Time-resolved collapse and revival of the Kondo state near a quantum phase transition
Ch. Wetli, S. Pal, J. Kroha, K. Kliemt, C. Krellner, O. Stockert, H. von Loehneysen, M. Fiebig
备注：
Published version, including data on CeCu6, CeCu5.9Au0.1, and CeCu5Au1 and extended Supplementary Information. 7 pages, 4 figures, Supplementary Information: 5 pages, 3 figures
多体物理学最成功的范例之一是准粒子的概念：强相互作用物质中的激发行为就像自由空间中的弱相互作用粒子。金属中的准粒子是非常坚固的物体。然而，当一个系统的基态在量子临界点（QCP）发生质变时，准粒子可能会分裂并让位于一种奇异的量子流体态。这种崩溃的性质是激烈的争论，因为涌现的量子流体在高温下控制着材料的性质，甚至可能与某些化合物中超导性的发生有关。在这里，我们跟踪CeCu $_{6-x}$ Au $_{x}$中的重费米子准粒子的动力学，并在多体计算的支持下，在时间分辨实验中监测它们向QCP的演化。太赫兹脉冲破坏了多体重费米子态。在延迟的相位相干太赫兹反射的发射下，重费米子状态恢复，相干时间比通常与相关金属相关的时间长100倍。准粒子的重量崩溃的QCP，但其形成温度保持不变-现象被认为是相互排斥的。在同一个实验中的共存要求我们对量子临界性的看法进行修正。
英文摘要：
One of the most successful paradigms of many-body physics is the concept of quasiparticles: excitations in strongly interacting matter behaving like weakly interacting particles in free space. Quasiparticles in metals are very robust objects. Yet, when a system's ground state undergoes a qualitative change at a quantum critical point (QCP), the quasiparticles may disintegrate and give way to an exotic quantum-fluid state of matter. The nature of this breakdown is intensely debated, because the emergent quantum fluid dominates the material properties up to high temperature and might even be related to the occurence of superconductivity in some compounds. Here we trace the dynamics of heavy-fermion quasiparticles in CeCu$_{6-x}$Au$_{x}$ and monitor their evolution towards the QCP in time-resolved experiments, supported by many-body calculations. A terahertz pulse disrupts the many-body heavy-fermion state. Under emission of a delayed, phase-coherent terahertz reflex the heavy-fermion state recovers, with a coherence time 100 times longer than typically associated with correlated metals. The quasiparticle weight collapses towards the QCP, yet its formation temperature remains constant -- phenomena believed to be mutually exclusive. Coexistence in the same experiment calls for revisions in our view on quantum criticality.
The thermopower as a fingerprint of the Kondo breakdown quantum critical point
我们提出，热电势区分两个竞争的情况下，量子相变在重费米子：自旋密度波（SDW）理论和击穿的近藤效应。在近藤崩溃的情况下，塞贝克系数原来从温度标度$E^{*}$，与费米表面重构的量子涨落崩溃。这一特征与SDW理论的物理性质有着根本的不同，在SDW理论中，费米面不会发生重构，这一特征可以被认为是近藤击穿理论的标志。我们测试这些想法，对YbRh $_2$ Si $_2$的实验结果。
Prethermalization and transient dynamics of the Multi-Channel Kondo systems under generic quantum quenches: Insights form Large-$N$ Schwinger-Keldysh approach
