Transmission of radio-frequency waves and nuclear magnetic resonance in lanthanum superhydrides

TL;DR

This study demonstrates how $^1$H NMR measurements can be performed in diamond anvil cells to investigate high-temperature superconductivity in lanthanum hydrides at pressures up to 165 GPa, revealing superconducting transitions around 260-267 K.

Contribution

It introduces a method for conducting $^1$H NMR in diamond anvil cells to study superconductivity in lanthanum hydrides at ultra-high pressures, enabling new insights into their properties.

Findings

Superconducting transition observed at ~260-267 K in LaH$_{12}$.

Pronounced suppression of $^1$H NMR signal below $T_c$.

Estimated superconducting gap between 427 and 671 K.

Abstract

The discovery of near-room temperature superconductivity in the lanthanum hydride LaH$_{10}$ has revolutionized this field of research. However, the need to use diamond anvils for the synthesis of such superconductors severely limits the number of experimental techniques to study these materials. Nuclear magnetic resonance (NMR) is one of the key methods for probing spin systems of superconductors. In this work, we show how $^1$H NMR measurements can be realized in diamond anvil cells to study high-temperature superconductivity in lanthanum polyhydrides at pressures up to 165 GPa. In the newly discovered superhydride LaH$_{12}$, we observed a pronounced suppression of the $^1$H NMR signal intensity below $\textit{T$_{c}$(onset)}$ = 260 K in a magnetic field of 7 T, corresponding to the screening of the radio-frequency pulses. Below the critical temperature of superconductivity, all $^1$H NMR characteristics, including the spin-lattice relaxation rate $\textit{1/T$_{1}$T}$, demonstrate pronounced features, evidencing the bulk nature of the superconducting transition. In zero field, the radio-frequency signal transmission through the LaH$_{12}$ sample shows a pronounced drop below $\textit{T$_{c}$(onset)}$ = 267 K, confirming the superconducting nature of the transition. A description of the $\textit{1/T$_{1}$T}$ data with an exponential form allows the estimation of the superconducting gap $\textit{${\Delta}$(0)}$ lying between 427 and 671 K (corresponding to 36.8 to 57.8 meV), and the ratio $\textit{R$_{\Delta}$ = 2${\Delta}$(0)/k$_B$T$_c$}$ between 3.76 and 5.16 in the synthesized hydride sample.