Electron injection into superconducting trivalent fullerides close to the Mott transition boundary
Abstract
To date, superconductivity in fullerides has been almost exclusively tuned by (chemical or physical) pressure control of the conduction bandwidth, W at half filling. This contrasts sharply with the extensive control of the superconducting transition temperature, Tc in atom-based superconductors such as the cuprates and iron pnictides and chalcogenides via changes in valence (bandfilling). Here, we investigate the effect of doping away from the exactly half-filled C3−60 level in quaternary face-centered-cubic (fcc) — structured fulleride solids with nominal composition (Rb2.5−xCsx)Ba0.5C60 (0≤x≤2.5), in which divalent Ba2+ ions partially replace monovalent alkali Rb+/Cs+ ions. The resulting charged-modified fullerides in which the t1u bandwidth is also varied with changing x show a dome-shaped dependence of Tc on interfullerene separation in analogy with their half-filled antecedents. However, following electron injection beyond half-filling, the superconductivity dome is found to shift towards shorter interfullerene separations, i.e. towards increased conduction bandwidths.
