Domain Control by Adjusting Anisotropic Stress in Pyrochlore Oxide Cd2Re2O7

TL;DR

This study demonstrates how applying anisotropic stress to Cd2Re2O7 can control its domain structure and induce significant anisotropic electronic properties related to its phase transitions and multipolar orders.

Contribution

It reveals that small strains can reversibly flip twin domains and significantly alter resistivity anisotropy in Cd2Re2O7, advancing understanding of strain control in spin-orbit coupled materials.

Findings

Small strain (~0.05%) can reversibly flip twin domains.

Resistivity anisotropy reaches ~25% near Ts2.

Anisotropic properties are linked to spin-dependent scattering.

Abstract

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.