Oscillations of Echo Amplitude in Glasses in a Magnetic Field Induced by Nuclear Dipole-Dipole Interaction

TL;DR

This paper provides a theoretical analysis of how magnetic fields influence dipole echo amplitudes in glasses at very low temperatures, highlighting a universal behavior and matching experimental results without fitting parameters.

Contribution

The study introduces a universal analytic function describing dipole echo amplitude dependence on magnetic fields, valid when nuclear dipole-dipole energy is much smaller than Zeeman energy.

Findings

Nonmonotonic magnetic field dependence of echo amplitude

Universal analytic function describes the effect

Excellent agreement with experimental data

Abstract

The effect of a magnetic field on the dipole echo amplitude in glasses (at temperatures of about 10 mK) induced by the dipole-dipole interaction of nuclear spins has been theoretically studied. It has been shown that a change in the positions of nuclear spins as a result of tunneling and their interaction with the external magnetic field E_H lead to a nonmonotonic magnetic field dependence of the dipole echo amplitude. The approximation that the nuclear dipole-dipole interaction energy E_d is much smaller than the Zeeman energy E_H has been found to be valid in the experimentally important cases. It has been shown that the dipole echo amplitude in this approximation may be described by a simple universal analytic function independent of the microscopic structure of the two-level systems. An excellent agreement of the theory with the experimental data has been obtained without fitting parameters (except for the unknown echo amplitude)