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 (T ). 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 [Formula: see text] GPa and [Formula: see text] 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 T 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.

Revealing the anisotropy effects on the critical magnetic field in CaC6 superconductor

“…where λ αβ denotes the electron-phonon coupling con- stant, which is defined in the matrix form as follows [24]: (4) The Eliashberg equations (1) and (2) are numerically solved by using the modified numerical procedures initially developed for the isotropic materials [25][26][27][28][29] and later adopted to three-band CaC 6 superconductor [12]. In this context, the input parameters for the calculations are the critical temperature T C = 11.5 K and the corresponding elements of the Coulomb pseudopotential (µ ⋆ αβ ) matrix [24]: 4) and (5) are arranged with respect to the assumed band indices.…”

Strong-Coupling Character of Superconducting Phase in Heavily-Doped cg-C4H4

“…The Eliashberg equations have been solved for 2201 Matsubara frequencies (M = 1100) by using the method presented in [10,11] and recently tested in [12]. In the considered case, the obtained Eliashberg solutions are stable for T ≥ 20 K.…”

Characterization of the superconducting phase in tellurium hydride at high pressure

“…Specifically, the Eliashberg formalism is employed in the isotopic form within the Migdal approximation [16], in correspondence to the isotropic approximation of pairing gap proposed in [10]. Herein, the Eliashberg equations are solved on the imaginary axis, and later analytically continued on the real axis, by using the numerical methods employed previously in [17][18][19][20][21]. The following form of the Eliashberg equations on the imaginary axis (i ≡ √ −1) is adopted during calculations:…”