Inducing a metal-insulator transition in disordered interacting Dirac fermion systems via an external magnetic field

TL;DR

This study uses quantum Monte Carlo simulations to explore how magnetic fields, disorder, and interactions induce metal-insulator transitions in two-dimensional Dirac fermion systems, revealing complex localization mechanisms.

Contribution

It demonstrates how magnetic fields combined with interactions and disorder lead to diverse insulating phases in Dirac fermion systems, highlighting the nuanced interplay affecting transport properties.

Findings

Magnetic fields reduce the critical Zeeman field for band-insulation due to spin-polarization.

Magnetic fields promote localization, leading to Mott or Anderson insulators at moderate field strengths.

Insulating phases occur without full electron spin polarization.

Abstract

We investigate metal-insulator transitions on an interacting two-dimensional Dirac fermion system using the determinant quantum Monte Carlo method. The interplay between Coulomb repulsion, disorder and magnetic fields, drives the otherwise semi-metallic regime to insulating phases exhibiting different characters. In particular, with the focus on the transport mechanisms, we uncover that their combination exhibits dichotomic effects. On the one hand, the critical Zeeman field $B_c$, responsible for triggering the band-insulating phase due to spin-polarization on the carriers, is largely reduced by the presence of the electronic interaction and quenched disorder. On the other hand, the insertion of a magnetic field induces a more effective localization of the fermions, facilitating the onset of Mott or Anderson insulating phases. Yet these occur at moderate values of $B$, and cannot be explained by the full spin-polarization of the electrons.