J. Phys. IV France
Volume 114, April 2004
Page(s) 211 - 215

J. Phys. IV France
114 (2004) 211
DOI: 10.1051/jp4:2004114046

London penetration depth in (BEDT-TTF) 2 superconductors

R.W. Giannetta1, D.D. Lawrie1, A. Carrington2, R. Prozorov3, J.A. Schlueter4, A.M. Kini4, U. Geiser4, J. Mohtasham5, R.W. Winter5 and G.L. Gard5

1  Loomis Laboratory of Physics, Univ. of Illinois at Urbana-Champaign, 1110 W. Green, Urbana, Il 61801, USA
2  Dept. of Physics, Univ. of Bristol, Bristol, UK
3  Dept. of Physics and Astronomy, Univ. of South Carolina, Columbia, SC 29208, USA
4  Materials Science Division, Argonne National Laboratory, Argonne, Il 60439, USA
5  Department of Chemistry, Portland State University, Portland, OR 97207, USA

Measurements of the London penetration depth, $\lambda
$ (T), are reported for crystals of superconducting $\kappa $-(ET) 2 Cu[ N(CN) 2] Br (T C = 11.6 K) and $\beta
''$ -(ET) 2-SF 5CH 2CF 2SO 3 (T C = 5.2 K) at temperatures down to 0.35 K. For $\kappa $-(ET) 2 Cu[ N(CN) 2] Br the superfluid density shows the power law behavior characteristic of nodal quasiparticles with impurity scattering. The rate of change of superfluid density with temperature is higher than predicted by a weak-coupling d-wave model and higher than observed in the copper oxides. The in-plane penetration depth consistently shows a T 3/2 dependence while the interplane penetration depth varies as T 1.22. Measurements in $\beta
''$ -(ET) 2-SF 5CH 2CF 2SO 3 also show power law behavior consistent with nodal quasiparticles but with greater impurity scattering than in $\kappa $-(ET) 2 Cu[ N(CN) 2] Br. Key words. penetration depth - order parameter - organic superconductor - superfluid density.

© EDP Sciences 2004