Analysis of possible field - induced superconducti - vity in anthracene , other polyacenes , and C 60

Analysis of possible field-induced superconducti-vity in anthracene, other polyacenes, and C 60 We consider electronic structure and superconductivity aspects in field-doped polyacenes (PA) and C 60. Within a modified Thomas-Fermi approach for typical experimental values of the surface charge density the injected charge is confined to a monolayer. The electron-phonon coupling constant for internal modes λ int is estimated using the work of Devos et al. (Phys. Rev. B 58, 8236 (1998)) and the density of states estimated from a 2D-one-band model derived from a full potential LDA band structure calculation for bulk anthracene. The large differences in the reported T c-values for PA and C 60 are ascribed to enhanced empirical Coulomb pseudopotentials µ * for PA. Recently field-induced superconductivity (FISC) has been reported for field effect transistors (FET) based on various organic systems. 1,2,3 Unfortunately , its very existence and the possibility to produce the necessary extremly high electric fields in FETs have not been verified so far by other groups. 4 Anyhow, an electron-phonon (el-ph) mechanism is considered to be a likely candidate 1,2 , although, details of the FISC are still unknown. Due to the closely related physics of bulk electron n-doped A 3 C 60 (A=K, Rb) the main contributions from high-frequency internal molecular optical phonons ¯ hω ph ∼ 100 meV could be expected. 5 There is a sizable corresponding el-ph coupling in aromatic molecules in general. 6 Its strength increases with decreasing number of π-electrons N π , in line with the T c values (2, 2.7, and 4 K) reported for n-doped penta-, tetra-, and anthracene, respectively). Anyhow , with respect to PA the reason for the much higher T c ≈ 11 (18-26) K, 52 (80-114) K for n-and h-doped C 60 , respectively, (values in brackets for