Nuclear-spin relaxation of $^{207}$Pb in ferroelectric powders

TL;DR

This study investigates the nuclear-spin relaxation times of $^{207}$Pb in ferroelectric powders and crystals across a temperature range, revealing dominant relaxation mechanisms and implications for Schiff-moment experiments.

Contribution

First comprehensive temperature-dependent nuclear-spin relaxation analysis of $^{207}$Pb in ferroelectric materials relevant for Schiff-moment searches.

Findings

Transverse relaxation time T2 ≈ 1.5 ms across all samples.

Longitudinal relaxation time T1 varies from over an hour at low temperatures to about 7 seconds at room temperature.

Relaxation mechanisms transition from two-phonon Raman at high T to single-phonon processes at low T.

Abstract

Motivated by a recent proposal by O. P. Sushkov and co-workers to search for a P,T-violating Schiff moment of the $^{207}$Pb nucleus in a ferroelectric solid, we have carried out a high-field nuclear magnetic resonance study of the longitudinal and transverse spin relaxation of the lead nuclei from room temperature down to 10 K for powder samples of lead titanate (PT), lead zirconium titanate (PZT), and a PT monocrystal. For all powder samples and independently of temperature, transverse relaxation times were found to be $T_2\approx 1.5 $ms, while the longitudinal relaxation times exhibited a temperature dependence, with $T_1$ of over an hour at the lowest temperatures, decreasing to $T_1\approx 7 $s at room temperature. At high temperatures, the observed behavior is consistent with a two-phonon Raman process, while in the low temperature limit, the relaxation appears to be dominated by a single-phonon (direct) process involving magnetic impurities. This is the first study of temperature-dependent nuclear-spin relaxation in PT and PZT ferroelectrics at such low temperatures. We discuss the implications of the results for the Schiff-moment search.