Coexistence of orbital and quantum critical magnetoresistance in FeSe1-x Sx

The recent discovery of a nonmagnetic nematic quantum critical point (QCP) in the iron chalcogenide family FeSe1-xSx has raised the prospect of investigating, in isolation, the role of nematicity on the electronic properties of correlated metals. Here we report a detailed study of the normal state transverse magnetoresistance (MR) in FeSe1-xSx for a series of S concentrations spanning the nematic QCP. For all temperatures and x values studied, the MR can be decomposed into two distinct components: one that varies quadratically in magnetic field strength μ0H and one that follows precisely the quadrature scaling form recently reported in metals at or close to a QCP and characterized by a H-linear MR over an extended field range. The two components evolve systematically with both temperature and S substitution in a manner that is determined by their proximity to the nematic QCP. This study thus reveals the coexistence of two independent charge sectors in a quantum critical system. Moreover, the quantum critical component of the MR is found to be less sensitive to disorder than the quadratic (orbital) MR, suggesting that detection of the latter in previous MR studies of metals near a QCP may have been obscured.