Pauli susceptibility of nonadiabatic Fermi liquids

Abstract

The nonadiabatic regime of the electron-phonon interaction leads to behaviors of some physical measurable quantities qualitatively different from those expected from the Migdal-Eliashberg theory. Here we identify in the Pauli paramagnetic susceptibility $χ$ one of such quantities and show that the nonadiabatic corrections reduce $χ$ with respect to its adiabatic limit. We show also that the nonadiabatic regime induces an isotope dependence of $χ$, which in principle could be measured.