Emerging local Kondo screening and spatial coherence in the heavy-fermion metal YbRh2Si2
Emerging local Kondo screening and spatial coherence in the heavy-fermion metal YbRh2Si2
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DOI：
10.1038/nature10148
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发表时间：
2011-06-16
期刊：
影响因子：
64.8
通讯作者：
Wirth, S.
中科院分区：
文献类型：
--
作者：
Ernst, S.;Kirchner, S.;Wirth, S.
量子态的纠缠既是基础物理学的核心概念，也是实现先进材料和应用的潜在工具。纠缠背后的量子叠加是局域自旋态和巡回电子态之间复杂相互作用的核心，这在某些稀磁合金中引起了近藤效应（1）。在局域自旋态密度足够高的系统中，它们不再被视为非相互作用;如果它们形成密集的周期阵列，则可以建立近藤晶格（1）。这样的近藤晶格导致了具有增强的有效质量的电荷载流子的出现，但是负责产生这些重费米子的相干近藤态的确切性质仍然存在很大争议（1-3）。在这里，我们使用原子分辨率的隧道光谱研究的一般近藤晶格系统，YbRh 2Si 2的低能量激发。我们发现，在费米能级处，导电电子与局域4f电子的杂化导致隧穿电导的降低。此外，我们观察明确的晶体场激发的Yb 3+离子。隧穿电导中的一个强烈的温度依赖性峰归因于Fano共振（4，5），该共振是由隧穿进入在低温下出现的相干重费米子态而产生的。总之，这些特征揭示了量子相干性如何在重4f电子近藤晶格中发展。我们的结果证明了实空间电子结构成像对于强电子相关性研究的有效性（6，7），特别是对于相干现象，相位共存和量子临界性。
The entanglement of quantum states is both a central concept in fundamental physics and a potential tool for realizing advanced materials and applications. The quantum superpositions underlying entanglement are at the heart of the intricate interplay of localized spin states and itinerant electronic states that gives rise to the Kondo effect in certain dilute magnetic alloys(1). In systems where the density of localized spin states is sufficiently high, they can no longer be treated as non-interacting; if they form a dense periodic array, a Kondo lattice may be established(1). Such a Kondo lattice gives rise to the emergence of charge carriers with enhanced effective masses, but the precise nature of the coherent Kondo state responsible for the generation of these heavy fermions remains highly debated(1-3). Here we use atomic-resolution tunnelling spectroscopy to investigate the low-energy excitations of a generic Kondo lattice system, YbRh2Si2. We find that the hybridization of the conduction electrons with the localized 4f electrons results in a decrease in the tunnelling conductance at the Fermi energy. In addition, we observe unambiguously the crystal-field excitations of the Yb3+ ions. A strongly temperature-dependent peak in the tunnelling conductance is attributed to the Fano resonance(4,5) resulting from tunnelling into the coherent heavy-fermion states that emerge at low temperature. Taken together, these features reveal how quantum coherence develops in heavy 4f-electron Kondo lattices. Our results demonstrate the efficiency of real-space electronic structure imaging for the investigation of strong electronic correlations(6,7), specifically with respect to coherence phenomena, phase coexistence and quantum criticality.