On the critical temperature discontinuity at the theoretical bcc-fcc phase transition in compressed selenium and tellurium superconductors

Abstract

Recent hydrides-driven advent in the high-pressure phonon-mediated superconductivity motivates research on chemical elements which compound with hydrogen. It is desired that such elements should allow chemical pre-compression of hydrogen to assure the induction of the superconducting phase with the high transition temperature (TC). Herein, we present detailed theoretical insight into the properties of the superconducting state induced under pressure (p) in two of such component elements, namely selenium (Se) and tellurium (Te) at GPa and GPa, respectively. The assumed external pressure conditions allow us to conduct our analysis just above previously theoretically predicted bcc-fcc structural phase transition of Se and Te, and identify the possible associated discontinuity effect of the critical temperature. In particular, our numerical analysis is conducted within Migdal-Eliashberg formalism, due to the confirmed electron–phonon pairing mechanism and relatively high electron–phonon coupling constant in the materials of interest. We predict that TC values in Se and Te equal 8.13 K and 5.96 K, respectively, and mark the highest critical temperature values for these elements within the postulated fcc phase. Additionally, we supplement these results by the estimated maximum values of the superconducting energy band gap and the effective mass of electrons. We predict that all these parameters can be used as a guidelines for experimental observation of the critical temperature discontinuity and the corresponding bcc-fcc phase transition in Se and Te superconductors. Moreover, we show that the thermodynamics of superconducting phase in both elements may exhibit deviations from the conventional estimates of the Bardeen–Cooper–Schrieffer theory, and suggest existence of the strong-coupling and retardation effects. Finally, we note that our results can be also instructive for future screening of chemical elements for applications in superconducting hydrides.