J. Phys. IV France
Volume 114, April 2004
Page(s) 363 - 365

J. Phys. IV France
114 (2004) 363
DOI: 10.1051/jp4:2004114084

The origin of the difference in the superconducting critical temperatures of the ${\beta_{\rm H}}$ and ${\beta_{\rm L}}$ phases of (BEDT-TTF) 2I 3

B.J. Powell

Department of Physics, University of Queensland, Brisbane, Queensland 4072, Australia

Incommensurate lattice fluctuations are present in the $\beta_\textrm{L}$ phase ( $T_c\sim1.5$ K) of ET 2I 3 (where ET is BEDT-TTF - bis(ethylenedithio)tetrathiafulvalene) but are absent in the $\beta_\textrm{H}$ phase ( $T_c\sim7$ K). We propose that the disorder in the conformational degrees of freedom of the terminal ethylene groups of the ET molecules, which is required to stabilise the lattice fluctuations, increases the quasiparticle scattering rate and that this leads to the observed difference in the superconducting critical temperatures, Tc, of the two phases. We calculate the dependence of Tc on the interlayer residual resistivity. Our theory has no free parameters. Our predictions are shown to be consistent with experiment. We describe experiments to conclusively test our hypothesis.

© EDP Sciences 2004