Pressure-induced phase switching of Shubnikov-de Haas oscillations in the molecular Dirac fermion system α-(BETS)2I3

We report on the Shubnikov-de Haas (SdH) oscillations in the quasi-two-dimensional molecular conductor alpha-(BETS)(2)I-3 [BETS: bis(ethylenedithio)tetraselenafulvalene] laminated on polyimide films at 1.7 K. From the SdH phase factor we verified experimentally that the material is in the Dirac fermion phase under pressure. alpha-(BETS)(2)I-3 is in the vicinity of the phase transition between strongly correlated insulating and Dirac fermion phases, and is a possible candidate for an ambient-pressure molecular Dirac fermion system. However, the SdH oscillations indicate that the Berry phase is zero at ambient pressure. Under pressure, a pi Berry phase emerges when the metal-insulator crossover is almost suppressed at similar to 0.5 GPa. The results contrast with those for the pioneering molecular Dirac fermion system alpha-(BEDT-TTF)(2)I-3 [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] in which Dirac fermions and semiconducting behavior are simultaneously observed.

Automated summary

The study investigates the SdH oscillations in alpha-(BETS)2I-3 molecular conductor at 1.7K, showing that it is in the Dirac fermion phase under pressure. While the material is near the phase transition between strongly correlated insulating and Dirac fermion phases, it is a possible candidate for an ambient-pressure molecular Dirac fermion system. The Berry phase is zero at ambient pressure, but a π Berry phase emerges under pressure, indicating a suppressed metal-insulator crossover at around 0.5 GPa. This contrasts with the behavior of the pioneering molecular Dirac fermion system alpha-(BEDT-TTF)2I-3.