高压下富氢高温超导体的新探索

Hydrogen-rich materials which are potential high-temperature superconductors, and also believed to be an effective way to the metallization of hydrogen, have attracted significant interest in lots of fields, such as physics, material science and so on. Therefore, hydrogen-rich materials are expected to become a new member of superconductor family: hydrogen-based superconductor. Very recently, the discovery of high-pressure superconductivity at 203 K (-70º) in a sulfur hydride compound has broken the previous record in copper-based superconductor of 164 K, and inspired further efforts to research the superconductivity of hydrogen-rich materials. But there are still two key scientific problems to be solved: (1) Some hydrides present very high superconducting transition temperatures (Tc), but some of them have low Tc, and the substantial physical reason is not clear. (2) Try to find one or two hydrogen-rich materials with higher Tc. So, some representative hydrogen-rich materials will be studied in this project by means of the high pressure experimental measurements combined with first-principles calculations. This project aims to explore the inner relationship between crystal structure, electronic structure, hydrogen bonding, hydrogen content and superconductivity, get a general law for hydrogen-rich materials with high Tc, based on our high pressure research for many years. Furthermore, we try to find one or two kinds of superconductors with higher Tc in hydrogen-rich materials. Through the implementation of the project, it can also provide new approach and important data for metallic hydrogen and room-temperature superconductors.

富氢材料作为潜在的高温超导体，同时也是实现金属氢的有效途径，已成为物理、材料等多学科的研究热点，有望成为超导家族的新成员-氢基超导体。最近发现了硫氢化合物在高压下的超导转变温度达到203 K（-70º），创造了高温超导新纪录，进一步推动了人们对富氢超导电性的研究。但是，仍存在两个关键科学问题亟待解决：（1）有些氢化物呈现出奇异的高温超导特性，然而某些氢化物的超导转变温度却很低，内在物理原因不清楚。（2）寻找到具有更高超导转变温度的富氢材料。本项目拟在多年高压研究基础上，选取典型的富氢材料为研究对象，采用原位高压实验测量结合第一性原理计算，揭示晶体结构特征、电子结构特性、氢的成键方式、氢含量等因素与超导电性之间的内在联系，获得影响富氢材料高温超导电性的一般规律，力争找到一、二种具有更高超导转变温度的富氢新材料。本项目的实施，还将为金属氢和室温超导材料等方面的研究提供新的途径和重要的数据。

富氢材料可以在实验室压力下实现金属化，是潜在的高温超导体，已经成为物理学、材料科学等多学科的热点领域之一。本项目利用自主搭建的金刚石对顶砧原位高压激光加热、磁化率测量等实验测量系统，结合第一性原理计算，在高压下成功制备了一系列新型富氢材料：超导温度Tc高达212K和242K的高温超导体YH6和三元La-Al-H体系，笼状结构的超氢化物PrH9和NdH9，以及新型钡超氢化物BaH12；通过横向对比分析发现，随着La-Ce-Pr-Nd核外f电子的增多，磁性增强导致超导电性减弱，其中NdH9是首次发现的具有强磁性的氢化物。理论上，设计了系列超导温度超过200K的新型富氢材料，如层状的“类五角石墨烯状”的超氢化物HfH10，其Tc高达234K，是继共价金属性H3S和笼状氢化物LaH10之后，新的高Tc氢化物材料；笼状超氢化物LuH6，其理论Tc在高压下达到了273K，已达冰点温度；新型笼状超氢化物CaH9，其理论超导温度为266K。揭示了新型富氢材料的晶体结构特征、电子结构特征、氢的成键方式、磁性等因素与超导电性之间的内在联系，获得了具有高温超导电性的一般规律，弄清了为什么有些氢化物呈现出奇异的高温超导特性而某些氢化物的超导转变温度却很低，为进一步寻找高温富氢超导体提供了理论指导，推动了新型富氢材料的研究，也为金属氢和氢基高温超导体的研究提供了新的途径和重要的实验数据。本项目在Phys Rev Lett, Nature Commun, Sci Adv, J Am Chem Soc, Phys Rev B等国际高影响力杂志发表38篇SCI论文，获得2项国家知识产权局授权实用新型专利。项目组成员在国际学术会议做邀请报告15人次；项目组成员段德芳获得国家自然科学基金委员会优秀青年科学基金的资助。