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 $H_c$, a reentrance appears as a peak in the temperature dependent resistivity $ρ_{xx}(T)$ at $T$ = $T_p$, similar to that observed in graphite where it was attributed to local superconductivity. The $T_p(H)$ relationship follows a power-law dependence $T_p\sim(H-H_c)^{1/v}$ where $v$ can be derived from the temperature dependence of the zero-field resistivity $ρ_0(T) \sim T^v$. From concurrent measurements of the transverse $ρ_{xx}(T)$ and Hall $ρ_{xy}(T)$ magnetoresistivities, we reveal a clear correlation between the rapidly increasing $ρ_{xy}(T)$ and the occurrence of a peak in the $ρ_{xx}(T)$ curve. Quantitative analysis indicates that the reentrant metallic behavior arises from the competition of the magneto conductivity $σ_{xx}(T)$ with an additional component $Δσ_{xx}(T)=κ_Hσ_{xx}(T)$ where $κ_H=[ρ_{xy}(T)/ρ_{xx}(T)]^2$ is the Hall factor. We find that the Hall factor ($κ_H \approx 0.4$) at peak temperature $T_p$ is nearly field-independent, leading to the observed $T_p(H)$ relationship. Furthermore, the reentrant metallic behavior in $ρ_{xx}(T)$ also is reflected in the behavior of $ρ_{xx}(H)$ that ranges from non-saturating at $T>70$ K to saturation at liquid helium temperatures. The latter can be explained with the magnetic field dependence of the Hall factor $κ_H(H)$. Our studies demonstrate that a semiclassical theory can account for the 'anomalies' in the magnetotransport phenomena of NbP without invoking an exotic mechanism.