物质超临界状态的转变：实验证据
Transition in the supercritical state of matter: experimental evidence
摘要：
在临界点之上有一个很大的、大部分未被研究过的相图。超临界物质传统上被认为是物理上均匀的，在类液体和类气体状态之间没有明显的区别。最近，一些建议已经提出了挑战这一观点，在这里，我们回顾了这一研究的历史。接近临界点时，持续的临界异常使超临界状态分离成两种不同的状态。大约十年前，有人提出Frenkel线（FL），对应于粒子运动的动力学转变以及相关的热力学和结构转变，给出了一种独特的和路径无关的方式将超临界状态分成两种性质不同的状态，并延伸到相图上的任意高压和温度。在这里，我们回顾了随后的几条调查路线。我们专注于超临界Ne，N $_2$，CH $_4$，C $_2$ H $_6$，CO $_2$和H $_2$ O在FL的跃迁的实验证据，通过一些技术，包括X射线，中子和拉曼散射实验检测。%除了H $_2$ O，这些实验由FL刺激，并遵循在前面的计算中映射的FL的状态点。随后，我们总结了该领域的其他发展，包括最近的扩展在FL，量子模拟，拓扑和几何的方法，以及在FL的属性的普遍性的动力学分析。最后，我们回顾了目前的理论理解的超临界状态，并列出在该领域的开放问题。
英文摘要：
A large and mostly unexplored part of the phase diagram lies above the critical point. The supercritical matter was traditionally believed to be physically homogeneous with no discernible differences between liquidlike and gaslike states. More recently, several proposals have been put forward challenging this view, and here we review the history of this research. Close to the critical point, persisting critical anomalies enable the separation of the supercritical state into two different states. About a decade ago, it was proposed that the Frenkel line (FL), corresponding to the dynamical transition of particle motion and related thermodynamic and structural transitions, gives a unique and path-independent way to separate the supercritical states into two qualitatively different states and extends to arbitrarily high pressure and temperature on the phase diagram. Here, we review several lines of enquiry that followed. We focus on the experimental evidence of transitions in deeply supercritical Ne, N$_2$, CH$_4$, C$_2$H$_6$, CO$_2$ and H$_2$O at the FL detected by a number of techniques including X-ray, neutron and Raman scattering experiments. %Except for H$_2$O, these experiments were stimulated by the FL and followed the state points of the FL mapped in preceding calculations. We subsequently summarise other developments in the field, including recent extensions of analysis of dynamics at the FL, quantum simulations, topological and geometrical approaches as well as universality of properties at the FL. Finally, we review current theoretical understanding of the supercritical state and list open problems in the field.
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