12/18
2023
Seminar
- Title题目 复相图与超临界物质 (Complex Phase Diagram and Supercritical Matter)
- Speaker报告人 欧阳霄宇（北京大学）
- Date日期 2023年12月18日 10：00-12:00
- Venue地点 南楼6420
Abstract摘要
The supercritical region is often described as uniform with no definite transitions. The distinct behaviors of the matter therein (as liquid-like and gas-like), however, suggest “supercritical boundaries”. Here, we provide a mathematical description of these phenomena by revisiting the Lee-Yang (LY) theory and introducing a complex phase diagram, i.e. a 4-D one with complex T and p. While the traditional 2-D phase diagram with real T and p values (the physical plane) lacks LY zeros beyond the critical point, preventing the occurrence of criticality, the off-plane zeros in this 4-D scenario possess critical anomalies in various physical properties. For example, when the isobaric heat capacity Cp, which is a response function of the system to T, is used to separate the supercritical region, this 4D complex phase diagram can be visualized by reducing to a 3D one with complex T and real p. Then, we find that the supercritical boundary defined by C_p shows perfect correspondence with the projection of the edges of the LY zeros with complex T in this 3D phase diagram on the physical plane, whilst in conventional LY theory these off-plane zeros are neglected. The same relation applies to the isothermal compression coefficient K_T which is a response function of the system to p, where complex p should be used. This correlation between the Widom line and the edges of LY zeros is demonstrated in three systems, i.e., van der Waals model, 2D Ising model and water, which unambiguously reveals the incipient phase transition nature of the supercritical matter. With this extension of the LY theory and the associated new findings, a unified picture of phase and phase transition valid for both the phase transition and supercritical regions is provided, which should apply to the complex phase diagram of other thermodynamic state functions. (Ref: arXiv:2303.16784).
邀请人：
金瑜亮 研究员
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