Pressure-induced phase switching of the Shubnikov de Haas oscillations in molecular Dirac fermion system $\alpha-$(BETS)$_{2}$I$_{3}$

TL;DR

This study investigates pressure-induced changes in Shubnikov de Haas oscillations in a molecular Dirac fermion system, revealing a transition from zero to π Berry phase near 0.5 GPa, indicating a phase switch.

Contribution

It provides experimental evidence of pressure-driven phase switching in the Berry phase of a molecular Dirac fermion system, highlighting the tunability of topological properties.

Findings

Berry phase is zero at ambient pressure.

A π Berry phase appears near 0.5 GPa.

Pressure suppresses the metal-insulator crossover.

Abstract

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 $\sim$0.5 GPa. The results contrast 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.