Evolution of order in an amorphous material

A thermal treatment protocol is used to modify the resistance of amorphous GeSbTe compound $(a\text{\ensuremath{-}}\mathrm{GST})$ films. Using consecutive cycles of heating and relaxation, the room temperature resistance of these vacuum-deposited films may be reduced by orders of magnitude while still maintaining their amorphous structure. The main mechanism responsible for the resistance reduction is densification. The modified structure of the $a\text{\ensuremath{-}}\mathrm{GST}$ during heat treatment is manifested through the time-dependent resistance $R(t)$ that is monitored concurrently with the sample temperature. The exponential sensitivity of the resistance of these highly disordered systems allows detection of small changes in disorder. These changes can be correlated with modifications observed in electron diffraction experiments. Systematic study of the $R(t)$ plots generated during heat treatment exposes an auxiliary mechanism that presumably reflects correlations in the system other than nearest-neighbor interactions. The characteristic features of this mechanism, revealed through resistance measurements, herald the appearance of a new element of order in this amorphous compound that has not been detected by conventional structural tools. This illustrates the potential of using transport as a tool for studying fundamental aspects of disorder in glasses.