Interplane and intraplane heat transport in quasi two-dimensional nodal superconductors

TL;DR

This paper investigates the anisotropic thermal conductivity in quasi-two-dimensional nodal superconductors, proposing extended models to better match experimental data and exploring implications for the superconducting gap symmetry.

Contribution

It introduces two extended models for the superconducting gap and interplane tunneling to explain thermal conductivity anisotropy in CeIrIn_5.

Findings

Simple Fermi surface model is insufficient to explain data.

Extended models with gap modulation and tunneling dependence fit observations.

Comparison with horizontal line nodes model suggests different gap symmetries.

Abstract

We analyze the behavior of the thermal conductivity in quasi-two dimensional superconductors with line nodes. Motivated by measurements of the anisotropy between the interplane and intraplane thermal transport in CeIrIn_5 we show that a simple model of the open Fermi surface with vertical line nodes is insufficient to describe the data. We propose two possible extensions of the model taking into account a) additional modulation of the gap along the axial direction of the open Fermi surface; and b) dependence of the interplane tunneling on the direction of the in-plane momentum. We discuss the temperature dependence of the thermal conductivity anisotropy and its low T limit in these two models and compare the results with a model with a horizontal line of nodes (``hybrid gap''). We discuss possible relevance of each model for the symmetry of the order parameter in CeIrIn_5, and suggest further experiments aimed at clarifying the shape of the superconducting gap.