The origin of the phase separation in partially deuterated   $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br studied by infrared magneto-optical imaging   spectroscopy
  The direct observation of the phase separation between the metallic and insulating states of 75 %-deuterated $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br ($d33$) using infrared magneto-optical imaging spectroscopy is reported, as well as the associated temperature, cooling rate, and magnetic field dependencies of the separation. The distribution of the center of spectral weight ($< \omega >$) of $d33$ did not change under any of the conditions in which data were taken and was wider than that of the non-deuterated material. This result indicates that the inhomogenity of the sample itself is important as part of the origin of the metal - insulator phase separation. 
T. Nishi, S. Kimura, T. Takahashi, T. Ito, H.J. Im, Y.S. Kwon, K.   Miyagawa, H. Taniguchi, A. Kawamoto, K. Kanoda