Dipolar broadening of nuclear spin resonance under dynamical pumping

TL;DR

This paper investigates how nuclear spin resonance lines shift and narrow with increasing nuclear polarization under dynamical pumping, providing a method to measure polarization and a theoretical model linking decay rates to resonance width.

Contribution

It introduces a combinatorial approach to analyze polarization-dependent nuclear spin resonance and provides an explicit solution connecting decay rates to resonance line width.

Findings

Resonance center shifts linearly with polarization.

Resonance width decreases from maximum to zero as polarization increases.

Line shape can serve as a measure of nuclear polarization.

Abstract

We study the polarisation dependence of the homogeneously broadened nuclear spin resonance in a crystal. We employ a combinatorial method to restrict the nuclear states to a fixed polarisation and show that the centre of the resonance is shifted linearly with the nuclear polarisation by up to the zero polarisation line width. The width shrinks from its maximum value at zero polarisation to zero at full polarisation. This suggests to use the line shape as a direct measure of nuclear polarisation reached under dynamical pumping. In the limit of single quantum of excitation above the fully ferromagnetic state, we provide an explicit solution to the problem of nuclear spin dynamics which links a bound on the fastest decay rate to the observable width of the resonance line.