Universal inverse deuterium isotope effect on the T{sub c} of BEDT-TTF based molecular superconductors.
Deuterium substitution of the ethylene end groups of the ET [ET: BEDT-TTF or bis(ethylenedithio)tetrathiafulvalene] electron-donor molecule results in a 0.25 K increase in the superconducting transition temperature of three molecular superconductors derived from this molecule. Simplistically speaking, this change in T{sub c} is in contradiction to that predicted by the electron-phonon coupling mechanism of the BCS theory. We suggest that the slight shortening of the C-D bond relative to the C-H bond, coupled with the recent findings of a large, negative uniaxial pressure derivative of T{sub c} in {kappa}-(ET){sub 2}Cu(SCN){sub 2} and {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}, can explain this unique effect. Herein we report the first study of the effect of deuterium substitution on the superconducting transition temperature in a molecular-based superconductor in which the electron-donor molecules are packed in a {beta}' motif, viz., {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}. This compound is ideally suited for this study because it contains discrete (non-polymeric) anions, has a completely ordered structure, is indefinitely stable in air at room temperature, and is free from possible magnetic impurities. Substitution of the eight hydrogen atoms of the ET molecule by deuterium causes the T{sub c} of {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} to increase from 4.34{+-}0.05 to 4.61{+-}0.03 K. These values were determined by measuring several representative crystals from various parallel electrocrystallization experiments containing h{sub 8}- or d{sub 8}-ET that was prepared in parallel syntheses. This is the first example which demonstrates that the inverse (positive) isotope effect previously observed in {kappa}-phase salts is also present in a {beta}'-phase superconductor.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF); OUS
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 942940
- Report Number(s):
- ANL/CHM/JA-36101; PHYCE6; TRN: US201002%%448
- Journal Information:
- Physica C, Vol. 351, Issue 3 ; Apr. 1, 2001; ISSN 0921-4534
- Country of Publication:
- United States
- Language:
- ENGLISH
Similar Records
Comparison of the crystal and electronic structures of three 2:1 salts of the organic donor molecule BEDT-TTF with pentafluorothiomethylsulfonate anions SF{sub 5}CH{sub 2}SO{sub 3}{sup {minus}}, SF{sub 5}CHFSO{sub 3}{sup {minus}}, and SF{sub 5}CF{sub 2}SO{sub 3}{sup {minus}}
Crystal structure, physical properties and electronic structure of a new organic conductor B"-(BEDT-TTF){sub 2}SF{sub 5}CHFCF{sub 2}SO{sub 3}.