Superfluid response in heavy fermion superconductors

TL;DR

This paper develops a formalism for superfluid density response in heavy fermion superconductors, emphasizing the role of Kondo-screened quasiparticles, and compares theoretical results with experiments on CeCoIn5 and Yb-doped variants.

Contribution

It derives a superfluid response function in the Kondo-Heisenberg model, highlighting the importance of coupling electromagnetic fields directly to heavy fermion quasiparticles.

Findings

The superfluid density formula aligns well with experimental data.

Doping induces a transition in pairing symmetry.

The formalism includes effects of impurities and non-local electrodynamics.

Abstract

Motivated by recent London penetration depth measurement [H. Kim et al. Phys. Rev. Lett. \textbf{114}, 027003 (2015)] and novel composite pairing scenario [O. Erten, R. Flint and P. Coleman, Phys. Rev. Lett. \textbf{114}, 027002 (2015)] on Yb-doped heavy fermion superconductor CeCoIn$_{5}$, we revisit the issue of superfluid response in microscopic heavy fermion lattice model. However, it is found that in literature explicit expression of superfluid response function in heavy fermion superconductor is rare. In this paper, we make a contribution to this issue by investigating superfluid density response function in celebrated Kondo-Heisenberg model. To be specific, we derive corresponding formalism from an effective fermionic large-N mean-field pairing Hamiltonian, whose pairing interaction is assumed to originate from effective local antiferromagnetic exchange interaction. Interestingly, it is found that physically correct superfluid density formula can only be obtained if external electromagnetic field is directly coupled to heavy fermion quasi-particle. Such unique feature emphasizes the key role of Kondo-screening-renormalized quasi-particle for low-temperature/energy thermodynamics and transport behaviors. As an important application, the theoretical result is compared to experimental measurement in heavy fermion superconductor CeCoIn$_{5}$ and Yb-doped Ce$_{1-x}$Yb$_{x}$CoIn$_{5}$, where the agreement is fairly good and the transition of pairing symmetry in the latter one is explained as a simple doping effect. In addition, the requisite formalism for the commonly encountered nonmagnetic impurity and non-local electrodynamic effect are developed.