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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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Published in: | Physica. C, Superconductivity Superconductivity, 1996-06, Vol.264 (1), p.81-94 |
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Main Authors: | , , , , , , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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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. |
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ISSN: | 0921-4534 1873-2143 |
DOI: | 10.1016/0921-4534(96)00237-7 |