Dielectric constant in the incommensurate SDW phase of (TMTTF)2Br

The low-frequency dielectric constant was measured in the pressure induced incommensurate SDW phase of (TMTTF)2Br in order to investigate the dynamics of the SDW. Under the pressure above 0.5 GPa, the huge dielectric constant attributed to the motion of the SDW were observed. The temperature dependence of the real part of the dielectric constant ε' whose amplitudes grow with decreasing frequency shows the peak behavior in the incommensurate SDW phase. In contrast of the case of (TMTSF)2PF6, the peak temperature of ε' is constant, irrespective of the frequency. These peak temperature TP are scaled as TP/TSDW∼0.3 irrespective of pressure for the pressure larger than 0.8 GPa and is associated with the sub-phase transition in the incommensurate SDW proposed by the NMR measurement. The dielectric properties are probably connected with the co-existence of the CDW component proposed for high temperature sub-phase.