Nanocrystalline thin films with charge density wave ground state

Variable range hopping conductivity in nanocrystalline films of K0.3MoO3

“…At the same temperature, the Raman-active CDW amplitude mode appears in fs-TRS [3,5]. The films with lower resistance and a more pronounced anomaly at 150 K also had better texture, the grains preferably ordered in orthogonal directions, as observed by atomic force microscopy (AFM) [4,5].…”

“…AFM images of the examined films show granular structure [3,5]. Individual grains are elongated, ranging from 50 to 150 nm in width, and 150 to 200 nm in length.…”

“…Standard characterization techniques showed that our films are composed of nanocrystalline grains [3][4][5], while the presence of the CDW in grains below 150 K was unambiguously demonstrated by the observation of CDW amplitude mode in femto-second time resolved spectroscopy (fs-TRS) [3]. In contrast to this, initial transport measurements showed no evidence of the sharp Peierls transition (characteristics of the nominally pure bulk samples) in the temperature dependence of the resistance R(T) of the films, and the data could be fit to a one-dimensional (1d) variable range hopping (VRH) dependence [3].…”

“…The fit to a simple Efros-Shklovskii variable range hopping (ES-VRH) [6] expression for conductivity indicates two temperature ranges with different fitting parameters T 0 and a crossover at 45 K. On the other hand, the logarithmic derivative of R(T) [5] suggests a different VRH expression with a temperature-dependent pre-exponential factor and a crossover to a nearest neighbor hopping activated regime above 100 K. We discuss both types of analysis within the theory of inelastic co-tunneling in granular metals [7] with respect to the ground state in grains and to the morphology of the investigated films.…”