Negative c-axis longitudinal magnetoresistance in FeSe

Below the structural transition occurring at $T_s=90$\,K, FeSe exhibits positive transverse magnetoresistance when the current is applied parallel to the $ab$-plane. In this study, we show that, in contrast, when both the magnetic field and the current are aligned along the $c$-axis, the magnetotransport changes significantly. In this configuration, FeSe develops a sizable negative longitudinal magnetoresistance ($\sim$15\% at $T$=10\,K and $\mu_0H$=16\,T) in the nematic phase. We attribute this finding to the effect of the applied magnetic field on the scattering from spin fluctuations. Our observations reflect the intricate interplay between spin and orbital degrees of freedom in the nematic phase of FeSe.