Spin in fractional quantum Hall systems

TL;DR

This paper investigates spin polarization transitions in fractional quantum Hall systems at filling factor 2/3, revealing a potential low-energy half-polarized state and analyzing its implications for quantum Hall ferromagnetism.

Contribution

It introduces a detailed analysis of spin states at 2/3 filling, highlighting a possible new ground state and comparing fractional and integer quantum Hall systems.

Findings

Discovery of a low excited half-polarized state near the transition

Comparison of fractional and integer quantum Hall states

Insights into the stability of spin configurations with inhomogeneities

Abstract

A system at filling factor 2/3 could be a candidate for a quantum Hall ferromagnet at integer filling factor of composite fermions. Using exact diagonalization with electrons on a torus we study the transition from the singlet ground state to the polarized ground state at this filling and look for signatures of quantum Hall ferromagnetism. Differences between the fractional and corresponding integer systems are emphasised. Most interestingly, we find around the transition a low excited half-polarized state which might become the ground state in the thermodynamical limit. We study its structure and compare it to the singlet and polarized ground states. A new interpretation of the singlet state is suggested and comparison of the filling factors 2/3 and 2/5 is presented. Adding magnetic inhomogeneities into the system we investigate the stability of all the three involved states and the tendency to build up domains like in conventional ferromagnets.