X-ray backscattering study of crystal lattice distortion in hidden order of URuSi

Tabata, Chihiro*; Inami, Toshiya; Michimura, Shinji*; Yokoyama, Makoto*; Hidaka, Hiroyuki*; Yanagisawa, Tatsuya*; Amitsuka, Hiroshi*

We performed synchrotron X-ray diffraction measurements on a small single crystal of URuSi. A backscattering diffraction setup (2) in combination with a Si(6 6 0) monochromator ensures a high instrumental resolution of , where denotes a lattice-plane spacing and is its spread expressed as the full width at half maximum (FWHM). We carefully measured the (5 5 0) Bragg peak in the temperature range between 5 and 25 K, and found it to show no signature of broadening and splitting when "Hidden Order (HO)" sets in below 17.5 K. Temperature variation of the peak position closely follows the behaviour of the known linear thermal expansion coefficient. Detailed analysis of the peak width reveals that the tetragonal fourfold rotational symmetry of URuSi is conserved in HO within the experimental accuracy of the orthorhombicity of .