Recently, Prof. ZHAO Jimin's group and the colleagues from the Institute of Physics of the Chinese Academy of Sciences, using the on-site in situ low-temperature variable-temperature ultrahigh-pressure ultrafast spectroscopy instrument, investigated the ultrafast dynamics of clathrate superhydride superconductor LaH_10±δ, and obtained the electron-phonon coupling (EPC) strength and superconducting energy gap of LaH_10±δ. This study was published in Nature Communications.

The recent development of on-site in situ high-pressure ultrafast spectroscopy technique has enabled the simultaneous acquisition of precise amplitudes and lifetimes in ultrafast relaxation, making it feasible to investigate superconducting correlated quantum materials. One important advancement is the capability of experimentally probing the EPC strength, superconducting energy gap, and phonon-bottleneck effect under high pressure conditions. 

Since the discovery of H₃S, the most prominent near-room temperature superconductors are clathrate superhydrides, whereby LaH_10±δ exhibits a T_c of 250-260 K under an ultrahigh pressure of 165-190 GPa. However, due to the small sample chamber of a diamond anvil cells, many experimental tools cannot be employed for detection, which makes it challenging to experimentally obtain key properties such as the EPC strength, microscopic superconducting pairing mechanism, and superconducting energy gap of hydrogen-rich superconductors. 

To date, direct experimental evidence for the strong EPC in high-T_c superhydride superconductors is still lacking. Meanwhile, the high-pressure ultrafast dynamics of various correlated quantum materials is often difficult to be carried out, leaving their non-equilibrium ultrafast dynamics unexplored.

In this study, Prof. ZHAO's group developed an on-site in situ low-temperature high-pressure ultrafast spectroscopy instrument, and used it to observe the ultrafast dynamics of LaH_10±δ at different temperatures. Researchers obtained ultrafast quasiparticle relaxation information on both the amplitude and lifetime, and detected the phonon-bottleneck effect near the superconducting transition temperature. 

Through the analysis of temperature-dependent and fluence-dependent experimental data, they obtained the EPC strength of LaH_10±δ as λ=2.58±0.11, the superconducting gap as Δ(0) =53±5meV, the gap ratio as 2Δ(0)/k_BT_c=5.6, and the gap parameter as ϑ=1.95. Besides, multiple direct experimental evidence obtained, especially the value of λ, all pointed to that strong EPC may be the cause of near-room-temperature superconductivity in clathrate superhydride compounds. 

The findings of this study advance the understanding of near-room-temperature superconducting mechanism, promote the development of the field of high-pressure ultrafast dynamics, and contribute to the understanding of the non-equilibrium ultrafast dynamics and phase transitions of numerous complex material systems under high pressure.