Magnetoresistance- a blunt tool in the study of correlated electron systems.

We examine magnetoresistance data from a variety of so-called “strange metals”, along with the predictions of numerical models, some of considerable sophistication. The latter invoke a variety of effects, including quasiparticle scattering rates and/or effective masses that vary during magnetic-field-induced Fermi-surface orbits, or complex three-dimensional spatial variations in charge-density and/or scattering. A majority of the experimental data and model results are indistinguishable from the predictions of a simple analytical model that contains few adjustable parameters. Moreover, in the low- and high-field limits, this analytical model proves identical to an empirical “universal” relationship that has been widely used to explore “strange metal” magnetoresistance data. These comparisons demonstrate that it is very difficult to use magnetoresistance to distinguish effects due to spatial non-uniformity (i.e., disorder) from those caused by time-dependent variations of quasiparticle properties (e.g., effective mass, scattering rate) (or anything else). We conclude by assessing circumstances under which magnetoresistance might yield useful information.