Europhys. Lett.
Volume 72, Number 1, October 2005
Page(s) 103 - 109
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 31 August 2005
Europhys. Lett., 72 (1), pp. 103-109 (2005)
DOI: 10.1209/epl/i2005-10207-y

Mobility gap in intermediate valent $\chem{TmSe}$

M. 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 $m^*\approx1.6m_0$ and $m^*\approx16m_0$, respectively. At moderate and high temperatures, the metal-like character of the heavy carriers dominates the low-frequency response while at low temperatures ( $T_{\ab{N}}<T<100$$\un{K}$) a gap-like feature is observed in the conductivity spectra below 10$\un{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.

71.28.+d - Narrow-band systems; intermediate-valence solids.
75.30.Mb - Valence fluctuation, Kondo lattice, and heavy-fermion phenomena.

© EDP Sciences 2005