Elementary excitations and elusive superconductivity in palladium hydride -- \textit{ab initio} perspective. II. Phonons

Motivated by a experimental reports on possible high temperature superconductivity in palladium hydride [Tripodi et al., \textit{Physica C} \textbf{388-389}, 571 (2003)], we present a first principle study of spin fluctuations, electron-phonon coupling and critical temperature ($T_{c}$) in PdH$_{x}$ , $0 < x < 1$. Our results described in terms of (i) electronic structure, (ii) phonon density of states and (iii) Eliashberg function show that the hydrogenation of Pd clearly enhance the electron-phonon coupling in this material. Assuming phonons to be the driving force for superconductivity, fcc Pd features a vanishingly small $T_{c}$, while for the stochiometric $x=1$ PdH the resulting $T_{c}$ is around 10K in agreement with experiment. It is generally believed [Berk \& Schrieffer, \textit{Phys. Rev. Lett.}, \textbf{17}, 433 (1966)] that intense spin-\&flip fluctuations of Pd are destructive for the conventional, i.e. $s$-wave, superconductivity. However, the H doping leads to a drastic reduction of spin-flip scattering. Please look for complementary presentation of Pawe\l{} Buczek.