类重费米子材料的强磁场/高压物性研究

Heavy fermion compounds demonstrate rich physical properties under the extreme conditions of strong magnetic field and high pressure, being the prototype examples for studying the competing phases and their manipulation, and for revealing the emergent quantum states and critical phenomena in correlated electron systems. Recently we observed a field-induced Fermi surface reconstruction in the antiferromagnetic state of the heavy fermion metal CeRhIn5 at B*=30T. Our results provide the first evidence for the existence of multiple quantum critical points in the same material while being tuned by different parameters like pressure and magnetic field. In order to understand these findings and generalize it to other systems, in this project we will look into the origin of the field-induced Fermi surface reconstruction at B*=30T in CeRhIn5, the change of electronic states and the associated quantum critical phenomena near the antiferromagnetic quantum critical points, and the critical end points of metamagnetic instabilities or metal-insulator transition in several heavy fermions compounds (mainly Ce-115 family) as well as some d-electron materials (e.g.,CrAs). Here we tune the electron correlations by applying both magnetic field and pressure. Using the high field facilities in the High Field Laboratory of CAS (Hefei) and also other places in the world, we will study these problems by performing measurements of the low-temperature electrical resistivity, specific heat, magnetic susceptibility and thermal expansion. These experiments will allow us to map out the field-pressure-temperature phase diagram for these materials. We aim at revealing the universal classification of various type of quantum critical points and the formation of emergent quantum phases, e.g., unconventional superconductivity, in strongly correlated electron systems.

重费米子等强关联电子体系在强磁场和高压等极端条件下常表现出丰富的物理相图，是研究多量子序竞争与调控，发现新奇量子态和量子效应的理想体系。最近我们发现重费米子金属CeRhIn5在反铁磁态内出现磁致费米面重构（B*=30T)，并且在磁场和压力调控下可能呈现出不同类型的量子临界点。为了进一步认识并推广这一实验发现，本项目将利用合肥强磁场科学中心的水冷磁体等设备，以磁场和压力作为调控电子相互作用的重要参量，通过低温电阻、比热、磁化率、热膨胀系数等多种物理量的测量，研究CeRhIn5中磁致费米面重构的物理起源，揭示CeRhIn5及CrAs等类重费米子材料在反铁磁量子临界、变磁量子相变或者金属-绝缘体转变等失稳边界的量子临界效应和电子态变化，构筑这类体系的磁场-压力-温度等多参量物理相图，探索量子相变的普适物理规律。

关联电子体系在强磁场和高压等极端条件下常表现出丰富的物理相图，是研究量子序的竞争与调控，发现新奇量子态和量子效应的理想体系。本项目以磁场、压力等作为调控参量，系统研究了CeRhIn5和CeRh6Ge4等强关联电子材料的物理性质，建立了多个化合物的电子态相图，揭示了磁性量子相变的一些普适物理规律；研究了一系列潜在拓扑材料中的新颖物性，包括近藤拓扑半金属、超导电性等；研究了多种非常规超导材料的超导序参量对称性，提出了一些新的超导配对态。本项目取得了多项创新性研究成果，在Nature、Nature Communications、PNAS、PRL等期刊上发表SCI论文68篇，在重要国际会议上作邀请报告20余次。.代表性成果包括：（1）首次在纯净的重费米子化合物CeRh6Ge4中发现铁磁量子相变存在的确凿证据，并观察到奇异金属行为，打破了先前铁磁量子临界点不存在的普遍共识；（2）发现CeRhIn5表现出丰富的压力-磁场相图，其电子态的演化强烈依赖于磁场取向，电子有效质量随磁场增加而增加，表明电子在强磁场条件下呈现出退局域化；（3）完善了ZnCr2Se4的磁场-温度相图，发现了磁场驱动的量子临界区，为探索三维大自旋磁性材料的新奇量子现象提供了新思路；（4）在重费米子半金属YbPtBi中发现外尔费米子的实验证据；（5）在PbTe薄膜中发现一种实现拓扑晶体绝缘体的新途径，在ZrTe5中发现压力可以破坏狄拉克半金属态；（6）在TaTe4和(TaSe4)2I等材料体系中发现压力诱导的超导电性；（7）发现重费米子超导体CeCu2Si2不存在超导能隙节点，提出了一种新的两能带d-波超导态，合理解释了先前矛盾的实验结果；（8）通过压力下的转角电阻测量，发现CrAs的压致超导相呈现出自旋三重态超导配对。