Field induced spin exciton doublet splitting in d_{x^2-y^2}-wave 115-heavy electron superconductors

TL;DR

This paper presents a theoretical model explaining the field-dependent splitting of spin-exciton modes in heavy fermion superconductor CeCoIn_5, accounting for anisotropic g-factors and quasiparticle interactions, with predictions for nonlinear behavior at high fields.

Contribution

The study introduces a model that naturally explains the observed splitting of the spin exciton doublet in CeCoIn_5 under in-plane magnetic fields, highlighting the role of spin anisotropy.

Findings

Splitting of the spin exciton doublet occurs for in-plane fields due to anisotropic g-factors.

No splitting occurs for fields along the tetragonal axis, only broadening.

Predicted nonlinear splitting behavior at higher magnetic fields.

Abstract

We investigate the spin-exciton modes in the superconducting d_{x^2-y^2} state of CeMIn_5 heavy fermion compounds found at the antiferromagnetic wave vector by inelastic neutron scattering. We present a theoretical model that explains the field dependence for both field directions. We show that the recently observed splitting of the spin exciton doublet in CeCoIn_5 into two non-degenerate modes for in-plane field appears naturally in this model. This is due to the spin anisotropy of g- factors and quasiparticle interactions which lead to different resonant conditions for the dynamic susceptibility components. We predict that the splitting of the spin resonance doublet becomes strongly nonlinear for larger fields when the energy of both split components decreases. For field along the tetragonal axis no splitting but only a broadening of the resonance is found in agreement with experiment.