Hexatic phase in covalent two-dimensional silver iodide.

Bui, Thuy An; Lamprecht, David; Madsen, Jacob; Kurpas, Marcin; Kotrusz, Peter; Markevich, Alexander; Mangler, Clemens; Kotakoski, Jani et al. · Science · 2025

basic_science · Level V

Where this comes from

Abstract

According to the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory, the transition from a solid to liquid in two dimensions proceeds through an orientationally ordered liquid-like hexatic phase. However, alternative mixed melting scenarios, in which melting proceeds through the hexatic phase with both continuous and discontinuous transitions, have also been observed in some two-dimensional systems. In this study, we imaged silver iodide embedded in multilayer graphene using time- and temperature-resolved in situ atomic-resolution scanning transmission electron microscopy and nanobeam electron diffraction. We observed the hexatic phase and provide evidence supporting a mixed melting scenario.