非晶态物质原子局域连接度与弛豫动力学

非晶态物质的本质及形成过程是凝聚态物理领域最困难也是最有趣的问题之一.非晶形成过程在原子结构上不会衍生出人们在传统晶体结构里所熟悉的长程有序性,因此对于此类在自然界中广泛存在的物质形态,至今还没有有效的实验表征手段和理论研究方法.非晶态物质的原子结构及其构效关系的研究是凝聚态物理和材料科学等众多研究领域所关注的热点问题之一.随着对非晶态物质物性研究的深入,人们逐渐意识到非晶态物质中原子中程序对系统性质的重要影响,建立以中程序为基础的结构-动力学关系对于理解玻璃及玻璃转变的本质起着重要的作用.本文简要综述了基于图论提出的原子局域连接度这一新的结构序参量在液体和玻璃的结构及构效关系研究中的应用.新的结构序参量从过去侧重于关注局域原子团簇的种类和分布,转移到更加关注某一类具有特殊对称性的原子的空间连接情况,即更多地尝试从原子中程序的角度来建立非晶态物质中的构效关系.新的研究结果表明,局域连接度可与非晶态物质中原子的短时或长时动力学行为、输运方式、以及振动模态等一系列物理性质建立联系.

Linking local connectivity to atomic-scale relaxation dynamics in metallic glass-forming systems

For a long time,it has been well recognized that there exists a deep link between the fast vibrational excitations and the slow diffusive dynamics in glass-forming systems.However,it remains as an open question whether and how the short-time scale dynamics associated with vibrational intrabasin excitations is related to the long-time dynamics associated with diffusive interbasin hoppings.In this paper we briefly review the research progress that addresses this challenge.By identifying a structural order parameter—local connectivity of a particle which is defined as the number of nearest neighbors having the same local spatial symmetry,it is found that the local connectivity can tune and modulate both the short-time vibrational dynamics and the longtime relaxation dynamics of the studied particles in a model of metallic supercooled liquid.Furthermore,it reveals that the local connectivity leads the long-time decay of the correlation functions to change from stretched exponentials to compressed ones,indicating a dynamic crossover from diffusive to hyperdiffusive motions.This is the first time to report that in supercooled liquids the particles with particular spatial symmetry can present a faster-than-exponential relaxation that has so far only been reported in out-ofequilibrium materials.The recent results suggest a structural bridge to link the fast vibrational dynamics to the slow structural relaxation in glass-forming systems and extends the compressed exponential relaxation phenomenon from earlier reported out-of-equilibrium materials to the metastable supercooled liquids.