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Abstract
We performed synchrotron X-ray diffraction measurements on a small single crystal of with approximate dimensions of
. A backscattering diffraction set-up (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
is conserved in HO within the experimental accuracy of the orthorhombicity of
. We also found that the (5 5 0) peak profile exhibits a temperature-independent fine structure, which indicates that the tetragonal
-axis lattice parameter of the used crystal is distributed with a FWHM of
.
Acknowledgements
We are grateful to H. Kusunose and H. Harima for useful discussions, and R. Kumai, H. Nakao and K. Kobayashi for their helpful suggestions and experimental support at KEK. We warmly thank P.M. Oppeneer, P.S. Riseborough and J.A. Mydosh for encouragements and fruitful discussions.
Notes
This work was partly supported by Grant-in-Aid for Exploratory Research [grant number 25610100], Scientific Research (c) [grant number 25400346], and The Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation from Japan Society for the Promotion of Science.