X-ray Diffraction Measurement Below 1 K

The Jahn-Teller distortion of TmVO4 with T c =2.15 K was measured by an x-ray diffractometer between 0.22 and 3.5 K. A powder specimen of TmVO4 was cooled by a 3He-4He dilution refrigerator mounted on the goniometer. Unexpected different intensities of the 400 and 040 lines in the orthorhombic phase were observed. To the authorsʹʹ knowledge this is the first x-ray diffraction measurement below 1K by a counter method for a powder specimen.