Evidence of band-filling control of τ−type organic conductors by thermal treatment

The two dimensional (2D) organic conductor τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y, (y ≤ 0.875) is known to exhibit sample dependence of the electric resistivity. The present authors assumed that the possible difference in y is responsible for the sample dependence and the amount of y can be effectively controlled for each crystal by thermal treatment. If it is the case, the band filling of the present compound can be also controlled. To observe the change in the band filling directly, the magnetoresistance was measured up to 45 T at 0.5 K for the magnetic field perpendicular to the conducting ab plane of the samples from one single crystal, one of which had been heated up to 400 K. Both the samples showed the two series of Shubnikov-de Haas oscillations of the magnetoresistance as reported previously. We, however, found the remarkable difference in the frequency of the slower oscillations between the virgin and heated samples. The X-ray study revealed that the thermal treatment does not affect the crystal structure related to the 2D band structure. Thus the frequency change by the thermal treatment is caused by the change in the band filling and it is tuned by heating the crystal.