Singularities at load-induced moiré locking transitions in twist grain boundaries

Recent simulation work on the moiré formed by small angle crystalline twist grain boundaries (TGBs) revealed an unexpected load-induced first-order structural transition. Most likely universal, this unconventional transition drives a frictionally superlubric-to-locked transformation. It involves moiré reconstruction, with emergence of locally commensurate mini-domains, the formation of which implies broader consequences for interfacial phenomena beyond friction, which we study by nonequilibrium molecular dynamics simulations and nonequilibrium Green's function transport calculations. We show that, for small angle ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>θ</a:mi> <a:mo>≲</a:mo> <a:msup> <a:mn>4</a:mn> <a:mo>∘</a:mo> </a:msup> </a:mrow> </a:math> ) Au(111) TGBs at the critical load of a few gigapascals, the transition is accompanied by singular responses, including a sharp dip in mechanical compliance and a <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mo>≈</b:mo> <b:mn>20</b:mn> <b:mo>–</b:mo> <b:mn>30</b:mn> <b:mo>%</b:mo> </b:mrow> </b:math> increase of ballistic electrical resistance as well as of interfacial thermal resistance of mixed phononic and electronic origin. Both reflect the reconstruction of interlayer registry and coupling induced by the emergence of mini-domains. These structurally driven singularities provide experimentally accessible fingerprints of the transition and reveal a unified coupling between mechanical, dissipative, and transport responses at TGBs, opening alternative routes toward the active control of moiré interfacial functionalities.