# Influence of magnetic and electric fields on universal conductance fluctuations in thin films of the Dirac semi-metal Cd3As2

## TL;DR

This study investigates how magnetic and electric fields influence universal conductance fluctuations in thin films of the Dirac semimetal Cd3As2, revealing symmetry-breaking effects and Fermi surface anisotropy through experimental and theoretical analysis.

## Contribution

It provides experimental evidence linking symmetry-breaking fields to conductance fluctuation changes in Dirac semimetals, supported by numerical calculations.

## Key findings

- Magnetic field beyond phase-breaking reduces fluctuations by sqrt(2).
- Gate voltage increases fluctuations due to Fermi surface anisotropy.
- Universal conductance fluctuations dominate intrinsic transport in Cd3As2.

## Abstract

Time-reversal invariance and inversion symmetry are responsible for the topological band structure in Dirac semimetals. These symmetries can be broken by applying an external magnetic or electric field, resulting in fundamental changes to the ground state Hamiltonian and a topological phase transition. We probe these changes via the magnetic-field dependence and gate voltage-dependence of universal conductance fluctuations in top-gated nanowires of the prototypical Dirac semimetal Cd3As2. As the magnetic field is increased beyond the phase-breaking field, we find a factor of sqrt(2) reduction in the magnitude of the universal conductance fluctuations, in agreement with numerical calculations that study the effect of broken time reversal symmetry in a 3D Dirac semimetal. In contrast, the magnitude of the fluctuations increases monotonically as the chemical potential is gated away from the charge neutrality point. This effect cannot be attributed to broken inversion symmetry, but can be explained by Fermi surface anisotropy. The concurrence between experimental data and theory in our study provides unequivocal evidence that universal conductance fluctuations are the dominant source of intrinsic transport fluctuations in mesoscopic Cd3As2 devices and offers a promising general methodology for probing the effects of broken symmetry in topological quantum materials.