Hidden structure in amorphous solids

Review copy ± not for distribution (pss-logo will be inserted here by the publisher) pss-­‐Header will be provided by the publisher 1 Introduction The continuous random network (CRN) has become the accepted model for homogeneously disordered materials, and for good reason: such atomistic models reproduce the experimentally observed properties of the materials, including some of the finer details, such as the Urbach tailing in the electronic density of states[1][2][3][4]. Recently [5], we have closely examined some particularly realistic CRN models of amorphous silicon (a-Si), and reported that there are subtle correlations that have not been previously noted: short bonds tend to be connected to other short bonds and an analogous statement for long bonds. In a-Si, the longer bonds form filamentary (1-D) structures, and the short bonds tend to cluster in a higher dimensional way, albeit with some 1-D character. We have shown that the Urbach tails in the electronic density of states arise from these structures [4](the valence tail associated with the short bonds, conduction tail with long bonds).