Dispersive line shape in the vicinity of the {\nu} = 1 quantum Hall state: Coexistence of Knight shifted and unshifted resistively detected NMR responses

TL;DR

This paper investigates the dispersive line shape in resistively detected NMR near the ν=1 quantum Hall state, revealing coexistence of shifted and unshifted responses linked to local phase formation and hyperfine interactions.

Contribution

It provides the first detailed analysis of the dispersive NMR line shape near ν=1, showing the coexistence of Knight shifted and unshifted signals and their relation to local phase formation.

Findings

Splitting increases near ν=1 and is proportional to hyperfine coupling.

Peak frequency shifts linearly with magnetic field, matching substrate signals.

Nuclear spin relaxation time T1 is extremely long at the peak frequency.

Abstract

The frequency splitting between the dip and the peak of the resistively detected nuclear magnetic resonance (RDNMR) dispersive line shape (DLS) has been measured in the quantum Hall effect regime as a function of filling factor, carrier density and nuclear isotope. The splitting increases as the filling factor tends to {\nu} = 1 and is proportional to the hyperfine coupling, similar to the usual Knight shift versus {\nu}-dependence. The peak frequency shifts linearly with magnetic field throughout the studied filling factor range and matches the unshifted substrate signal, detected by classical NMR. Thus, the evolution of the splitting is entirely due to the changing Knight shift of the dip feature. The nuclear spin relaxation time, T1, is extremely long (hours) at precisely the peak frequency. These results are consistent with the local formation of a {\nu} = 2 phase due to the existence of spin singlet D$^-$ complexes.