Mobility gap in intermediate valent TmSe

TL;DR

This study investigates the infrared optical conductivity of TmSe, revealing a temperature-dependent mobility gap caused by electron localization, distinct from a hybridization gap, highlighting complex electronic interactions in intermediate valence compounds.

Contribution

It provides new insights into the temperature-dependent electronic structure of TmSe, distinguishing a mobility gap from hybridization effects in intermediate valence materials.

Findings

Observation of hybridization signatures in optical conductivity.

Identification of a mobility gap at low temperatures.

Temperature-dependent crossover in electronic behavior.

Abstract

The infrared optical conductivity of intermediate valence compound TmSe reveals clear signatures for hybridization of light $d$- and heavy f-electronic states with m* ~ 1.6 m_0 and m* ~ 16 m_0, respectively. At moderate and high temperatures, the metal-like character of the heavy carriers dominate the low-frequency response while at low temperatures (T_N < T < 100 K) a gap-like feature is observed in the conductivity spectra below 10 meV which is assigned to be a mobility gap due to localization of electrons on local Kondo singlets, rather than a hybridization gap in the density of states.