Odd Frequency Pairing in the Kondo Lattice

TL;DR

This paper explores the theoretical possibility of odd-frequency triplet pairing in heavy fermion superconductors using a toy model, revealing stable states with unique gapless excitations and specific thermodynamic signatures.

Contribution

It introduces a novel mean field approach employing Majorana representation to model odd-frequency pairing in the Kondo lattice, demonstrating stable triplet superconducting states.

Findings

Stable odd-frequency triplet superconducting state identified

Surface states exhibit gapless excitations with linear energy dependence

Coexistence of T^3 NMR relaxation rate and linear specific heat

Abstract

We discuss the possibility that heavy fermion superconductors involve odd-frequency pairing of the kind first considered by Berezinskii. Using a toy model for odd frequency triplet pairing in the Kondo lattice we are able to examine key properties of this new type of paired state. To make progress treating the strong $n_f=1$ constraint in the Kondo lattice model we use the technical trick of a Majorana representation of the local moments, which permits variational treatments of the model without a Gutzwiller approximation. The simplest mean field theory involves the development of bound states between the local moments and conduction electrons, characterized by a spinor order parameter. We show that this state is a stable realization of odd frequency triplet superconductivity with surfaces of gapless excitations whose spin and charge coherence factors vanish linearly in the quasiparticle energy. A $T^3$ NMR relaxation rate coexists with a linear specific heat. We discuss possible extensions of our toy model to describe heavy fermion superconductivity.