Shubnikov-de Haas oscillations of the quasi-two-dimensional organic conductor β-(BEDT-TTF)₂i₃ under pressure

We measured the Shubnikov-de Haas oscillations of the quasi-two-dimensional organic conductor β-(BEDT-TTF)₂I₃ under a hydrostatic pressure of 7 kbar. The amplitude of the oscillations was greatly reduced from its ambient pressure value, but the quasi-two-dimensional nature was preserved in spite of a five-fold decrease in T_c. While the fundamental frequency increased by 6.3 %, reflecting the compressibility under pressure, the ratio of the modulation frequency to the fundamental frequency decreased from 9.9 × 10^-3 to 8.3 × 10^-3. Pressure not only compressed the material but also rendered the Fermi surface more two-dimensional.