报告人：徐宁（ 中国科学技术大学）

报告时间：2020年5月25日下午14:00-15:00

腾讯会议ID：328306615

报告摘要：

Soft-core particles interacting via Spring-like repulsion exhibit multiple reentrant crystallizations with various solid structures. In this talk, we will present our recent observations of the novel two-dimensional melting scenario due to the reentrance and surprising finding of quasicrystals.

According to the KTHNY theory, the melting of a two-dimensional solid is a two-stage process. There exists an intermediate phase called hexatic phase between solid and liquid. Transitions from solid to hexatic and from hexatic to liquid are both continuous. Recently, it has been reported that the hexatic-liquid transition of hard particles is discontinuous and the transition can evolve from discontinuous to continuous when the softness of particles is tuned. For soft-core particle systems which reach the first maximum melting temperature  at a crossover density , we find that  acts as a transition point. Hexatic-liquid transition at  exhibits strong first order transition features. There is a density interval in which liquid and hexatic phases coexist. The interval decreases with increasing temperature and tends to vanish at . When , however, the hexatic-liquid transition becomes continuous. Therefore, in soft-core systems with reentrant crystallization, density should affect the nature of the hexatic-liquid transition.  

At much higher densities after several reentrance, we surprisingly observe the existence of two-dimensional quasicrystals. Up to now, quasicrystals have been found in multi-component systems such as alloys and in mono-component systems with multiple length scales in particle interactions or with anisotropic particles such as tetrahedral and patchy particles. In all these systems, multiple length scales are present in particle size, interaction, or anisotropy, which seem to be the consensual condition for quasicrystals to occur. The quasicrystals that we found are unexpectedly formed by monodisperse, isotropic particles interacting via the simple soft-core potential without multiple length scales. We find not only dodecagonal but also octagonal quasicrystals, which have not been found yet in soft quasicrystals. In our quasicrystals, particles tend to form pentagons. A pentagon surrounded by an n-fold polygon constructs the complex structural unit to develop the n-fold quasicrystalline order. In liquid states prior to the liquid-solid transition, we already observe some signs of the development of the quasicrystalline order, including the accumulation of pentagons and the emergence of two competing length scales. We have also verified that our quasicrystals are stable by showing that their formation is independent of history and they have the lowest inherent structure potential energy, compared with other crystalline states.

报告人简介 

徐宁，中国科学技术大学物理学院教授、副经理。2005年12月博士毕业于耶鲁大学，2006年1月至2009年7月在宾夕法尼亚大学和芝加哥大学做博士后研究，2009年7月至2010年1月在香港中文大学任研究助理教授，2010年1月起在中国科学技术大学物理学院任教。长期从事软凝聚态物理领域的基础研究，主要研究内容包括软物质非晶液-固转变、结晶熔融、非平衡态统计物理、力学超材料等基础物理问题。至今在相关研究领域共发表了50篇SCI论文，其中包括1篇Nature、1篇Nature Physics、1篇Nature Communications和18篇Physical Review Letters。先后入选中科院百人计划、国家杰青、百千万人才工程国家级人选、创新人才推进计划科技创新领军人才、万人计划领军人才。