Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session

TT 33.2: Poster

Wednesday, March 28, 2012, 15:00–19:00, Poster B

Temperature dependent ellipsometric Studies on Iron-Pnictides — •Mathias Eichler, Dan Wu, Bruno Gompf, and Martin Dressel — 1. Physikalisches Institut, Universität Stuttgart

Iron-pnictides indicate a strong temperature dependence in their optical properties even at high energies. The aim of the present work is spectroscopic ellipsometry measurements on iron-pnictides performed as a function of temperature. To accomplish this task we use a Woollam Variable Angle Spectroscopic Ellipsometer (VASE) operating in the spectroscopic range from 4,000cm⁻¹ to 40,000cm⁻¹. The setup is equipped with a customized Janis ST-400 liquid helium cryostat that allows us to measure at temperatures down to 5 K. In order to measure small samples with 1 × 1 mm² in size the setup was improved by upgrading the sample stage geometry to yield an undisturbed signal. The final design also allows us to compensate thermal expansion effects and to easily align the crystal within the cryostat. With this advanced setup, we have investigated several families of 122-pnictides, for example the series EuFe₂(As_1−xP_x)₂. We find a significant shift of the spectral weight with temperature. The results on other compounds will be also discussed, e.g. different doping levels.