Raman fingerprint of high-temperature superconductivity in compressed hydrides

TL;DR

This study demonstrates that Raman spectroscopy, combined with electrical measurements and theoretical modeling, provides a reliable, contact-free method to quantitatively analyze high-temperature superconductivity in compressed hydrides.

Contribution

It introduces high-quality Raman spectra of LaH10 under high pressure, confirming phonon-mediated superconductivity and enabling quantitative gap measurement, thus establishing Raman as a robust probe.

Findings

Raman spectra show phonon frequency and linewidth changes with temperature.

Electrical resistivity drops indicating superconductivity.

Theoretical modeling confirms phonon-mediated pairing mechanism.

Abstract

The discovery of high-temperature superconductivity in hydrogen-rich compounds under extreme pressures has prompted great excitement, intense research, but also debate over the past decade. Electrical transport has been the primary diagnostic tool for identifying superconductivity in these systems, whereas complementary probes, including magnetic, spectroscopic, tunnelling and ultrafast methods, remain mostly qualitative due to experimental constraints and sample heterogeneity. Recent concerns over their reliability have fuelled controversy, leading to scepticism and pointing out the need for alternative, quantitative approaches. In this study, we acquired unprecedented high-quality Raman spectra of hexagonal LaH10 at approximately 145 GPa and low temperatures, in conjunction with electrical transport measurements. Upon cooling, we observe a drop of resistivity and simultaneous remarkable variations of phonon frequencies and linewidths. These effects are interpreted and perfectly reproduced by the Migdal-Eliashberg theory, providing a definitive proof of phonon-mediated superconductivity and enabling a quantitative determination of the superconducting energy gap. Our results establish Raman spectroscopy as a robust, contact-free probe with micrometric resolution for studying high temperature superconductivity, opening a powerful route to its discovery and characterization.