Transmission of Radio‐Frequency Waves and Nuclear Magnetic Resonance in Lanthanum Superhydrides

Abstract The discovery of near‐room‐temperature superconductivity in the lanthanum hydride LaH 10 has revolutionized this research field. However, the need to use diamond anvils for the synthesis of hydride superconductors severely limits the experimental techniques to study these materials. Nuclear magnetic resonance (NMR) is one of the key methods for probing spin systems of superconductors. Here we show how 1 H NMR can be realized in diamond anvil cells to study 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 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, all 1 H NMR characteristics, including the nuclear spin‐lattice relaxation rate 1/ T 1 T , exhibit pronounced features that may be associated with superconductivity. In zero field, the radio‐frequency signal transmission shows a pronounced drop below T c onset ≈ 267‒279 K, indicating the very beginning of the transition in the most ideal microcrystals. A description of the 1/ T 1 T data with an exponential form allows the estimation of the superconducting gap Δ(0) = 427‒671 K (corresponding to 36.8‒57.8 meV), and the ratio R Δ = 2Δ (0) / k B T c between 3.76 and 5.16 in the synthesized polyhydride.