Domain control by adjusting anisotropic stress in pyrochlore oxide Cd₂Re₂O₇

The 5d pyrochlore oxide Cd₂Re₂O₇ exhibits successive phase transitions from a cubic pyrochlore structure (phase I) to a tetragonal structure without inversion symmetry below T_s1 of ∼200 K (phase II) and further to another noncentrosymmetric tetragonal structure below T_s2 of ∼120 K (phase III). The two low-temperature phases may be characterized by odd-parity multipolar orders induced by the Fermi liquid instability of the spin-orbit-coupled metal. To control the tetragonal domains generated by the transitions and to obtain a single-domain crystal for the measurements of anisotropic properties, we prepared single crystals with the (001) surface and applied biaxial and uniaxial stresses along the plane. Polarizing optical microscopy observations revealed that inducing a small strain of approximately 0.05% could flip the twin domains ferroelastically in a reversible fashion at low temperatures, which evidences that the tetragonal deformation switches at T_s2 between c > a for phase II and c < a for phase III. Resistivity measurements using single-domain crystals under uniaxial stress showed that the anisotropy was maximum at around T_s2 and turned over across T_s2: resistivity along the c axis is larger (smaller) than that along the a axis by ∼25% for phase II (III) at around T_s2. These large anisotropies probably originate from spin-dependent scattering in the spin-split Fermi surfaces of the cluster electric toroidal quadrupolar phases of Cd₂Re₂O₇.