@article{555a1db0bbc5420f904d59ccb09bbdc0,
title = "Off-diagonal interactions and pair-binding in superconducting fullerides",
abstract = "We have examined the effect of including off-diagonal (non-density-density) electron-electron (c-e) interactions on putative electronically-driven superconducting states in the fullerides by studying the spectra of truncated tetrahedral and icosahedral {"}Hubbard molecules{"}. Our perturbation theoretic and exact diagonalization calculations indicate that for moderate screening lengths and intermediate interaction strengths these terms can contribute significantly to pair-binding energies and to energy level splittings, and consequently the occurence of superconductivity in such models is very sensitive to the precise values of the parameters. We illustrate this in detail in the case of C60-2. We also find that, although the individual levels shift substantially, the critical interaction strengths for the Hund's rule violating level crossings are quite insensitive to the inclusion of these additional interactions.",
author = "Campbell, {D. K.} and Gelfand, {M. P.} and Lin, {H. Q.} and Sondhi, {S. L.}",
note = "Funding Information: We have shown that for screenedin teractiontsh e contributionosf termsi nvolvingW and X to the pair-bindinge nergieas ndl evels plittingsa rep rima facie sig-nificanta nd must be considereidn quantitativdei scus-sions of theseo bservables. Concerningth e Hund'sr ule violatingle velcrossings in doublyc hargeda nions,w e find that despites ubstan-tial shifts in individuael nergyl evels,t he critical values of U/t at which the crossingos ccurare surprisingly insensitive to the inclusiono f all the nearest-neighbor interactionsT. his suggesttsh at the effectso f electron correlationms ightbe significanet venfor isolateda n-ions for which pair-bindinigs certainlyru ledout, since the energyd ifferencebs etweend ifferentc harges tates are dominatebdy the {"}moleculacra pacitancee{"}n ergy. In this connectiotnh ework of Negri el al. \[11m\] eritsa closee xamination. On the questiono f pair-bindingw e find that for the expectedv alueso f the parametertsh e W term reduces (using the crude measureo f Upair)b y about 50% the suppressioonf pair-bindinpgr oducedb y the V terma nd bringsU pairv eryc loset o the perturbativree gime.T his suggestsa narrow but non-vanishinrge giono f plausible parameterins which an electronicm echanismco uld explaint he superconductiviitny the dopedf ullerides. Howeverg, ivent hes ensitivitoyf the calculationtso the precisev alueso f thesep arametersw,e feel that micro-scopicc alculationasr el ikelyt o remains uggestivrea ther than definitive\[ 12\]. Acknowledgements We are gratefutlo S. Kivelsonf or usefuld iscussionsT. his work was supportedin part by the NSF grantN o. (DMR89-20538a)n dan allocatioonf supercomputteirm eat the NCSA (DKC and HQL), the MaeArthurC hair at the Universityo f Illinois (MPG) and NSF grant Nos. DMR 91-22385a nd DMR 91-57018( SLS).",
year = "1995",
month = mar,
day = "15",
doi = "10.1016/0379-6779(94)02941-Q",
language = "English (US)",
volume = "70",
pages = "1523--1526",
journal = "Synthetic Metals",
issn = "0379-6779",
publisher = "Elsevier BV",
number = "1-3",
}