Mobility gap in intermediate valentM. Dumm1, B. Gorshunov1, 2, M. Dressel1 and T. Matsumura3
1 1. Physikalisches Institut, Universität Stuttgart Pfaffenwaldring 57, 70550 Stuttgart, Germany
2 General Physics Institute - Moscow, Russia
3 Department of Physics, Graduate School of Science, Tohoku University Sendai 980-8578, Japan
received 2 May 2005; accepted in final form 3 August 2005
published online 31 August 2005
The infrared optical conductivity of the intermediate-valence compound TmSe reveals clear signatures for hybridization of light d- and heavy f-electronic states with and , respectively. At moderate and high temperatures, the metal-like character of the heavy carriers dominates the low-frequency response while at low temperatures ( ) a gap-like feature is observed in the conductivity spectra below 10 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.
71.28.+d - Narrow-band systems; intermediate-valence solids.
75.30.Mb - Valence fluctuation, Kondo lattice, and heavy-fermion phenomena.
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