Debye temperature in LaHx-LaDy superconductors

Abstract

The Debye temperature, T${}_{\theta }$=(h/2$\pi$)/k${}_B$$\omega$${}_{\theta }$, where the Debye frequency $\omega$${}_{\theta }$ is integrated characteristic frequency of full phonon spectrum, $\alpha$${}^2$($\omega$)F($\omega$). In the BCS theory, T${}_{\theta }$ in conjunction with electron-phonon coupling strength parameter, $\lambda$${}_{e-ph}$, determines the superconducting transition temperature, Tc. Despite a fact that more accurate theory of electron-phonon mediated superconductivity requires the knowledge of full phonon spectrum, $\alpha$${}^2$($\omega$)F($\omega$), which can be very accurately computed by first principles calculation technique, there is no experimental technique which can measure $\alpha$${}^2$($\omega$)F($\omega$) in highly-compressed near-room-temperature (NRT) superconductors. Thus, $\omega$${}_{\theta }$ remains to be the only measurable parameter of full phonon spectrum, $\alpha$${}^2$($\omega$)F($\omega$), which can be deduced by the fit of experimental temperature-dependent resistance data, R(T), to Bloch-Grüneisen equation. Taking in account that within electron-phonon mediated theory of superconductivity two isotopic counterparts (or, in case of NRT superconductors, the same superconducting phase at different pressures), designated by subscripts of 1 and 2, should be obey the relation of T${{}_{\theta }}_1$/T${{}_{\theta }}_2$=T${{}_c}_1$/T${{}_c}_2$, there is a way to reaffirm/disprove the electron-phonon mechanism of NRT superconductivity. In this paper, we perform the analysis for R3m-phase of H3S at different pressure, as well as for several superconductors in LaHx-LaDy system and show that there is a large disagreement between experimental data and T${{}_{\theta }}_1$/T${{}_{\theta }}_2$=T${{}_c}_1$/T${{}_c}_2$. Taking in account that similar disagreement has recently reported in H3S-D3S system, it can be concluded that primary origin for NRT superconductivity remains to be discovered.

20 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:2002.12859

References in corpus (14)

• Hydrogen sulphide at high pressure: a strongly-anharmonic phonon-mediated superconductor
• Pressure-induced decomposition of solid hydrogen sulfide
• Superconducting hydrides under pressure
• Superconducting Phase-Diagram of H3S under High Magnetic Fields
• Superconductivity up to 243 K in yttrium hydrides under high pressure
• Band-edge BCS-BEC crossover in a two-band superconductor: physical properties and detection parameters
• London penetration depth and thermal fluctuations in the sulphur hydride 203 K superconductor
• Classifying superconductivity in compressed H3S
• The road to room-temperature conventional superconductivity
• Pressure-induced Superconductivity in Tin Sulfide
• The role of thermal disorder for magnetism and the $\alpha -\gamma$ transition in Cerium; Results from density-functional theory
• Mechanism of High-Temperature Superconductivity in Correlated-Electron Systems
• Classifying superconductivity in ThH-ThD superhydrides/superdeuterides
• On the isotope effect in compressed superconducting H${}_{\text{3}}$S and D${}_{\text{3}}$S