Interplay of Charge Density Wave States and Strain at the Surface of CeTe_2

We use scanning tunneling microscopy (STM) to study charge density wave (CDW) states in the rare-earth ditelluride, ${\mathrm{CeTe}}_{2}$. Our STM measurements surprisingly detect a unidirectional CDW with $q\ensuremath{\sim}0.28\phantom{\rule{0.16em}{0ex}}{a}^{*}$, which differs from previous experimental and first-principles studies of the rare-earth ditellurides, and which is very close to what is found in experimental measurements of the related rare-earth tritellurides. Furthermore, in the vicinity of an extended subsurface defect, we find spatially-separated as well as spatially-coexisting unidirectional CDWs at the surface of ${\mathrm{CeTe}}_{2}$. We quantify the nanoscale strain and its variations induced by this defect, and establish a correlation between local lattice strain and the locally-established CDW states; this suggests that lattice strain plays an important role in determining the specific characteristics of the established CDW state. Our measurements probe the fundamental properties of a weakly-bound two-dimensional Te sheet, which experimental and theoretical work has previously established as the fundamental component driving much of the essential physics in both the rare-earth di- and tritelluride compounds.