Rotation of Unidirectional Charge Density Wave in ErTe3 in Response to Antisymmetric Strain Revealed by X-ray Diffraction

We observed via x-ray diffraction (XRD) that application of anisotropic strain to an ErTe₃ crystal can rotate the primary in-plane (here, the a/c plane) charge density wave (CDW) wavevector by 90^o. ErTe₃ belongs to the rare-earth tritelluride family, RTe₃ (R=La-Pr, Sm, Gd-Tm), which are quasi-2D materials comprising nearly-square Te nets that exhibit unidirectional incommensurate CDW states. These materials are a model system to explore open questions regarding CDW formation and its interrelation with superconductivity.

Although RTe₃ is weakly orthorhombic and the primary CDW forms along the c-axis, Kohn anomalies are nevertheless observed at equivalent wavevectors in both in-plane directions, suggesting the material is ‘almost tetragonal’. Here, we demonstrate that the direction of the primary CDW can in fact be switched from the c to a-axis by applying anisotropic in-plane strain. We also performed complementary transport measurements that corroborate the XRD results. Additionally, our measurements reveal evidence for a domain structure at intermediate strain values. Present verification of the ability to strain tune the CDW orientation in this material makes it an ideal candidate to host a possible vestigial nematic phase.