Electron correlation and two dimensionality in the spin-density-wave phase of (TMTTF)${}_2$Br under pressure

Abstract

The incommensurate spin-density-wave (SDW) phase in (TMTTF)${}_2$Br was investigated through transport measurements under pressure and magnetic fields parallel to the $c^{\ast }$ axis. For the incommensurate SDW phase of (TMTTF)${}_2$Br stabilized above 0.5 GPa, the SDW transition temperature $T_{\mathrm{SDW}}$ increases with the applied magnetic field. The field dependence of $T_{\mathrm{SDW}}$ is described by a quadratic behavior and the coefficient of the quadratic term increases with increasing pressure. These results are consistent with the prediction of the mean-field theory based on the suppression of the SDW transition by two-dimensionality. From the relation between the coefficient of the quadratic term and $T_{\mathrm{SDW}}$ at zero magnetic field, we determined the role of electron correlation and two dimensionality in the SDW phase of (TMTTF)${}_2$Br under pressure and found that the SDW transition in (TMTTF)${}_2$Br can be well explained within the mean field theory by taking into account the reduction of the coupling constant $N(0)I$ by pressure.

5 pages, 5 figures