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Determination of a mass isotope effect on Tc in an electron-donor-based organic superconductor, κ-(ET) 2Cu(NCS) 2, where ET represents bis(ethylenedithio)tetrathiafulvalene

We describe the first determination of a genuine mass isotope effect on T c arising from the isotopic substitution of atoms in the ET [bis(ethylenedithio)tetrathiafulvalene] molecule of an electron-donor-based organic superconductor, κ-(ET) 2Cu(NCS) 2 ( T c = 9.6 K, inductive onset). The isotopic su...

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Bibliographic Details
Published in:Physica. C, Superconductivity Superconductivity, 1996-06, Vol.264 (1), p.81-94
Main Authors: Kini, A.M., Carlson, K.D., Wang, H.H., Schlueter, J.A., Dudek, J.D., Sirchio, S.A., Geiser, U., Lykke, K.R., Williams, Jack M.
Format: Article
Language:English
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Summary:We describe the first determination of a genuine mass isotope effect on T c arising from the isotopic substitution of atoms in the ET [bis(ethylenedithio)tetrathiafulvalene] molecule of an electron-donor-based organic superconductor, κ-(ET) 2Cu(NCS) 2 ( T c = 9.6 K, inductive onset). The isotopic substitution in the ET molecule involves concurrent replacement of the four carbon atoms in the terminal 1,2-ethanediyl groups with 13C and all eight sulfuir atoms with 34S. This substitution, 13C(4) 34S8), increases the mass of the ET molecule by 20 amu, which is a 5% increase in the normal mass. With the use of AC susceptibility measurements on a large sampling of single crystals, including both undeuterated and fully deuterated salts, we obtain ΔT c = −0.12 ± 0.05 K for this isotope effect. Assuming a BCS-like mass effect with ET as the relevant mass entity ( M), this effect gives α = 0.26 ± 0.11 for T c αM − α . Additionally, our experiments with fully deuterated κ-(ET) 2Cu(NCS) 2 ( 2H replacing eight hydrogen atoms in ET) confirm the occurrence of a large inverse isotope effect for the deuteration, and yield the first definitive value for this effect, ΔT c = +0.28 ± 0.06 K. The isotope effect for 13C(4) 34S(8) substitution, however, is unaffected by deuteration. Contrary to an earlier report by others, we find a zero isotope effect within ±0.06 K for 13C(4) substitution alone.
ISSN:0921-4534
1873-2143
DOI:10.1016/0921-4534(96)00237-7