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Quantum criticality out of equilibrium in the pseudogap Kondo model

机译:伪能隙近藤模型中的量子临界失衡

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摘要

Quantum phase transitions out of equilibrium are outstanding emergent subjects in condensed matter physics with great fundamental importance and challenges. We theoretically investigate here the nonequilibrium quantum phase transition in a generic nano-setup: the pseudogap Kondo model where a Kondo quantum dot couples to two-left (L) and right (R)-voltage-biased fermionic leads with power-law density of states (DOS) with respect to their Fermi levels μ_(L/R), ρ_(c,L(R))(ω) ∝ |ω - μ_(L(R))|~r with 0 < r <1. In equilibrium (μ_L -μ_R =0) and for 0 < r < 1/2, with increasing Kondo correlations this model exhibits a quantum phase transition from a unscreened local moment (LM) phase to the Kondo screened phase. At finite bias voltages and near criticality, we discover new nonequilibrium universal scaling behaviors in conductance, conduction electron T matrix, and local spin susceptibility via a controlled frequency-dependent renormalization group (RG) approach. The current-induced decoherence is key to understanding these distinct universal nonequilibrium quantum critical regimes. The relevance of our results to experiment is discussed.
机译:量子相变失衡是凝聚态物理中突出的新兴课题,具有重要的基础性和挑战性。我们从理论上在这里研究通用纳米设置中的非平衡量子相变:伪间隙Kondo模型,其中Kondo量子点耦合到两个左(L)和右(R)电压偏置的铁电引线,幂律密度为。相对于费米能级μ_(L / R),ρ_(c,L(R))(ω)∝ |ω-μ_(L(R))|〜r的状态(DOS),0 <r <1。在平衡状态下(μ_L-μ_R= 0),当0 <r <1/2时,随着近藤相关性的增加,该模型显示出从非屏蔽局部矩(LM)相到近藤屏蔽相的量子相变。在有限的偏置电压和接近临界的情况下,我们通过受控的频率依赖性重归一化组(RG)方法发现了电导,电子T矩阵和局部自旋磁化率方面的新的非平衡通用缩放行为。电流引起的退相干是理解这些独特的通用非平衡量子临界体系的关键。讨论了我们的结果与实验的相关性。

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