Dynamical magnetic response in superconductors with finite momentum pairs

TL;DR

This paper derives the dynamical magnetic response in superconductors with finite-momentum pairs, revealing how quasiparticle excitations and symmetry-breaking influence magnetic susceptibility and related phenomena.

Contribution

It provides a theoretical framework for understanding magnetic responses in Fulde-Ferrell superconductors with finite pair momentum, including effects on Knight shift and spin resonance.

Findings

Finite pair momentum causes segmentation into paired and unpaired regions.

Dynamical susceptibility exhibits characteristic symmetry-breaking behavior.

Finite-q pairing influences Knight shift and spin resonance formation.

Abstract

We derive the dynamical magnetic response functions in the Fulde-Ferrell (FF) state of a superconductor with inversion symmetry. The pair momentum 2q is obtained by minimization of the condensation energy and the resulting quasiparticle states and spectral functions exhibit the segmentation into paired and unpaired regions due to the finite q. The dynamical magnetic susceptibility is then calculated in linear response formalism in the FF state with finite-q condensate resulting from s-wave or d-wave pairing. We show that quasiparticle excitations inside as well as between paired and unpaired segments contribute to the dynamical response. We discuss its dependence on frequency and momentum transfer which develops a characteristic symmetry-breaking parallel to q. Furthermore, we investigate the possible influence on Knight shift and in the case of d-wave pairing on the spin resonance formation in the FF state.