Magnetic-field-induced superconductivity in layered organic molecular crystals with localized magnetic moments

Abstract

$\ensuremath{\lambda}\ensuremath{-}(\mathrm{BETS}{)}_{2}{\mathrm{FeCl}}_{4}$ undergoes transitions from an antiferromagnetic insulator to a metal and then to a superconductor as a magnetic field is increased. We use a Hubbard-Kondo model to clarify the role of the ${\mathrm{Fe}}^{3+}$ magnetic ions in these phase transitions. In the high-field regime, the magnetic field acting on the electron spins is compensated by the exchange field ${H}_{e}$ due to the magnetic ions. We show how ${H}_{e}$ can be extracted from the observed splitting of the Shubnikov--de Haas frequencies. We predict the field range for field-induced superconductivity in other materials.