Berlin 2005 – scientific programme
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TT: Tiefe Temperaturen
TT 3: Correlated Electrons - Heavy Fermions
TT 3.8: Talk
Friday, March 4, 2005, 12:00–12:15, TU H3027
Optical spectroscopy of the mixed valence semiconductor TmSe — •Michael Dumm1, Boris Gorshunov1, Daniel Faltermeier1, Philipp Haas1, Martin Dressel1, and Takeshi Matsumura2 — 11. Physikalisches Institut, Universität Stuttgart, 70550 Stuttgart — 2Physics Department, Tohoku University, Sendai 980-77, Japan
Among mixed-valence compounds TmSe has attracted particular interest because of its unusual physical properties. For instance, beyond unique magnetic properties this semiconductor shows no signs of activated behavior in the temperature dependence of the dc conductivity. We investigated the dynamical conductivity of TmSe at 5 K ≤ T ≤ 300 K by employing infrared and quasi-optical Terahertz techniques in a broad frequency range 10 cm−1 ≤ ν ≤ 10000 cm−1 covering all relevant energy scales. At high temperatures, the optical spectra reveal signatures of a two-component free-carrier response originating on the one hand from light d-electrons and on the other hand from heavy f-electronic states hybridized with the charge carriers in the conduction band. Going towards lower temperatures, the heavy carrier response starts diminishing and a gap-like feature builds up below 100 cm−1. On the basis of a detailed analysis of our optical and dc data, we will discuss the origin of the gap. Furthermore, we will compare the results obtained on TmSe to those measured on other Kondo insulators like YbB12 and SmB6.