Multi-photon resonances in pure multiple-pulse NQR

TL;DR

This paper reports the observation and theoretical analysis of multi-photon resonances in a spin 3/2 system under multiple pulse RF sequences and low-frequency fields, revealing insights into slow atomic motion in solids.

Contribution

It introduces a novel excitation scheme for measuring effective RF fields and provides a comprehensive theoretical description using both rotating frame and Floquet theory.

Findings

Resonance lines decrease slowly with mode number

Theoretical models agree with experimental data

Multi-frequency spectra probe slow atomic motion

Abstract

We have observed multi-photon resonances in a system with a spin 3/2 irradiated simultaneously by a multiple pulse radiofrequency sequence and a low frequency field swept in the range 0-80 kHz. The used excitation scheme allowed us to measure the effective field of the radiofrequency sequence. A peculiarity of this scheme is that the intensity of the resonance lines decreases slowly with the mode number. The theoretical description of the effect is presented using both the rotating frame approximation and the Floquet theory. Both approaches give indentical results at the calculation of the resonance frequencies, transition probabilities and shifts of resonance frequency. The calculated magnetization vs. the frequency of the low-frequency field agrees well with the obtained experimental data. The multi-frequency spectra give a way for studying slow atomic motion in solids.