Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 9: SC: Poster Session
TT 9.21: Poster
Montag, 22. März 2010, 14:00–18:00, Poster A
Nernst Effect in LaFeAsO1−xFx — •Agnieszka Kondrat1, Jorge Enrique Hamann-Borrero1, Norman Leps1, Martin Kosmala2, Olaf Schumann2, Jochen Werner1, Guenter Behr1, Markus Braden2, Ruediger Klingeler1, Christian Hess1, and Bernd Buechner1 — 1IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany — 2II. Physikalisches Institut, Universitaet zu Koeln, 50937 Koeln, Germany
We report a study on electrical resistivity, thermoelectric power, Hall effect and Nernst coefficient of polycrystalline LaFeAsO1−xFx in the temperature range 5-300 K and magnetic field 14 T. We show the evolution of transport properties with electron doping (F content x=0, 0.05, 0.1). The parent compound undergoes two phase transitions at the temperature around 150 K: magnetic to antiferromagnetically ordered spin density wave state and structural - from tetragonal to orthorombic crystal structure. The presence of phase transitions gives rise to changes in charge carrier scattering processes, which is reflected as profound anomalies in investigated transport properties. In the superconducting samples these two transitions are not present, nevertheless in the underdoped compound (x=0.05) we observe features reminiscent of the transitions, in particular change of slope in electrical resistivity and Nernst signal. We discuss the possibility of presence of spin fluctations, which lead to formation of SDW state in parent compound and to anomalies in transport properties in underdoped superconducting samples. At the same time the optimally doped sample (x=0.1) does not show any of these characteristic features.