Dielectric anomalies and interactions in the 3D quadratic band touching Luttinger semimetal Pr$_2$Ir$_2$O$_7$

TL;DR

This study investigates the dielectric properties and electron interactions in the quadratic band touching semimetal Pr$_2$Ir$_2$O$_7$, revealing strong interactions coexist with Fermi liquid behavior through terahertz spectroscopy.

Contribution

The paper provides the first terahertz spectroscopic measurements of Pr$_2$Ir$_2$O$_7$, demonstrating large dielectric constants and persistent Fermi liquid behavior despite strong electron interactions.

Findings

Dielectric constant reaches ~180 at low temperatures.

Electron interactions are nearly two orders of magnitude larger than kinetic energy.

Fermi liquid state persists with a T^2 scattering rate dependence.

Abstract

Dirac and Weyl semimetals with linearly crossing bands are the focus of much recent interest in condensed matter physics. Although they host fascinating phenomena, their physics can be understood in terms of weakly interacting electrons. In contrast, more than 40 years ago, Abrikosov pointed out that quadratic band touchings are generically strongly interacting. We have performed terahertz spectroscopy on films of the conducting pyrochlore Pr$_2$Ir$_2$O$_7$, which has been shown to host a quadratic band touching. A dielectric constant as large as $\tilde{\varepsilon }/\epsilon_0 \sim 180 $ is observed at low temperatures. In such systems the dielectric constant is a measure of the relative scale of interactions, which are therefore in our material almost two orders of magnitude larger than the kinetic energy. Despite this, the scattering rate exhibits a $T^2$ dependence, which shows that for finite doping a Fermi liquid state survives, however with a scattering rate close to the maximal value allowed.