Possibility for the anisotropic acoustic plasmons in LaH10 and their role in enhancement of the critical temperature of superconducting transition

Abstract

We discuss a possible role of the collective acoustic electronic excitations in the mechanism of the nearly room-temperature superconductivity in superhydrides at megabar pressures. While the dominant role of the phonon mechanism of superconductivity in such compounds is evident due to the measured isotope effect with deuterium (on LaD10), the small values of the effective Coulomb constant chosen in theoretical calculations of the critical temperature deserve further justification. We believe that the additional suppression of the Coulomb repulsion in superhydrides may be due to the appearance of additional acoustic plasmonic branches in their collective spectra. In LaH10 the conditions for such mechanism arise due to the hybridization of La 4f and H 1s states near the Fermi level in the vicinity of the L point of the Brillouin zone. We propose an analytical model approximation for the resulting conducting band and show that in a certain range of directions in quasimomentum space an acoustic branch should appear in the spectrum of the collective electronic excitations in LaH10. The contribution of these excitations to the suppression of the effective Coulomb constant is analyzed.