Optical properties of superconducting pressurized LaH10

Abstract

Recently superconductivity has been discovered at around 200 K in a hydrogen sulfide system and around 260 K in a lanthanum hydride system, both under pressures of about 200 GPa. These record-breaking transition temperatures bring within reach the long-term goal of obtaining room temperature superconductivity. We have used first-principle calculations based on density functional theory (DFT) along with Migdal-Eliashberg theory to investigate the electron-phonon mechanism for superconductivity in the F m3m phase proposed for the LaH10 superconductor. We show that the very high transition temperature Tc results from a highly optimized electron-phonon interaction that favors coupling to high frequency hydrogen phonons. Various superconducting properties are calculated, such as the energy gap, the isotope effect, the specific heat jump at Tc, the thermodynamic critical field and the temperature-dependent penetration depth. However, our main emphasis is on the finite frequency optical properties, measurement of which may allow for an independent determination of Tc and also a confirmation of the mechanism for superconductivity.

Anomalous behavior in high-pressure carbonaceous sulfur hydride

“…, where 𝑟 = 3.52 in the weak coupling (BCS) limit, but is likely higher in this case, since in other high-pressure hydrides there is evidence for strong coupling. In particular, for both H3S and LaH10, the electron-phonon coupling constant is estimated to be [11] ~2 and 𝑟 is 4.5-4.8 for pressures around 200 GPa [11][12][13]. Also, based on the reported 𝑅(𝑇, 𝐻) curves for C-S-H, Talantsev has estimated the electron-phonon coupling constant to be ~2 as well [14].…”

Infrared imaging of samples in ultra high pressure diamond anvil cells

“…Further details of these and similar calculations for reflectance properties of pressurized hydrides can be found in Refs. 5,6,8,9 . The upper frame shows the absolute reflectance for several temperatures ranging from T = 0.1T c to T c , where T c is the superconducting critical temperature.…”

Spectral properties and enhanced superconductivity in renormalized Migdal-Eliashberg theory

“…ME theory is commonly used to phenomenologically describe properties of the normal and superconducting states arising from el-ph interactions across many different materials. ME theory has been successfully applied to understand the superconducting transition temperature in LaH 10 under high pressure 8,9 , reproduce the single-particle tunneling density of states in lead 10 , and provide theoretical support in the analysis of electronic band renormalizations seen in angle-resolved photo-emission (ARPES) experiments in strongly correlated systems such as the cuprates 11 . In some applications, self-consistent ME solutions are needed as in the case of reproducing replica bands arising from a forward scattering electron-phonon interaction at the interface of monolayer FeSe on an SrTiO 3 substrate or graphene/h-BN heterostructures 12,13 , and reproducing the phonon peak positions arising from multi-phonon scattering processes observed in high-resolution electron-tunneling spectroscopy on Nb-doped SrTiO 3 14 .…”