The influence of Gaussian pinning on the melting scenario of a two-dimensional soft-disk system: First-order versus continuous transition

Two-dimensional systems are realized experimentally as thin layers on a substrate. The substrate can have some imperfections (defects of the crystalline structure, chemical impurities, etc.) with strong interactions with particles within and near the defects. Such randomly distributed centers of strong interactions are called ”pinning centers”. The presence of random pinning can substantially change the behavior of the system. It not only shifts the melting point of the system, but can also change the melting scenario itself. In the present paper the influence of Gaussian pinning on the melting scenario of a two-dimensional system of soft disks is studied by means of molecular dynamics simulation. We randomly introduce into the system of soft disks a set of “pinning centers” which attract the particles via the Gauss potential. We observe that increasing the depth of a Gaussian well leads to a change in the melting scenario of the system: from melting occurring via a first-order liquid-hexatic transition followed by a continuous hexatic-crystal transition to two continuous transitions through an intermediate hexatic phase. We show that there are still two transition stages for strong disorder, but the melting scenario is qualitatively different from that for weak disorder. The results demonstrate that the simple kind of quenched disorder can significantly affect the melting scenario of two-dimensional systems and offer the possibility of their application for the interpretation of complex experiments.