Relation between disorder and homogeneity in an amorphous metal

Abstract

Disorder and homogeneity are two concepts that refer to spatial variation of the system potential. In condensed-matter systems disorder is typically divided into two types; those with local parameters varying from site to site (diagonal disorder) and those characterized by random transfer-integral values (off-diagonal disorder). Amorphous systems in particular exhibit off-diagonal disorder due to random positions of their constituents. In real systems diagonal and off-diagonal disorder may be interconnected. The formal depiction of disorder as local deviations from a common value focuses attention on the short-range components of the potential-landscape. However, long range potential fluctuation are quite common in real systems. In this work we seek to find a correlation between disorder and homogeneity using amorphous indium-oxide films with different carrier-concentrations and with different degree of disorder. Thermal treatment is used as a means of fine tuning the system disorder. In this process the resistance of the sample decreases while its amorphous structure and chemical composition is preserved. The reduced resistivity affects the Ioffe-Regel parameter that is taken as a relative measure of disorder in a given sample. The homogeneity of the system was monitored using inelastic light-scattering. This is based on collecting the Raman signal from micron-size spots across the sample. The statistics of these low-energy data are compared with the sample disorder independently estimated from transport measurements. The analysis establishes that heterogeneity and disorder are correlated.