Structural properties and phase transition of hole-orbital-ordered (CHNH)CuCl studied by resonant and non-resonant X-ray scatterings under high pressure

Owada, Kenji; Ishii, Kenji; Inami, Toshiya; Murakami, Yoichi; Shobu, Takahisa*  ; Osumi, Hiroyuki*; Ikeda, Naoshi*; Oishi, Yasuo*

The effects of hydrostatic pressure on a structure and the corresponding resonant X-ray scattering (RXS) spectrum have been investigated for the hole-orbital-ordered compound (CHNH)CuCl. We have found a structural phase transition at Pc=4 GPa. The reduction of the Jahn-Teller distortion (JTD) toward Pc is also ascertained by structural analyses. The gradual change in the color of the crystal is also observed in connection with the structural change near Pc. We experimentally confirmed that the RXS intensity comes from the polarization of the density of states of px and py symmetries, which is mainly dominated not by the on-site 3d-4p Coulomb interaction but by the JTD of the CuCl octahedron. The RXS study under a high pressure shows no striking change as JTD is suppressed by the application of pressure. On the other hand, the RXS intensity becomes zero above Pc. The results indicate that the local environment of the Cu ion markedly changes. Two possible structures above Pc are proposed.