Transport properties of organic conductor α-(BEDT-TTF)2I3 and θ-(BEDT-TTF)2I3 under hydrostatic pressure or uniaxial strain

Pressure controlled switching between a metallic state and a semiconducting state was successfully realised on organic conductors α-(BEDT-TTF)2I3 and θ-(BEDT-TTF)2I3. Under high hydrostatic pressures, α-(BEDT-TTF)2I3 behaves as an ultra-narrow gap (about 1 meV at p=18 kbar) semiconductor. It is characterised by strongly temperature(T)-dependent carrier density. It decreases by about 106 times between 300 and 1 K. When strained in b-axis, on the other hand, this material was found to behave as a quasi-two-dimensional (Q2D) metal with a large Fermi surface. The carrier density is independent of T while conductivity increases by about 102 times between 300 and 4 K. θ-(BEDT-TTF)2I3 exhibits a similar change. Under the ambient pressure, it is a typical Q2D metal and changes to a narrow gap semiconductor under pressures above about 5 kbar.