The quasi-two-dimensional organic conductor λ-(BETS)2FeCl4 undergoes an antiferromagnetic state under 8.5 K accompanied by a metal-to-insulator transition. Furthermore, superconductivity appears when an external magnetic field of more than 18 T is applied. This was thought to be due to the so-called Jaccarino-Peter compensation mechanism, in which the 3d electrons of iron form a magnetically ordered state in a zero magnetic field, and the internal magnetic field generated by the 3d electrons suppress the superconductivity of the π electrons. However, this does not explain the reason for the insulating state at 8.5 K.
In 1999, zero-resistivity was also observed under the high-pressure above 3 kbar and below 2.3 K by means of resistivity measurements. However, the Meissner effect had not been observed and this zero-resistivity cannot be attributed to superconductivity. In this study, we performed magnetic susceptibility measurements under precisely controlled pressure on this material to investigate the relationship between the metal-insulator transition and superconductivity.
As a result, we could surmise that superconductivity was achieved at 2.8 K for 1.8 kbar and at 2.3 K for 2.640 kbar. Details of our experiments will be presented.