The Superstructure of the Organic Superconductor β-(BEDT-TTF)2I3under Pressure

An X-ray diffraction study is made on the incommensurate superstructure in the organic superconductor β-(BEDT-TTF) 2 I 3 under pressure. The onset temperature of the superstructure decreases from 175 K to 150 K with increasing pressure from 1 bar to about 400 bar, above which no superstructure is found. The wave vector specifying the superstructure is found to change in the range between 100 K and ∼120 K. This wave-vector change slows down at low pressures. At ambient pressure it takes more than 30 hr to complete the change. This wave-vector change is found to bring about a new “2 K superconducting state” in the title compound.