Glass-like transition in ${\kappa} $-(ET)${_{2}}$Cu[ N(CN)${_{2}}$] Br at T${_{g}}$ ${\sim }$ 75 K – implications for the superconducting ground-state properties

J. Müller; M. Lang; F. Steglich; J.A. Schlueter

doi:doi:10.1051/jp4:2004114077

Issue		J. Phys. IV France Volume 114, April 2004


Page(s)		341 - 342
DOI		https://doi.org/10.1051/jp4:2004114077

J. Phys. IV France 114 (2004) 341
DOI: 10.1051/jp4:2004114077

Glass-like transition in ${\kappa}$ -(ET) ₂Cu[ N(CN) ₂] Br at T _g ${\sim }$ 75 K - implications for the superconducting ground-state properties

J. Müller^{1, 1}, M. Lang², F. Steglich¹ and J.A. Schlueter³

¹ Max-Planck-Institute for Chemical Physics of Solids, 01187 Dresden, Germany
² J.W. Goethe University, FOR 412, 60054 Frankfurt, Germany
³ Argonne National Laboratory, Illinois 60439, USA

Abstract
High-resolution measurements of the linear coefficients of thermal expansion, $\alpha _{\rm i}$ (T), on ${\kappa}$ -(ET) ₂Cu[ N(CN) ₂] Br reveal large, step-like anomalies at temperatures around 75 K. These have been identified as a kinetic, glass-like transition, where below a certain temperature T $_{\rm g}$ a characteristic disorder in the orientational degrees of freedom of the donor molecule's ethylene endgroups becomes frozen. The phenomenology of this relaxation process provides a natural explanation for the observed time and cooling-rate dependences of the ground-state properties in this system. Furthermore, the data suggest that the degree of disorder in the sample can be varied in a controlled way by controlling the cooling rate as well as the applied pressure. Key words. Organic superconductors - BEDT-TTF salts - thermal expansion - disorder.

Glass-like transition in -(ET) 2Cu[ N(CN) 2] Br at T g 75 K - implications for the superconducting ground-state properties

Glass-like transition in ${\kappa}$ -(ET) ₂Cu[ N(CN) ₂] Br at T _g ${\sim }$ 75 K - implications for the superconducting ground-state properties