The origin of the phase separation in partially deuterated κ-(ET)2Cu[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 κ-(ET)2Cu[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 (〈ω〉) 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.