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Two-channel Kondo physics in odd impurity chains

机译：奇数杂质链中的两通道近藤物理学

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We study odd-membered chains of spin-j impurities, with each end connected to its own metallic lead. For antiferromagnetic exchange coupling, universal two-channel Kondo (2CK) physics is shown to arise at low energies. Two overscreening mechanisms are found to occur depending on coupling strength, with distinct signatures in physical properties. For strong interimpurity coupling, a residual chain spin- A moment experiences a renormalized effective coupling to the leads, while in the weak-coupling regime, Kondo coupling is mediated via incipient single-channel Kondo singlet formation. We also investigate models in which the leads are tunnel-coupled to the impurity chain, permitting variable dot filling under applied gate voltages. Effective low-energy models for each regime of filling are derived, and for even fillings where the chain ground state is a spin singlet, an orbital 2CK effect is found to be operative. Provided mirror symmetry is preserved, 2CK physics is shown to be wholly robust to variable dot filling; in particular, the single-particle spectrum at the Fermi level, and hence the low-temperature zero-bias conductance, is always pinned to half-unitarity. We derive a Friedel-Luttinger sum rule and from it show that, in contrast to a Fermi liquid, the Luttinger integral is nonzero and determined solely by the "excess" dot charge as controlled by gate voltage. The relevance of the work to real quantum dot devices, where interlead charge-transfer processes fatal to 2CK physics are present, is also discussed. Physical arguments and numerical renormalization-group techniques are used to obtain a detailed understanding of these problems.
机译：我们研究了自旋j杂质的奇数链，其每一端均连接至其自身的金属铅。对于反铁磁交换耦合，通用的两通道近藤（2CK）物理场在低能量下会出现。发现了两种过筛机制，这取决于偶联强度，在物理性质上具有不同的特征。对于强杂质间偶联，残余链自旋-矩经历了与导线的重新规范化的有效偶联，而在弱偶联体系中，近藤偶联是通过初期单通道近藤单线态形成来介导的。我们还研究了其中引线通过隧道耦合到杂质链的模型，允许在施加的栅极电压下可变点填充。推导了每种填充方式的有效低能模型，甚至对于链基态为自旋单线态的填充物，也发现轨道2CK效应是有效的。如果保持镜面对称性，则2CK物理表现出对可变点填充的完全鲁棒性；特别是，费米能级的单粒子光谱以及因此低温零偏压电导始终固定为半单位。我们推导了Friedel-Luttinger和规则，并据此表明，与费米液体相反，Luttinger积分为非零值，并且仅由栅极电压控制的“过量”点电荷确定。还讨论了该工作与实际量子点设备的相关性，其中存在对2CK物理致命的引线间电荷转移过程。使用物理参数和数值归一化组技术来获得对这些问题的详细理解。

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