The effect of pressure on the phase diagram of the magnetic field-induced superconducting state of $\lambda $-(BETS)2FeCl4

We report the effect of a small hydrostatic pressure p$\cong $1.4 kBar on the temperature-magnetic field phase diagram of the organic conductor $\lambda $-(BETS)2FeCl4. At zero field a first-order superconducting ($T_{C} \cong $5.6 K) to antiferromagnetic insulator transition ($T_{N} \cong $4 K) is observed. The close proximity between both phases is suggestive of an unconventional superconducting pairing mechanism. Furthermore, the transition temperature towards the field-induced superconducting state (FISC), as well as its concomitant upper critical field, is found to increase by a factor of ∼33 %. The phase diagram of the FISC state for both $p = 1$Bar and 1.4 kBar are well described in terms of the Jaccarino-Peter effect if the quasiparticle nature of the charge carriers is taken into account. Key words. Organic conductors – magnetism – superconductivity.