Saif Siddique1,James Hart1,Ratnadwip Singha2,Myung-Geun Han3,Michael Colletta1,Noah Schnitzer1,Lena Kourkoutis1,Yimei Zhu3,Leslie Schoop2,Judy Cha1
Cornell University1,Princeton University2,Brookhaven National Laboratory3
Saif Siddique1,James Hart1,Ratnadwip Singha2,Myung-Geun Han3,Michael Colletta1,Noah Schnitzer1,Lena Kourkoutis1,Yimei Zhu3,Leslie Schoop2,Judy Cha1
Cornell University1,Princeton University2,Brookhaven National Laboratory3
Rare-earth tritellurides (RTe<sub>3</sub>; R = rare-earth elements) are a family of layered compounds exhibiting charge density wave (CDW) order. They have rich phase diagrams involving other quantum phases, such as superconductivity and magnetism, providing an opportunity to understand the interplay between these phases by studying the mechanisms influencing the phase transitions. RTe<sub>3</sub> with lighter rare-earth elements (La-Gd) has a unidirectional CDW, while the ground state for the heavier rare-earths (Tb-Tm) has a second CDW at a lower temperature, and is orthogonal to the first with slighly larger wavevector, creating a bidirectional CDW. The direction of the charge and lattice modulations in the CDW state is governed by the orthorhombicity of the crystal structure. The in-plane axes in these materials are nearly equal, but the presence of a glide plane only along one of the axes makes the unit cell orthorhombic, and the higher temperature CDW (for lighter RTe<sub>3</sub>, the only CDW) emerges along this direction.<br/>In this study, we use <i>in-situ </i>cryogenic scanning transmission electron microscopy (STEM) techniques to understand the influence of structural defects on the orthorhombicity and the CDW order in exfoliated flakes of LaTe<sub>3</sub>, GdTe<sub>3 </sub>and ErTe<sub>3</sub>: two unidirectional and one bidirectional CDW system. Atomic-resolution STEM images in cross-section reveal the layer stacking in these materials to be disordered, with the disorder density increasing for heavier rare-earths in RTe<sub>3</sub>. These layer stacking defects lead to the presence of glide planes along both in-plane directions rather than along only one in-plane direction, and hence the material loses orthorhombicity. Temperature dependent electron diffraction and 4D-STEM, down to 15 K and 120 K, respectively, are used to study the CDW phase transition behavior of these flakes that reveal the existence of in-plane domain walls. We observe that the loss of orthorhombicity and the presence of domain walls significantly affect the CDW order in these exfoliated flakes of RTe<sub>3.</sub> Our results demonstrate the correlation of stacking defects and domain boundaries with the properties and dynamics of CDW phase transition.