Quasiparticle interference in heavy Fermion superconductor CeCoIn_5

TL;DR

This study proposes using quasiparticle interference spectroscopy via STM to directly determine the d-wave gap symmetry in CeCoIn_5, resolving previous ambiguities and providing a real-space fingerprint of the superconducting gap.

Contribution

It introduces a direct STM-based method to identify the superconducting gap symmetry in heavy Fermion superconductors, specifically CeCoIn_5, by analyzing QPI patterns for different d-wave symmetries.

Findings

QPI patterns differ for d_{xy} and d_{x^2-y^2} symmetries

Characteristic differences in QPI can be identified by STM

Method offers a direct way to determine gap symmetry

Abstract

We investigate the quasiparticle interference in the heavy Fermion superconductor CeCoIn_5 as direct method to confirm the d-wave gap symmetry. The ambiguity between d_{xy} and d_{x^2-y^2} symmetry remaining from earlier specific heat and thermal transport investigations has been resolved in favor of the latter by the observation of a spin resonance that can occur only in d_{x^2-y^2} symmetry. However these methods are all indirect and depend considerably on theoretical interpretation. Here we propose that quasiparticle interference (QPI) spectroscopy by scanning tunneling microscopy (STM) can give a direct fingerprint of the superconducting gap in real space which may lead to a definite conclusion on its symmetry for CeCoIn_5 and related 115 compounds. The QPI pattern for both magnetic and nonmagnetic impurities is calculated for the possible d-wave symmetries and characteristic differences are found that may be identified by STM method.