title: Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors.
abstract: Controlled access to the border of the Mott insulating state by variation of control parameters offers exotic electronic states such as anomalous and possibly high-transition-temperature (Tc) superconductivity. The alkali-doped fullerides show a transition from a Mott insulator to a superconductor for the first time in three-dimensional materials, but the impact of dimensionality and electron correlation on superconducting properties has remained unclear. Here we show that, near the Mott insulating phase, the upper critical field Hc2of the fulleride superconductors reaches values as high as ∼90 T-the highest among cubic crystals. This is accompanied by a crossover from weak- to strong-coupling superconductivity and appears upon entering the metallic state with the dynamical Jahn-Teller effect as the Mott transition is approached. These results suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity with high-Tcand high-Hc2.
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kasahara
authors.affiliation: Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takeuchi
authors.affiliation: Department of Chemistry, Durham University, Durham DH1 3LE, UK.
authors.forename: R H
authors.initials: RH
authors.lastname: Zadik
authors.affiliation: WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Y
authors.identifier: 0000-0002-3493-2194
authors.initials: Y
authors.lastname: Takabayashi
authors.affiliation: Department of Chemistry, Durham University, Durham DH1 3LE, UK.
authors.forename: R H
authors.initials: RH
authors.lastname: Colman
authors.affiliation: NHMFL, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: R D
authors.initials: RD
authors.lastname: McDonald
authors.affiliation: Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Rosseinsky
authors.affiliation: WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.|Japan Science and Technology Agency (JST), ERATO Isobe Degenerate π-Integration Project, Tohoku University, Sendai 980-8577, Japan.
authors.forename: K
authors.identifier: 0000-0003-4524-3084
authors.initials: K
authors.lastname: Prassides
authors.affiliation: Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.|RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Iwasa