  The 5d pyrochlore oxide Cd2Re2O7 exhibits successive phase transitions from a
cubic pyrochlore structure (phase I) to a tetragonal structure without
inversion symmetry below Ts1 of ~200 K (phase II) and further to another
noncentrosymmetric tetragonal structure below Ts2 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 (0 0 1) 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 Ts2 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 Ts2 and turned over across Ts2: resistivity along the c axis
is larger (smaller) than that along the a axis by ~25% for phase II (III) at
around Ts2. These large anisotropies probably originate from spin-dependent
scattering in the spin-split Fermi surfaces of the cluster electric toroidal
quadrupolar phases of Cd2Re2O7.
