Low energy electrodynamics of the Kondo-lattice antiferromagnet CeCu$_2$Ge$_2$

TL;DR

This study uses THz spectroscopy and DC resistivity to analyze the low-energy electrodynamics of CeCu$_2$Ge$_2$, revealing large mass renormalization in its magnetic state consistent with thermodynamic data.

Contribution

It provides the first detailed low-energy electrodynamics characterization of CeCu$_2$Ge$_2$ in its magnetic state using time-domain THz spectroscopy.

Findings

Formation of a narrow Drude-like peak at low temperatures

Evidence of large mass renormalization in the magnetic state

Agreement of mass enhancement with thermodynamic measurements

Abstract

We present time-domain THz spectroscopy data of a thin film of the Kondo-lattice antiferromagnet CeCu$_2$Ge$_2$. The low frequency complex conductivity has been obtained down to temperatures below the onset of magnetic order. At low temperatures a narrow Drude-like peak forms, which is similar to ones found in other heavy fermion compounds that do not exhibit magnetic order. Using this data in conjunction with DC resistivity measurements, we obtain the frequency dependence of the scattering rate and effective mass through an extended Drude model analysis. The zero frequency limit of this analysis yields evidence for large mass renormalization even in the magnetic state, the scale of which agrees closely with that obtained from thermodynamic measurements.