenomena of NbP without invoking an exotic mechanism.