DEPARTMENT OF APPLIED PHYSICS 121 Representative Publications • Phys. Rev. Lett. 129, 168002 (2022) • Phys. Rev. Lett. 125, 265703 (2020) • Phys. Rev. Lett. 125, 258001 (2020) • Phys. Rev. Lett. 124, 095501 (2020) • Science 343, 975 (2014) • Science 328, 1676 (2010) Email c.h.lam@polyu.edu.hk Qualification BSc (The University of Hong Kong) PhD (The University of Michigan) ORCID ID 0000-0002-0476-1857 Dr LAM Chi-hang Associate Professor Research Overview Dr Lam currently focuses on the physics of glass. Many materials are glass formers which can be cooled to a disordered solid state at the glass transition temperature. Examples include window glass, glassy polymers, metallic glasses, etc. Philip Anderson, a Nobel Laureate, wrote in 1995 that “The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition.” At present, not only that is there no encompassing theory of glass agreeable by most researchers, even the most fundamental questions such as whether the glass transition is thermodynamically or kinetically driven are highly controversial. Recently, by performing days-long experiments on glassy colloidal systems, we have shown that fluid-like behaviours diminish at very deep supercooling. Motions are instead dominated by sequences of activated particle hops. We suggest that they are induced by defects called quasivoids, each consisting of a few localised free volume fragments with a combined volume comparable to that of a particle. Their relevance is evidenced by the observation of the reversible conversion of a quasivoid into a vacancy when diffusing across a glass-crystal interface. The dynamics of glass can then be described based on motions of these quasiparticles. An additional feature is that quasivoid motion is not only dictated by the system disorder but it also perturbs the disorder. These mechanisms are incorporated into a distinguishable-particle lattice model (DPLM). It has successfully reproduced a wide range of glassy phenomena, including very non-trivial ones such as Kovacs paradox and diffusion coefficient power-laws under partial-swap. In this picture, glassy dynamics is analytically tractable using a local random configuration-tree theory. Dr Lam is currently further developing and applying these theoretical concepts and techniques to explain various glassy phenomena.
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