Probing Quantum Hall Pseudospin Ferromagnet by Resistively Detected NMR

TL;DR

This study uses resistively detected NMR to explore quantum Hall pseudospin ferromagnetic states, revealing differences in spin excitations at various Landau level crossing points in a two-subband electron system.

Contribution

It demonstrates the application of RD-NMR to detect and analyze QHPF states and their spin excitations, highlighting an unexpected absence of signal at certain crossing points.

Findings

RD-NMR detects easy-axis QHPF state around ν=4.

Enhanced RD-NMR signal and relaxation rate near LL crossing points.

Unexpected missing signal at one LL crossing point.

Abstract

Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to investigate a two-subband electron system in a regime where quantum Hall pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals that the easy-axis QHPF state around the total filling factor $\nu =4 $ can be detected by the RD-NMR measurement. Approaching one of the Landau level (LL) crossing points, the RD-NMR signal strength and the nuclear spin relaxation rate $1/T_{1}$ enhance significantly, a signature of low energy spin excitations. However, the RD-NMR signal at another identical LL crossing point is surprisingly missing which presents a puzzle.