The observation of changes in the crystal structure at low temperatures plays very important roles in gaining a better understanding of mechanism of the phase transformation and stability of the phase as a ground state. For these purposes, two sets of 3He-4He dilution refrigerators with a top loading facility were installed at BL-3C2 and 6C1 of the Photon Factory. The former is used exclusively for taking topographs from quantum crystals of solid 3He and 4He for studies of lattice defects. Typical examples of topographs, which indicate an annealing effect of solid helium which might be understood from a viewpoint of a quantum tunneling effect, are presented. The latter refrigerator is used for studies of crystalline solids by x-ray diffraction. A splitting of the Laue spots of Cs2NaHoCl6 below 150 mK, giving evidence of a Jahn-Teller transition of the first kind, which is the lowest transition temperature ever detected, was observed as a new peculiarity of the phase transition at ultralow temperature.
ASJC Scopus subject areas