The effect of disorder on phases across two-dimensional thermal melting

The study of two-dimensional (2D) melting has drawn significant research interest over a long time because of its defect-mediated description given by KTHNY theory, which yields an exotic hexatic phase sandwiched between the solid and liquid. This is quite unlike their 3D counterparts undergoing a first-order direct melting between solid and liquid. While there had been significant research on KTHNY-physics in microscopic models of classical systems, careful studies of the role of disorder on the different phases and the phase transitions have yet to be explored significantly in the literature. In this talk, I will present results from our systematic study of a two-dimensional system of classical particles with Gaussian-core interactions in disordered environments. The pure system validates the conventional two-step melting with a hexatic phase intervening between the solid and the liquid. This picture is modified in the presence of pinning impurities. A random distribution of pinning centers forces a hexatic-like low-temperature phase that transits into a liquid at a single melting temperature. In contrast, pinning centers located at randomly chosen sites of a perfect crystal anchor a solid at low temperatures, which undergoes a direct transition to the liquid, destabilizing the hexatic phase, like in the case of three dimensions. Thus, the two-step melting is lost in either case of disorder. I will also discuss about the dependency of the characteristics of melting on the nature of the impurities.