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arXiv 1702.07550cond-mat.mes-hallcond-mat.stat-mechcond-mat.str-el
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温度梯度下自旋\frac{1}{2}近藤效应的命运

Fate of the spin-\frac{1}{2} Kondo effect in the presence of temperature gradients

Miguel A. Sierra, David Sanchez, Rosa Lopez

摘要:

我们考虑一个强相互作用的量子点连接到两个不同温度的导线。我们的目的是研究大的热偏压下的近藤效应的行为。我们使用三种不同的方法,即,基于近藤哈密顿量的微扰形式主义,在大的充电能量和截断的运动方程的方法超越Hartree-Fock近似的安德森模型的从玻色子平均场论。前两种形式对于高于近藤温度的热梯度产生了近藤峰的抑制,尽管它们的有效性范围不同,但仍显示出非常好的一致性。第三种技术使我们能够在很宽的能量范围内分析态的全密度。此外,我们还研究了线性响应以外的量子输运性质(电流和热电流)。在电压驱动的情况下,我们重现分裂微分电导由于存在不同的电化学电位。在温度驱动的情况下,我们观察到一个强烈的非线性热电流作为所施加的热梯度的函数。根据参数的不同,我们可以找到非平凡的零,在电流的温度偏置的有限值。重要的是,这些热电流零点可以直接访问系统的特征能量尺度(近藤温度和充电能量)。

英文摘要:

We consider a strongly interacting quantum dot connected to two leads held at quite different temperatures. Our aim is to study the behavior of the Kondo effect in the presence of large thermal biases. We use three different approaches, namely, a perturbation formalism based on the Kondo Hamiltonian, a slave-boson mean-field theory for the Anderson model at large charging energies and a truncated equation-of-motion approach beyond the Hartree-Fock approximation. The two former formalisms yield a suppression of the Kondo peak for thermal gradients above the Kondo temperature, showing a remarkably good agreement despite their different ranges of validity. The third technique allows us to analyze the full density of states within a wide range of energies. Additionally, we have investigated the quantum transport properties (electric current and thermocurrent) beyond linear response. In the voltage-driven case, we reproduce the split differential conductance due to the presence of different electrochemical potentials. In the temperature-driven case, we observe a strongly nonlinear thermocurrent as a function of the applied thermal gradient. Depending on the parameters, we can find nontrivial zeros in the electric current for finite values of the temperature bias. Importantly, these thermocurrent zeros yield direct access to the system's characteristic energy scales (Kondo temperature and charging energy).

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