Topo-fermiology

TL;DR

This paper develops a symmetry-based framework to identify topological invariants in the phase offset of quantum oscillations in solids, revealing new insights into magnetotransport phenomena across various materials.

Contribution

It introduces a comprehensive symmetry classification for the phase offset in quantum oscillations, linking it to topological invariants and degeneracies in Landau levels.

Findings

Identifies symmetry classes where phase offset is a topological invariant.

Provides criteria for symmetry-enforced Landau level degeneracies.

Clarifies that a π phase offset is not exclusive to 3D Dirac metals.

Abstract

The modern semiclassical theory of a Bloch electron in a magnetic field now encompasses the orbital magnetic moment and the geometric phase. These two notions are encoded in the Bohr-Sommerfeld quantization condition as a phase ($\lambda$) that is subleading in powers of the field; $\lambda$ is measurable in the phase offset of the de Haas-van Alphen oscillation, as well as of fixed-bias oscillations of the differential conductance in tunneling spectroscopy. In some solids and for certain field orientations, $\lambda/\pi$ are robustly integer-valued owing to the symmetry of the extremal orbit, i.e., they are the topological invariants of magnetotransport. Our comprehensive symmetry analysis identifies solids in any (magnetic) space group for which $\lambda$ is a topological invariant, as well as identifies the symmetry-enforced degeneracy of Landau levels. The analysis is simplified by our formulation of ten (and only ten) symmetry classes for closed, Fermi-surface orbits. Case studies are discussed for graphene, transition metal dichalchogenides, 3D Weyl and Dirac metals, and crystalline and $\mathbb{Z}_2$ topological insulators. In particular, we point out that a $\pi$ phase offset in the fundamental oscillation should \emph{not} be viewed as a smoking gun for a 3D Dirac metal.