Shape anisotropy controls 2D melting pathway

YD Fomin and AV Mikheyenkov and EN Tsiok and VN Ryzhov, JOURNAL OF CHEMICAL PHYSICS, 163, 224503 (2025).

DOI: 10.1063/5.0299651

The melting of two-dimensional systems is a fundamental challenge in condensed matter physics, where topological defects and thermal fluctuations play a key role. This work uses molecular dynamics simulations to investigate the melting of particles interacting via the Gay-Berne potential in the weak anisotropy regime (1.0 <= k <= 1.2). We demonstrate that the melting mechanism depends critically on the particle aspect ratio. For weak anisotropy (k < 1.15), the system follows a hybrid Bernard-Krauth scenario, featuring a continuous crystal-to-hexatic transition, followed by a first-order hexatic-to- isotropic liquid transition. At k >= 1.15, the system switches to the full Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young scenario with two continuous Berezinskii-Kosterlitz-Thouless transitions. Introducing binary mixtures of particles with different anisotropies suppresses the first-order transition, stabilizing the continuous melting pathway. Therefore, weak shape anisotropy serves as a fundamental switching parameter governing the universal melting behavior of two-dimensional systems.

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