Modulated crystal structure of the atypical charge density wave state of single-crystal Lu2Ir3Si5

The three-dimensional charge density wave (CDW) compound Lu2Ir3Si5 undergoes a first-order CDW phase transition at around 200 K. An atypical CDW state is found, that is characterized by an incommensurate CDW with q=[0.2499(3),0.4843(4),0.2386(2)] at 60 K, and a large orthorhombic-to-triclinic lattice distortion with β=91.945(2). We present the modulated crystal structure of the incommensurate CDW state. Structural analysis shows that the CDW resides on the zigzag chains of iridium atoms along c. The structural distortions are completely similar between nonmagnetic Lu2Ir3Si5 and previously studied isostructural magnetic Er2Ir3Si5 with the small differences explained by the different values of the atomic radii of Lu and Er. Such a similarity is unique to R2Ir3Si5 (R=rareearth). It differs from, for example, the rare-earth CDW compounds R5Ir4Si10 for which Lu5Ir4Si10 and Er5Ir4Si10 possess entirely different CDW states. We argue that the mechanism of CDW formation, thus, is different for R2Ir3Si5 and R5Ir4Si10.