Observation of an in-plane magnetic-field-driven phase transition in a quantum Hall system with SU(4) symmetry

TL;DR

This paper reports the discovery of an in-plane magnetic-field-driven phase transition in a quantum Hall system with SU(4) symmetry, revealing a transition from SU(2) to SU(4) symmetry and suggesting a possible electron pairing state.

Contribution

It demonstrates a rapid collapse of SU(2) pseudospin ferromagnetic states into an SU(4) symmetric state induced by in-plane magnetic field in a two-subband GaAs/AlGaAs system.

Findings

Activation energy increases by up to 12 K within a narrow tilt angle range.

Observation of a phase transition from SU(2) to SU(4) symmetry.

Discussion of potential electron pairing with four-fold degeneracy.

Abstract

In condensed matter physics, the study of electronic states with SU(N) symmetry has attracted considerable and growing attention in recent years, as systems with such a symmetry can often have a spontaneous symmetry-breaking effect giving rise to a novel ground state. For example, pseudospin quantum Hall ferromagnet of broken SU(2) symmetry has been realized by bringing two Landau levels close to degeneracy in a bilayer quantum Hall system. In the past several years, the exploration of collective states in other multi-component quantum Hall systems has emerged. Here we show the conventional pseudospin quantum Hall ferromagnetic states with broken SU(2) symmetry collapsed rapidly into an unexpected state with broken SU(4) symmetry, by in-plane magnetic field in a two-subband GaAs/AlGaAs two-dimensional electron system at filling factor around $\nu=4$. Within a narrow tilting range angle of 0.5 degrees, the activation energy increases as much as 12 K. While the origin of this puzzling observation remains to be exploited, we discuss the possibility of a long-sought pairing state of electrons with a four-fold degeneracy.