Charge-Density Wave Localization and Co-Existence in 1T-TaS2
Microscopy and Microanalysis
Several strongly electron-correlated materials are known to display charge-density waves (CDWs) under various conditions (e.g., low temperatures) . In 1T-TaS2, for example, three distinct CDW phases of differing levels of commensurability are known to exist, the nature of each having been shown to depend on temperature. Above 350 K, an incommensurate phase is present, which is a semi-metallic state consisting of a randomly-oriented lattice distortion [2,3]. Below 350 K, this phase is thought
... to transform into a nearly commensurate (NCCDW) phase, which further transforms into a commensurate (CCDW) phase below 180 K. The NCCDW and CCDW phases consist of 6 and 12 Ta atoms, respectively, displaced toward a single central atom. In reciprocal space, the NCCDW phase is identified by the presence of an array of hexagonal satellite spots midway between each Bragg spot. The CCDW phase appears as a smaller hexagon of satellite spots surrounding each Bragg spot, which represents a repeating array of "Star of David" configurations  . Further, the satellite spots associated with each phase occur at distinct scattering angles. Conversely, in the relatively high-temperature semimetallic phase, only Bragg spots are observed, which arise from an undistorted hexagonal lattice. Dynamics manifesting as changes in features of the satellite spots for both the NCCDW and CCDW phases have been studied using dedicated femtosecond X-ray and electron diffraction techniques, with scattering signal accumulated from relatively large specimen regions [4, 5] . However, the behavior of localized CDW phases within discrete micrometer to nanoscale regions remains poorly understood.