J. Phys. IV France 114 (2004) 401
Cooling rate dependence of the in-plane magnetic penetration depth in -type BEDT-TTF superconductorsN. Yoneyama1, 1, A. Higashihara1, T. Sasaki1, T. Nojima2 and N. Kobayashi2
1 Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
2 Center for Low Temperature Science, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
We performed dc magnetization measurements under the control of cooling-rate in the organic superconductors -(BEDT-TTF) 2X ( X=Cu(NCS) 2 and Cu[ N(CN) 2] Br). A distinct different cooling-rate dependence of the in-plane magnetic penetration depth ( //(0)) was observed between two salts, where //(0) was estimated from a linear extrapolation to 0 K. In the Cu(NCS) 2 salt, //(0) remains unchanged regardless of cooling-rate, while Tc decreases slightly in faster-cooling. On the other hand, //(0) in the Cu[ N(CN) 2] Br salt becomes long significantly in faster-cooling. We quantitatively explain the change of //(0) in the cooling-rate as an impurity effect by terminal ethylene disorder in BEDT-TTF molecules in terms of the local and clean limit approximation. Key words. Organic superconductor, magnetization, penetration depth, London model.
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