Observation of long-range anisotropy in a vapor-deposited metallic glass

The mesoscopic structure of amorphous materials remains to be understood. Although amorphous systems are often thought to be randomly structured beyond short-range ordering, a number of studies reveal the importance of medium-range ordering up to a few nanometers. Here, using a newly available high-flux nanofocused X-ray beam, we observe anisotropy in a vapor-deposited PdCuSi metallic glass even in a large probed volume of around 60 nm x 60 nm x 5 mu m. With annealing, the anisotropy disappears without crystallization. The observations allow us to exclude alternative explanations including geometric and strain effects, leading to the conclusion that the anisotropy must arise from structural correlations. Our results suggest that anisotropy may persist even to macroscopic scales in amorphous materials, pointing out the need for structural descriptions of glasses beyond isotropic pair correlation functions as well as the possibility to realize glassy structures with long-range correlations.