Anomalous Hall effect in anisotropic type-II Weyl semimetals

TL;DR

This paper analyzes the anomalous Hall effect in overtilted (type-II) Weyl semimetals, extending previous work to include the coexistence of electron and hole pockets and considering anisotropy and tilt effects.

Contribution

It provides a nonperturbative calculation of the CPT-odd electromagnetic response in type-II Weyl semimetals, incorporating lattice effects and regularization, with application to WTe₂.

Findings

The Hall response remains finite across the Lifshitz transition.

Fermi-sea and Fermi-surface contributions partially cancel, affecting the Hall conductivity.

The Hall response is strongly anisotropic and depends on tilt and anisotropy parameters.

Abstract

We extend our previous analysis [Phys. Rev. D 109, 065005 (2024)] of CPT-odd electromagnetic response in tilted, anisotropic Weyl semimetals to the overtilted (type-II) regime, where electron and hole pockets coexist at the Fermi level. Starting from the minimal QED sector of the Standard-Model Extension matched to a lattice-motivated anisotropic Dirac Hamiltonian with tilt, we compute the zero-temperature finite-density effective action nonperturbatively from the vacuum polarization tensor, and corroborate the result using a complementary chiral kinetic theory formulation that consistently incorporates both Fermi-sea and Fermi-surface contributions. In the type-II regime the unbounded linear dispersion necessitates a physical ultraviolet regularization. Implementing a hard momentum cutoff tied to the lattice bandwidth, we show that the CPT-odd, axion-like response remains finite across the type-I to type-II Lifshitz transition, while acquiring tilt- and anisotropy-dependent renormalizations together with nonuniversal, cutoff-sensitive terms governed by the geometry of the electron and hole pockets. As a concrete application, we evaluate the anomalous Hall conductivity in the prototypical type-II Weyl semimetal WTe$_2$, using parameters extracted from first-principles calculations and experiments, and find that Fermi-sea and Fermi-surface contributions are comparable and partially cancel, yielding a finite and strongly anisotropic Hall response characteristic of the overtilted regime.