The central bond {sup 13}C{double_bond}{sup 13}C isotope effect for superconductivity in the high-T{sub c} {beta}*-(ET){sub 2}I{sub 3} phase and its implications regarding the superconducting pairing mechanism in TTF-based organic superconductors

Conference · Tue Sep 01 04:00:00 EDT 1992

OSTI ID:10179014

Carlson, K D; Williams, J M; Geiser, U; Kini, A M; Wang, H H; Klemm, R A; Kumar, S K; Schlueter, J A; Ferraro, J R; Lykke, K R; Wurz, P; Sutin, J D.B. ^[1]; Parker, D H ^[1]; Schirber, J E; Venturini, E L ^[2]; Stout, P ^[3]

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1. Argonne National Lab., IL (United States)
2. Sandia National Labs., Albuquerque, NM (United States)
3. Bio-Rad, Cambridge, MA (United States). Digilab Division

We report a new study, based on magnetization measurements, of the isotope effect for {sup 13}C substitution in the electronically active central double-bonded carbon atoms (C=C) of the TTF moiety of ET [bis(ethylenedithio)tetrathiafulvalene] in {beta}*-(ET){sub 2}I{sub 3} which is the crystallographically ordered form of {beta}-(ET){sub 2}I{sub 3} produced by application of pressure. A recent report by Merzhanov et al. [C. R. Acad. Sci., Paris, 314, 563 (1992)] has shown that this same {sup C} substitution leads to a ``giant`` isotope effect ({Delta}{Tc} = {minus} 0.6 K) in resistive determinations of {Tc} ({approximately} 8 K) for {beta}-(ET){sub 2}I{sub 3}, which lends experimental support to a theory by Yamaji [Solid State Common., 61, 413. (1987)] for salts of TTF-analogue donor molecules that includes optical phonons of symmetric intramolecular vibrations as a source of mediation for superconducting pairing of charge-carriers. In contrast to this result, our study shows the absence of an isotope effect within a precision of {plus_minus} 0.1 K.({approximately} l%), indicating that the central atom C=C stretching motion ({approximately} 1500 cm{sup {minus}1}) of ET cannot be a dominant mechanism for phonon exchange. Our results are consistent with those of a very recent study of the same isotope effect for {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br and {kappa}-(ET){sub 2}Cu(NCS){sub 2} [Inorg. Chem., 32, 3356 (1992)].

• Research Organization: Argonne National Lab., IL (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-31109-ENG-38; AC04-76DP00789
• OSTI ID: 10179014
• Report Number(s): ANL/CP--75668; CONF-920850--1; ON: DE92040725
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360607
665411
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BEDT-TTF
CARBON 13
DOUBLE BONDS
ISOTOPE EFFECTS
MAGNETIZATION
ORGANIC SUPERCONDUCTORS
PHONONS
SUPERCONDUCTIVITY
TRANSITION TEMPERATURE