Dresden 2011 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 42: SC: Fe-based Superconductors - Fe(Se,Te)

TT 42.1: Vortrag

Mittwoch, 16. März 2011, 18:45–19:00, HSZ 304

Physical properties of FeSe_0.5Te_0.5 single crystals — •Vladimir Tsurkan^1,2, Joachim Deisenhofer¹, Axel Günther¹, Christian Kant¹, Florian Schrettle¹, Hans-Albrecht Krug von Nidda¹, and Alois Loidl¹ — ¹Experimentalphysik V, Center for Electronic Correlations and Magnetism, Institute for Physics, Augsburg University, D-86135 Augsburg, Germany — ²Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chişinău, Republic of Moldova

We report on structural, magnetic, conductivity, and thermodynamic studies of FeSe_0.5Te_0.5 single crystals grown by self-flux and Bridgman methods. The lowest values of the susceptibility in the normal state, the highest transition temperature T_c of 14.5 K, and the largest heat-capacity anomaly at T_c were obtained for pure (oxygen-free) samples. The upper critical field H_c2 of ∼ 500 kOe is estimated from the resistivity study in magnetic fields parallel to the c-axis. The anisotropy of the upper critical field γ_Hc2 = H_c2^ab/H_c2^c reaches a value ∼ 6 at T—→ T_c. Extremely low values of the residual Sommerfeld coefficient for pure samples indicate a high volume fraction of the superconducting phase (up to 97 %). The electronic contribution to the specific heat in the superconducting state is well described within a single-band BCS model with a temperature dependent gap Δ₀ = 27(1) K. A broad cusp-like anomaly in the electronic specific heat of samples with suppressed bulk superconductivity is ascribed to a splitting of the ground state of the Fe²⁺ ions at 2c sites. This contribution is fully suppressed in the ordered state in samples with bulk superconductivity.