Effect of paramagnetic impurities on superconductivity in polyhydrides: $\textit{s}$-wave order parameter in Nd-doped LaH$_{10}$

TL;DR

This study investigates how magnetic Nd impurities suppress superconductivity in LaH$_{10}$, revealing an isotropic s-wave pairing mechanism through magnetic field experiments and impurity effects.

Contribution

It provides the first detailed magnetic phase diagram of Nd-doped LaH$_{10}$ and demonstrates the impact of magnetic impurities on its superconducting properties.

Findings

Nd doping decreases T_C by 10-11 K per atom.

Superconductivity suppression correlates linearly with magnetic field and temperature.

Superhydrides exhibit isotropic s-wave pairing, consistent with electron-phonon interactions.

Abstract

Polyhydrides are a novel class of superconducting materials with extremely high critical parameters, which is very promising for applications. On the other hand, complete experimental study of the magnetic phase diagram for the best so far known superconductor, lanthanum decahydride LaH$_{10}$, encounters a serious complication because of the large upper critical magnetic field $\textit{H}$$_{C2}$(0), exceeding 120-160 T. Partial replacement of La atoms by magnetic Nd atoms results in a decrease of the upper critical field, which makes it attainable for existing pulse magnets. We found that addition of neodymium leads to significant suppression of superconductivity in LaH$_{10}$: each atomic % of Nd causes decrease in $\textit{T}$$_{C}$ by 10-11 K. Using strong pulsed magnetic fields up to 68 T, we constructed the magnetic phase diagram of the ternary (La,Nd)H$_{10}$ superhydride, which appears to be surprisingly linear with $\textit{H}$$_{C2}$ $\propto$ |$\textit{T}$ - $\textit{T}$$_C$|. The pronounced suppression of superconductivity in LaH$_{10}$ by magnetic Nd atoms and the robustness of $\textit{T}$$_C$ with respect to nonmagnetic impurities (e.g., Y, Al, C) under Anderson's theorem indicate the isotropic ($\textit{s}$-wave) character of conventional electron-phonon pairing in the synthesized superhydrides.