报告摘要：The Eu valence state in compressed EuO has remained controversial since the discovery of its pressure-induced isostructural volume collapse over fifty years ago. The transition was originally attributed to a Eu²⁺→Eu³⁺ valence change driven by 4f-to-5d charge transfer, supported by Eu L₃- edge X-ray absorption measurements. Recent theoretical work, however, suggests that the structural and spectroscopic changes arise instead from pressure-induced electron redistribution among crystal-field-split Eu 5d t₂g and eg states. Here, we present a combined experimental and theoretical study of Eu N₄,₅ multiplet excitations using X-ray Raman scattering to resolve this longstanding issue. The second topic is motivated by the recent discovery of unusually high superconducting transition temperatures in compressed Ti and Sc. Although conventional BCS-based calculations reproduce the observed Tc values, the electronic origin of the pressure-enhanced superconductivity remains unclear. Using density functional theory and Quantum Theory of Atoms in Molecules analysis, we examine the evolution of bonding and electron density in the high-pressure polymorphs. The results show that pressure drives localized 3d electrons into increasingly covalent, multi-band bonding networks, providing insight into the electronic and structural factors underlying enhanced superconductivity.

报告人简介：John S. Tse is a materials scientist. His research integrates first-principles electronic-structure calculations, high-pressure experiments, and synchrotron X-ray spectroscopy to understand the behaviour of materials ranging from ices and gas hydrates to electrides and superconductors. He is a Distinguished Professor at the University of Saskatchewan, a Fellow of the Royal Society of Canada, and was appointed as a Tier I Canada Research Chair in Synchrotron Science upon joining the university. Prior to this, he served for over two decades as a Principal Research Officer and Leader of the Theory and Computation Program at the National Research Council of Canada.

邀请人：靳常青

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