Anisotropic optical conductivity of the putative Kondo insulator CeRu$_4$Sn$_6$

TL;DR

This study investigates the anisotropic optical properties of CeRu$_4$Sn$_6$, revealing a pseudogap and directional electronic responses characteristic of Kondo insulators through experimental and theoretical approaches.

Contribution

It provides the first detailed analysis of anisotropic optical conductivity in a non-cubic Kondo insulator using combined experimental and theoretical methods.

Findings

Identification of an anisotropic energy pseudogap in CeRu$_4$Sn$_6$

Evidence of Kondo insulator-like behavior in the $a-a$ plane

More metallic response along the c axis

Abstract

Kondo insulators and in particular their non-cubic representatives have remained poorly understood. Here we report on the development of an anisotropic energy pseudogap in the tetragonal compound CeRu$_4$Sn$_6$ employing optical reflectivity measurements in broad frequency and temperature ranges, and local density approximation plus dynamical mean field theory calculations. The calculations provide evidence for a Kondo insulator-like response within the $a-a$ plane and a more metallic response along the c axis and qualitatively reproduce the experimental observations, helping to identify their origin.