Abstract
Magnetoresistance has a history of revealing key electronic characteristics of materials. From early measurements on noble metals to definitive characterization of localization effects in semiconductors to recent studies of topological materials, the magnetoresistive response provides an experimental technique to explore the Fermi surface in detail, and to predict and craft physical properties through its sign, functional form, and potential quantum character. Linear magnetoresistance in density-wave systems has eluded clear explanation for over half a century. Here, we present measurements that lead to a general explanation based on unusual current paths tied to the formation of long-range charge or spin order. This mechanism potentially extends to the large magnetoresistance observed in semimetals like Bi, graphite, and WTe2.
The magnetoresistance (MR) of a material is typically insensitive to reversing the applied field direction and varies quadratically with magnetic field in the low-field limit. Quantum effects, unusual topological band structures, and inhomogeneities that lead to wandering current paths can induce a cross-over from quadratic to linear MR with increasing magnetic field. Here we explore a series of metallic charge- and spin-density-wave systems that exhibit extremely large positive linear MR. By contrast to other linear MR mechanisms, this effect remains robust down to miniscule magnetic fields of tens of Oersted at low temperature. We frame an explanation of this phenomenon in a semiclassical narrative for a broad category of materials with partially gapped Fermi surfaces due to density waves.
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