Parallel magnetic field driven quantum phase transition in a thin topological insulator film

TL;DR

This paper demonstrates that a thin topological insulator film exhibits a magnetic field-driven quantum phase transition from an insulator to a semimetal when the top and bottom surface states are hybridized and the Fermi level is in the hybridization gap.

Contribution

It reveals a novel quantum phase transition induced by a parallel magnetic field in hybridized topological insulator thin films, which was previously thought to be unresponsive.

Findings

A nonzero diamagnetic response appears when surfaces are hybridized.

A quantum phase transition occurs at a finite parallel magnetic field.

Transition from insulator to semimetal with vanishing response.

Abstract

It is well-known that helical surface states of a three-dimensional topological insulator (TI) do not respond to a static in-plane magnetic field. Formally this occurs because the in-plane magnetic field appears as a vector potential in the Dirac Hamiltonian of the surface states and can thus be removed by a gauge transformation of the surface electron wavefunctions. Here we show that when the top and bottom surfaces of a thin film of TI are hybridized and the Fermi level is in the hybridization gap, a nonzero diamagnetic response appears. Moreover, a quantum phase transition occurs at a finite critical value of the parallel field from an insulator with a diamagnetic response to a semimetal with a vanishing response to the parallel field.