Coupling to haloform molecules in intercalated C60?

TL;DR

This paper investigates whether intercalated haloform molecules in C60 superconductors enhance Tc through electron coupling, concluding that such coupling is likely minimal and structural effects at interfaces are more influential.

Contribution

The study provides a detailed analysis showing minimal coupling between conduction electrons and intercalated haloform molecules in C60, challenging previous assumptions about their role in Tc enhancement.

Findings

Coupling via hybridization of molecular levels is very small.

Dipole moment coupling is negligible.

Interface structure alterations likely influence Tc more than molecular coupling.

Abstract

For field-effect-doped fullerenes it was reported that the superconducting transition temperature Tc is markedly larger for C60.2CHX_3 (X=Cl, Br) crystals, than for pure C60. Initially this was explained by the expansion of the volume per C60-molecule and the corresponding increase in the density of states at the Fermi level in the intercalated crystals. On closer examination it has, however, turned out to be unlikely that this is the mechanism behind the increase in Tc. An alternative explanation of the enhanced transition temperatures assumes that the conduction electrons not only couple to the vibrational modes of the C60-molecule, but also to the modes of the intercalated molecules. We investigate the possibility of such a coupling. We find that, assuming the ideal bulk structure of the intercalated crystal, both a coupling due to hybridization of the molecular levels, and a coupling via dipole moments should be very small. This suggests that the presence of the gate-oxide in the field-effect-devices strongly affects the structure of the fullerene crystal at the interface.