ABSTRACT
New stable phase thorium decahydride Fm3Ì m-ThH10, a high-temperature superconductor with TC up to 241 K (-32 °C), critical field HC up to 71 T, and superconducting gap Δ0 of 52 meV at 80-100 GPa, is predicted by evolutionary algorithm USPEX. Another phase, P21/ c-ThH7, is found to be a superconductor with TC of 62 K. Analysis of the superconducting state was performed within Eliashberg formalism, and HC( T), Δ( T), and TC( P) functions with a jump in the specific heat at critical temperature were calculated. Several other new thorium hydrides were predicted to be stable under pressure, including ThH3, Th3H10, ThH4, and ThH6. Thorium (which has s2 d2 electronic configuration) forms high- TC polyhydrides similar to those formed by s2 d1 metals (Y-La-Ac). Thorium belongs to the Mg-Ca-Sc-Y-La-Ac family of elements forming high- TC superconducting hydrides.
ABSTRACT
The H5S2 and H2S compounds are the two candidates for the low-temperature phase of compressed sulfur-hydrogen system. We have shown that the value of Coulomb pseudopotential (µ*) for H5S2 ([TC]exp = 36 K and p = 112 GPa) is anomalously high. The numerical results give the limitation from below to µ* that is equal to 0.402 (µ* = 0.589), if we consider the first order vertex corrections to the electron-phonon interaction). Presented data mean that the properties of superconducting phase in the H5S2 compound can be understood within the classical framework of Eliashberg formalism only at the phenomenological level (µ* is the parameter of matching the theory to the experimental data). On the other hand, in the case of H2S it is not necessary to take high value of Coulomb pseudopotential to reproduce the experimental critical temperature relatively well (µ* = 0.15). In our opinion, H2S is mainly responsible for the observed superconductivity state in the sulfur-hydrogen system at low temperature.
