Resistively Detected NMR in Quantum Hall States: Investigation of the anomalous lineshape near $\nu=1$

TL;DR

This paper investigates the unusual lineshape observed in resistively detected NMR near filling factor =1 in a 2D electron gas, revealing that the lineshape can be inverted by applying a DC current, indicating multiple underlying mechanisms.

Contribution

It demonstrates that the anomalous NMR lineshape near =1 can be controlled and inverted by external current, suggesting distinct mechanisms behind the resistance minima and maxima.

Findings

Anomalous dispersive lineshape observed near =1.

Lineshape inversion achieved by applying DC current.

Distinct mechanisms inferred for minima and maxima in lineshape.

Abstract

A study of the resistively detected nuclear magnetic resonance (RDNMR) lineshape in the vicinity of $\nu=1$ was performed on a high-mobility 2D electron gas formed in GaAs/AlGaAs. In higher Landau levels, application of an RF field at the nuclear magnetic resonance frequency coincides with an observed minimum in the longitudinal resistance, as predicted by the simple hyperfine interaction picture. Near $\nu=1$ however, an anomalous dispersive lineshape is observed where a resistance peak follows the usual minimum. In an effort to understand the origin of this anomalous peak we have studied the resonance under various RF and sample conditions. Interestingly, we show that the lineshape can be completely inverted by simply applying a DC current. We interpret this as evidence that the minima and maxima in the lineshape originate from two distinct mechanisms.