# Hidden Anisotropy in the Drude Conductivity of Charge Carriers with Dirac-Schr\"odinger Dynamics

## TL;DR

This paper reveals that in a two-dimensional electron gas with mixed Dirac and Schr"odinger characteristics, intrinsic anisotropy in conductivity can arise despite isotropic Fermi surfaces, controllable by Fermi energy or temperature.

## Contribution

It introduces a model showing how scalar disorder leads to anisotropic transport in carriers with Dirac-Schr"odinger dynamics, a novel insight into anisotropic conductivity mechanisms.

## Key findings

- Anisotropic conductivity emerges despite isotropic Fermi surface.
- Tuning Fermi energy or temperature controls anisotropy.
- Exact Boltzmann solution reveals hidden control parameters.

## Abstract

We show that the conductivity of a two-dimensional electron gas can be intrinsically anisotropic despite isotropic Fermi surface, energy dispersion, and disorder configuration. In the model we study, the anisotropy stems from the interplay between Dirac and Schr\"odinger features combined in a special two-band Hamiltonian describing the quasiparticles similar to the low-energy excitations in phosphorene. As a result, even scalar isotropic disorder scattering alters the nature of the carriers and results in anisotropic transport. Solving the Boltzmann equation exactly for such carriers with point-like random impurities we find a hidden knob to control the anisotropy just by tuning either the Fermi energy or temperature. Our results are expected to be generally applicable beyond the model studied here, and should stimulate further search for the alternative ways to control electron transport in advanced materials.