Effect of van Hove singularity on the isotope effect and critical temperature of H${}_3$S hydride superconductor as a function of pressure

Abstract

We have performed density functional calculations in conjunction with the linearized Migdal-Eliashberg equations and the functional derivative approach, which takes into account the energy-range dependence of the density of states at the Fermi level ($N(\epsilon )$ variable on the scale of phonon energy), to determine the evolution of the critical temperature ($T_c$) and the isotope effect coefficient ($\alpha$) of H${}_3$S as a function of pressure on its $lm\bar{3}m$ crystal-structure range (from 162 to 250 GPa). Such approach, in comparison with $N(\epsilon )$=$N(0)$=const., improves the agreement of $T_c$ with available experiments on the whole range of studied pressure. Considering for $\alpha$ two main contributions: one positive coming from the electron-phonon (el-ph) and the other negative from the electron-electron interaction (el-el), we obtained a monotonic decrement as a function of pressure, independent of applied scheme ($N(\epsilon )$ or $N(0)$). However, when $N(\epsilon )$ is taken into account, an important renormalization occurs on both contributions, el-ph and el-el, improving the agreement with experimental data, specially for the high-pressure regime. The observed evolution of $T_c$ and $\alpha$ as a function of pressure indicates, thus, the crucial role of the energy-dependence on $N(\epsilon )$ for the proper analysis and description of the superconducting state on high-$T_c$ metal hydrides as H${}_3$S, by considering the role of its van Hove singularities.

12 pages, 12 figures

References in corpus (11)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Superconductive "sodalite"-like clathrate calcium hydride at high pressures
• Hydrogen sulphide at high pressure: a strongly-anharmonic phonon-mediated superconductor
• Cubic H${}_3$S around 200 GPa: an atomic hydrogen superconductor stabilized by sulfur
• First-principles study of the pressure and crystal-structure dependences of the superconducting transition temperature in compressed sulfur hydrides
• Nonstandard superconductivity or no superconductivity in hydrides under high pressure
• Electron-phonon coupling mechanisms for hydrogen-rich metals at high pressure
• Quantitative analysis of nonadiabatic effects in dense H${}_3$S and PH${}_3$ superconductors
• Comparison of pressurized sulfur hydride with conventional superconductors
• On the isotope effect in compressed superconducting H${}_{\text{3}}$S and D${}_{\text{3}}$S
• Spectroscopic signatures of phonons in high pressure superconducting hydrides