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TT: Fachverband Tiefe Temperaturen

TT 20: SC: Fabrication and Characterization of Iron-Based and Other Superconductors

TT 20.2: Vortrag

Mittwoch, 24. März 2010, 09:45–10:00, H19

Metal-semiconductor transition and phase separation in superconducting Fe_1+yTe_1−xSe_x single crystals — •Sahana Roessler¹, Dona Cherian², Sasidharan Harikrishnan², Handadi L Bhat², Suja Elizabeth¹, Frank Steglich¹, Steffen Wirth¹, and Liu Hao Tjeng¹ — ¹Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany — ²Department of Physics, Indian Institute of Science, C V Raman Avenue, Bangalore - 560012, India

We have investigated the influence of excess Fe on the electrical transport and magnetism of Fe_1+yTe_1−xSe_x (y = 0.26, 0.15, 0.12 and x =0.32, 0.34, 0.36, respectively) single crystals. All three samples exhibit superconducting transitions with critical temperatures T_c (onset) ∼ 15 K in the resistivity measurements. It has been inferred from the width of the superconducting transition and the magnitude of the lower critical field H_c1, that excess Fe occupying interstitial sites in the chalcogen planes suppresses superconductivity. Further, the temperature dependence of resistivity in the normal state changes from metallic to semiconducting behavior with increasing Fe. From the dc-magnetization, linear and non-linear response of the ac-susceptibility, we show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is due to a magnetic coupling between Fe in the chalcogen planes with those in the Fe-square lattice.