Quantum oscillation measurements on the organic superconductor ?-(BEDT-TTF)2I3

Quantum oscillation experiments were performed on high quality single crystals of ?-(BEDT-TTF)2I3. Their electronic properties are similar to those of crystals of ?-(BEDT-TTF)2(I3)1-x(AuI2)x (x < 0.02). Nevertheless, in the neat crystals used here, quantum oscillations for the a-orbit (Fa?= 780 T) are observed already at a field of 2 T, and the magnetic breakdown of the a-orbit (Fa= 4200 T) occurs at 3 T. In the large magnetic field range, in which quantum oscillations are observed, the warping of the Fermi surface of the a-orbit and a-orbit could be determined to be aFa?= 6.6 T and aFa?= 16.6 T, respectively. At high magnetic fields, the de Haas-van Alphen signal consists of pronounced inverse saw-tooth oscillations, and the Shubnikov-de Haas signal has a peaked structure. This behaviour is interpreted in terms of magnetic interaction.