Transport property of α-(BEDT-TTF)2I3 under high pressure–ultra narrow gap semiconductor

α-(BEDT-TTF) 2 I 3 under high pressures is characterized by temperature(T) independent conductivity and strongly independent carrier density (It increases by about 10 6 times between 1K and 300K). We investigated the property of carriers (electrons and holes) over the pressure between 11-18kbar. This system is quite a new type of ultra narrow gap (less than 3meV) semiconductor. At low T, both electrons and holes have high mobility(10 6 cm 2 /V.sec) and low density (10 cm -3 ). They have light mass of about 0.03m 0 . This state was found to be very sensitive to the magnetic field.