Superconductivity and fractionalized magnetic excitations in CeCoIn5

TL;DR

This paper investigates CeCoIn5's unconventional superconductivity and quantum criticality, providing experimental neutron scattering data and a theoretical framework linking spin fractionalization to superconductivity.

Contribution

It offers the first detailed neutron scattering analysis of CeCoIn5 across Tc and develops a Kondo-lattice model incorporating FL* physics to explain the data.

Findings

Persistent spin excitation continuum in normal state.

Reproduction of key spectral features by the FL* based model.

Unified explanation linking spin fractionalization and superconductivity.

Abstract

Recent experiments on CeCoIn5 -- a prototypical d-wave superconductor -- indicate that its normal state lies near an unconventional quantum critical point (QCP). One intriguing hypothesis is that quantum-critical fluctuations promote fractionalization of localized 4f moments into fermionic spinons. This fractionalized Fermi liquid (FL*) scenario provides a comprehensive framework for the unconventional QCP and superconductivity, and can reconcile a "missing" Fermi-surface volume relative to the Luttinger count in the normal state of CeCoIn5. To test this possibility, we performed inelastic neutron scattering (INS) measurements on CeCoIn5 across the superconducting transition and corresponding theoretical analysis. Our high-precision spectra reveal detailed momentum and temperature dependence of the spin resonance and a structured spin excitation continuum persisting even in the normal state, placing stringent constraints on the physical picture of pairing in a d-wave superconductor. We show that a Kondo-lattice framework incorporating proximity to FL* physics and d-wave pairing reproduces key features of the data. The model suggests that both the quasi-localized nature of the f-moments above Tc and the resonance below Tc arise from common underlying gauge dynamics, implying a unifying organizing principle linking spin fractionalization and unconventional superconductivity in strongly correlated metals.