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Jeudi 17 Janvier 2013, 14h
Amphi Howleck, Esc C, 1ème etage
Bismuth chalcogenides : thermoelectricity, surface states and optical properties
Ana Akrap
Université de Geneve
Bismuth chalcogenides are well-known thermoelectric materials [1]. These semiconductors have recently regained popularity as it was discovered that they host metallic surface states [2]. However, the bulk conduction still dominates the transport properties. Why are the resistivities so low ? Can this be improved ? What is the role of the surface states in the electronic transport ? To answer these questions, I will present and discuss transport and optical spectroscopy measurements done on a series of compounds Bi_2Te_3-xSe_x. In a second part, I will talk about BiTeI, a non centrosymmetric giant Rashba splitting system [3], in which topological surface states have been predicted under high pressure [4]. Using high-pressure infrared and Raman spectroscopy we investigated the phase diagram of this compound and found evidence of a pressure-induced first order phase transition.
[1] H. Goldsmid, Thermoelectric Refrigeration (Temple Press Books Ltd, London, 1964).
[2] H. Zhang, C.-X. Liu, X.-L. Qi, X. Dai, Z. Fang, and S.-C. Zhang, Nature Phys. 5, 438 (2009).
[3] K. Ishizaka et al., Nature Materials 10, 521 (2011).
[4] M. S. Bahramy, B.-J. Yang, R. Arita, and N. Nagaosa, Nature Communications 3, 679 (2012).