Supercell symmetry modified spectral statistics of Kramers-Weyl fermions

TL;DR

This paper investigates the spectral statistics of Kramers-Weyl fermions in a chaotic quantum dot, revealing how supercell symmetry influences the transition between different random matrix ensembles and affects conductance behavior.

Contribution

It identifies a supercell symmetry in the Kramers-Weyl Hamiltonian that explains the unexpected spectral statistics and their transition due to symmetry breaking.

Findings

Level spacing distribution follows orthogonal ensemble for small t

Supercell symmetry explains the spectral statistics behavior

Transition from weak localization to weak antilocalization observed

Abstract

We calculate the spectral statistics of the Kramers-Weyl Hamiltonian $H=v\sum_{\alpha} \sigma_\alpha\sin p_\alpha+t \sigma_0\sum_\alpha\cos p_\alpha$ in a chaotic quantum dot. The Hamiltonian has symplectic time-reversal symmetry ($H$ is invariant when spin $\sigma_\alpha$ and momentum $p_\alpha$ both change sign), and yet for small $t$ the level spacing distribution $P(s)\propto s^\beta$ follows the $\beta=1$ orthogonal ensemble instead of the $\beta=4$ symplectic ensemble. We identify a supercell symmetry of $H$ that explains this finding. The supercell symmetry is broken by the spin-independent hopping energy $\propto t\cos p$, which induces a transition from $\beta=1$ to $\beta=4$ statistics that shows up in the conductance as a transition from weak localization to weak antilocalization.