Emergence of spin-active channels at a quantum Hall interface

TL;DR

This paper investigates the ground state phases at a quantum Hall interface between filling factors 4 and 3, revealing two distinct phases with different spin properties and the emergence of gapless spin excitations in one phase.

Contribution

It identifies and characterizes two phases at the quantum Hall interface, including a novel phase with gapless spin excitations beyond Hartree-Fock approximation.

Findings

Two distinct interface phases with different spin properties.

Emergence of gapless long-wavelength spin excitations in one phase.

Potential experimental detection via nuclear magnetic resonance.

Abstract

We study the ground state of a system with an interface between $\nu=4$ and $\nu=3$ in the quantum Hall regime. Far from the interface, for a range of interaction strengths, the $\nu=3$ region is fully polarized but $\nu=4$ region is locally a singlet. Upon varying the strength of the interactions and the width of the interface, the system chooses one of two distinct edge/interface phases. In phase A, stabilized for wide interfaces, spin is a good quantum number, and there are no gapless long-wavelength spin fluctuations. In phase B, stabilized for narrow interfaces, spin symmetry is spontaneously broken at the Hartree-Fock level. Going beyond Hartree-Fock, we argue that phase B is distinguished by the emergence of gapless long-wavelength spin excitations bound to the interface, which can, in principle, be detected by a measurement of the relaxation time $T_2$ in nuclear magnetic resonance.