Nonadiabatic Pauli susceptibility in fullerene compounds

Abstract

Pauli paramagnetic susceptibility χ is unaffected by the electron-phonon interaction in the MigdalEliashberg context. Fullerene compounds however do not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic effects are expected to be relevant in these materials. In this paper we investigate the Pauli spin susceptibility in nonadiabatic regime by following a conserving approach based on Ward's identity. We find that a sizable renormalization of χ due to electron-phonon coupling appears when nonadiabatic effects are taken into account. The intrinsic dependence of χ on the electron-phonon interaction gives rise to a finite and negative isotope effect which could be experimentally detected in fullerides. In addition, we find an enhancement of the spin susceptibility with temperature increasing, in agreement with the temperature dependence of χ observed in fullerene compounds. The role of electronic correlation is also discussed. PACS number(s): 74.70. Wz, 63.20.Kr

Recent Advances in Fullerene Superconductivity

“…The superconducting phases adopt, in general, either face-centered-cubic (fcc) or primitive cubic structures, in which the three cations occupy the available octahedral and tetrahedral interstitial sites. Charge transfer is essentially complete and the conduction band of C 60 ; which arises from its lowest unoccupied molecular orbital (LUMO) of t 1u symmetry is half filled (Fig. 1).…”

“…The high electron affinity of C 60 and the weak intermolecular van der Waals forces between the molecules in the crystal make it an excellent potential host for reductive intercalation chemistry. Indeed, intercalation of solid C 60 with electron donors, like the alkali metals, results in a wealth of intercalated fulleride salts with stoichiometries A x C 60 ; where x can be as low as 1 (CsC 60 ) or as high as 12 (Li 12 C 60 ).…”

“…Indeed, intercalation of solid C 60 with electron donors, like the alkali metals, results in a wealth of intercalated fulleride salts with stoichiometries A x C 60 ; where x can be as low as 1 (CsC 60 ) or as high as 12 (Li 12 C 60 ). This reflects the ease of reduction of C 60 ; especially to oxidation states ranging from À1 to À6:…”

“…Changing the size and nature of the dopants affects sensitively the superconducting properties of the materials (4), culminating in the recent observation of high temperature superconductivity at 117 K in hole-doped C 60 derivatives (5). Another remarkable discovery has been the reaction of C 60 with the strong organic donor tetrakis(dimethylamino)ethylene, (TDAE), resulting in the formation of a ferromagnetic solid, ðTDAEÞC 60 ; with a 16 K Curie temperature (6). Finally, an unexpected discovery in this field has been the ease with which C 60 units can bond together, giving rise to polymerized fullerene networks with novel structural architectures.…”

HighTcSuperconductivity inMgB2by Nonadiabatic Pairing

“…The detection of isotope effects on various quantities receives a crucial importance in the nonadiabatic framework since it directly probes the nonadiabatic nature of el-ph interaction. In particular it has been shown that nonadiabatic effects give rise to a finite isotope effect on quantities which in conventional ME theory are expected to not show it, for instance the effective electron mass m * [29] and the spin susceptibility χ [30]. The actual discovery of an anomalous isotope effects on these or other quantities represents therefore a precise prediction of the nonadiabatic theory which could be experimentally checked.…”