Pauli susceptibility of nonadiabatic Fermi liquids

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 chi one of such quantities and show that the nonadiabatic corrections reduce chi with respect to its adiabatic limit. We also show that the nonadiabatic regime induces an isotope dependence of chi, which in principle could be measured.