NMR Study of Large Skyrmions in Al_{0.13}Ga_{0.87}As Quantum Wells

TL;DR

This study uses NMR to investigate large skyrmions in Al_{0.13}Ga_{0.87}As quantum wells near filling factor ν=1, revealing inhomogeneous spin polarization and supporting the presence of sizable skyrmionic excitations.

Contribution

It introduces a specialized NMR technique to distinguish signals in low polarization conditions and provides evidence for large skyrmions in these quantum wells.

Findings

Detected broad, negative spin polarization distribution in QWs

Observed thermally induced depolarization effects

Indications of large skyrmions from rapid T2^{-1} rates

Abstract

A nuclear magnetic resonance (NMR) study is reported of multiple (30) Al$_{0.13}$Ga$_{0.87}$As quantum well (QW) sample near the Landau level filling factor $\nu =1$. In these Al$_{0.13}$Ga$_{0.87}$As QWs the effective $g$ factor is nearly zero. This can lead to two effects: vanishing electronic polarization $(P)$ and skyrmionic excitations composed of a huge number of spins. As small $P$ values cause an overlap of the NMR signals from the QW and barriers, a special technique was employed to allow these two signals to be distinguished. The QW signal corresponds to a small, negative, and very broad distribution of spin polarization that exhibits thermally induced depolarization. Such a distribution can be attributed to sample inhomogeneities and/or to large skyrmions, the latter possibility being favored by observation of a very fast $T_{2}^{-1}$ rate.