Jin Wang
(ICTP)
 

Moiré interfaces, formed by twisting or lattice mismatch between crystalline surfaces, provide a unique platform where structural degrees of freedom are significantly amplified. While their electronic properties have been extensively explored, the role of structural transitions and their impact on mechanical and non-equilibrium behaviors remain less understood.
A systematic atomistic framework is presented to classify and understand three types of structural phase transitions in moiré systems, each governed by a distinct degree of freedom. These transitions are investigated using a combination of large-scale molecular dynamics and quasi-static simulations based on empirical potentials, complemented by density functional theory, non-equilibrium transport calculations, and Landau-type mean-field theories, enabling a consistent description across multiple scales.
First, releasing the normal degree of freedom--typically frozen by substrate support--leads freestanding 2D material bilayers to undergo a universal moiré buckling transition [1-2]. The transition and its spatial periodicity are driven by intrinsic stress fields within the moiré superlattice, resulting in a variety of emergent mechanical and electronic responses. Second, an Aubry-type transition emerges among incommensurate 2D bilayers [3], leading to pinning and marking the breakdown of superlubric sliding [4]. Here too we establish a unified phase diagram in terms of twist angle, in-plane elasticity, and interfacial interactions. Third, a distinct load-induced Aubry-type transition arises in twisted grain boundaries of 3D metals such as gold [5-6], where it produces first-order locking, accompanied by abrupt changes in friction, thermal transport, and electronic conduction.
These results exemplify a unified picture in which structural degrees of freedom serve as key control parameters linking interfacial structure, dissipation, and transport, also interesting for designing low-dissipation and reconfigurable nanoscale systems.
 
[1] Jin Wang, and Erio Tosatti. Universal Moiré Buckling of Freestanding 2D Bilayers. PNAS 121, e2418390121 (2024).
[2] Jin Wang, et al., Bending Stiffness Collapse, Buckling, Topological Bands of Freestanding Twisted Bilayer Graphene. Phys. Rev. B 108, L081407 (2023).
[3] Jin Wang, and Erio Tosatti. Aubry Pinning Transition of Twisted Two-Dimensional Material Bilayers. Phys. Rev. B 112, 155406 (2025).
[4] Jin Wang, Ali Khosravi, Andrea Vanossi and Erio Tosatti. Colloquium: Sliding and pinning in structurally lubric 2D material interfaces, Rev. Mod. Phys. 96, 01100214 (2024).
 

Zoom registration link:
https://zoom.us/meeting/register/j8uF4BHvS4mlGY467fB5Iw