Theory of anomalous magnetotransport from mass anisotropy

TL;DR

This paper develops a theoretical framework to understand how large anisotropic effective mass influences magnetotransport properties, including Hall effect and magnetoresistance, in underdoped cuprates and similar systems.

Contribution

It introduces a model showing how mass anisotropy can alter Hall effect sign and magnitude, and identifies a new B-linear magnetoresistance regime in anisotropic Fermi pockets.

Findings

Mass anisotropy can change the Hall effect's sign and magnitude.

A novel B-linear magnetoresistance regime is predicted.

Implications for high-field Hall measurements in cuprates are discussed.

Abstract

In underdoped YBa$_2$Cu$_3$O$_{6+x}$, there is evidence of a small Fermi surface pocket subject to substantial mass enhancement in the doping regime $ 0.12<p<0.16$. This mass enhancement may vary substantially over the Fermi surface, due to "hot spot" or other relevant physics. We therefore examine the magnetotransport of an electron-like Fermi pocket with large effective mass anisotropy. Within the relaxation time approximation, we show that even for a pocket with a fixed shape, the magnitude and sign of the Hall effect may change as the mass anisotropy changes (except at very large, likely inaccessible magnetic fields). We discuss implications for recent Hall measurements in near optimally doped cuprates in high fields. In addition we identify a novel intermediate asymptotic regime of magnetic field, characterized by B-linear magnetoresistance. Similar phenomena should occur in a variety of other experimental systems with anisotropic mass enhancement