Visualizing heavy fermions emerging in a quantum critical Kondo lattice

摘要

“重费密子”材料是含有电子处在f-轨道上的元rn素的固体材料。处在f-轨道上的电子可以跟其rn他电子发生相互作用，形成具有重“有效质rn量”的低能激发。“重费密子”激发可能含有打rn开非传统超导体和其他奇异物质状态的外观之rn谜的钥匙。它们具体是怎样获得其“物质增强”rn(mass enhancement)的以前并不知道。在这rn项研究中，Ali Yazdani吸其同事通过使用扫描rn隧道显微镜来对一个Kondo晶格中的“重费密rn子”进行仔细观察，构建了关于这一过程的一rn个画面。对这些激发的寿命进行研究，还显示rn了量子临界行为的有趣特征。%In solids containing elements withforbitals, the interaction betweenf-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behaviour observed in actinide- and lanthanide-based compounds. Here we use spectroscopic mapping with the scanning tunnelling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunnelling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system.