Public Research Seminar by Advanced Materials Thrust, Function Hub - Modeling polarons in crystalline solids and 2D materials
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The polaron is a quasiparticle formed by collectively dressing an electron with a phonon cloud. It emerges in a crystal lattice when an excess electron is trapped at the lattice distortion induced by itself. In the first part of the talk, I will introduce a novel ab initio theory to study lattice polarons in crystalline solids without resorting to direct density-functional theory (DFT) calculations using supercells. I will describe the mechanisms of polaron formation in wide-gap insulators, using both LiF and Li2O2 as prototypical examples. We analyze the binding energy in terms of the underlying band structure and phonon dispersions, and I will compare our findings with previous calculations and classic models of self-trapped polarons. In the second part of the talk, I will describe the technical difficulties of modelling polarons in 2D materials using DFT and previous methods, along with new methodological developments to fully address this limitation. To illustrate the state-of-the-art method, I will report on recent work on the influence of dimensionality effects on the polaron properties in both bulk and 2D hexagonal boron nitrides (h-BN). The spatial extent of the hole polaron in both cases will be analyzed. We find that the hole polaron is localised within a layer with the width of an atomic orbital (~1.4 Å), i.e. nine times smaller than the one localised in the bulk h-BN, which provides a first vision for the existence of two-dimensional polarons at the atomic scale of 2D materials. Lastly, I will present an analytically solvable model to validate and explain what we have seen predicted by our new methodology, the discovery of a critical condition for the existence of polarons in 2D materials, and I will highlight the key materials properties that blueprint the polaron physics in two dimensions. I will also discuss open questions and possible developments in this field.
Dr. Sio, Weng Hong (Denny), held a Lecturer position (entitled UM Macau Fellow) at the University of Macau, supported by an independent research fellowship. Dr. Sio originally born in Macau, pursued higher education in the United Kingdom after high school. He earned a BSc in Physics with Theoretical Physics at Imperial College London, UK. Subsequently, he pursed his research doctoral studies with Prof. Feliciano Giustino at the University of Oxford, UK, successfully obtained his DPhil in 2020. Dr. Sio received recognition for his academic achievements, being awarded the Bolsa de Mérito Especial (special scholarship of Macao foundation), Macao postgraduate scholarship and the UK EPSRC research studentship. His expertise lies in electronic structure theory, computational physics and high-performance computing. During his doctoral studies, Dr. Sio developed a state-of the-art computational method that facilitates calculations of polarons in materials without relying on supercells. This innovative method has been integrated into the open-source software project EPW. His research interests involve developing new computational methods to explore quasiparticles excitations in condensed matter and quantum materials, electron-phonon interactions, prediction of materials properties and materials informatics etc. He has authored research articles in Nature Physics, Physical Review Letters, Physical Review B and NPJ Computational Materials etc. He is also a regular journal reviewer for Physical Review Letters, Physical Review B and Physical Review Materials.