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Thermoelectric transport through strongly correlated quantum dots

机译：通过强相关量子点的热电传输

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The thermoelectric properties of strongly correlated quantum dots, described by a single-level Anderson model coupled to conduction-electron leads, is investigated using Wilson's numerical renormalization-group method. We calculate the electronic contribution, K_e, to the thermal conductance, the thermopower, 5, and the electrical conductance, G, of a quantum dot as a function of both temperature, T, and gate voltage, v_g, for strong, intermediate, and weak Coulomb correlations, U, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures T_1(vg) and T_2(vg) with T_1 < T_2. We find that T_1>T_p(v_g)≈T_K(v_g), where T_p(v_g) is the position of the Kondo-induced peak in the thermopower, T_K(v_g) is the Kondo scale, and T_2=O(Γ), where Γ is the level width. The loci of T_1(v_g) and T_2(v_g) merge at a critical gate voltage, v_g=v_g~c(U/Γ) beyond which no sign change occurs at finite gate voltage (measured relative to midvalley). We determine v_g~c for different U/Γ finding that v_g~c coincides, in each case, with entry into the mixed-valence regime. No sign change is found outside the Kondo regime, or, for weak correlations U/Γ approx< 1, making such a sign change in S(T) a particularly sensitive signature of strong correlations and Kondo physics. The relevance of this to recent thermopower measurements of Kondo correlated quantum dots is discussed. The results for quantum dots are compared also to the relevant transport coefficients of dilute magnetic impurities in nonmagnetic metals: the electronic contribution, k_e, to the thermal conductivity, the thermopower, S, and the impurity contribution to the electrical resistivity, p. In the mixed-valence and empty-orbital regimes, we find, as a function of temperature, two peaks in K_e as compared to a single peak in k_e, and similarly, G(T) exhibits a finite-temperature peak on entering the mixed-valence regime whereas such a pronounced peak is absent in ρ(T) even far into the empty-orbital regime. We compare and contrast the figure of merit, power factor, and the extent of violation of the Wiedemann-Franz law in quantum dots and dilute magnetic impurities. The extent of temperature scaling in the thermopower and thermal conductance of quantum dots in the Kondo regime is discussed.
机译：使用威尔逊数值重归一化组方法研究了由单级安德森模型耦合到导电电子引线所描述的强相关量子点的热电特性。我们计算出量子点的热导率，热功率5和电导率G的电子贡献K_e与温度T和栅极电压v_g的函数关系，其中强，中和点上的弱库仑相关系数U。对于强相关性和近藤状态，我们发现热电在温度T_1（vg）和T_2（vg）且T_1 T_p（v_g）≈T_K（v_g），其中T_p（v_g）是近藤感应峰在热电势中的位置，T_K（v_g）是近藤尺度，T_2 = O（Γ），其中Γ是水平宽度。 T_1（v_g）和T_2（v_g）的轨迹在临界栅极电压v_g = v_g〜c（U /Γ）处合并，超过该极限时，在有限的栅极电压下（相对于中谷测量）没有符号变化。我们确定不同的U /Γ的v_g〜c，发现v_g〜c在每种情况下都与进入混合价态一致。在Kondo体制之外没有发现任何符号变化，或者对于弱相关U /Γ大约<1，使得S（T）中的这种符号变化成为强相关性和Kondo物理学的特别敏感的签名。讨论了其与近藤相关量子点的最新热功率测量的相关性。还将量子点的结果与非磁性金属中稀磁性杂质的相关传输系数进行了比较：电子对导热系数k_e的贡献，热功率S和对电阻率p的杂质贡献。在混合价态和空轨道状态下，我们发现，作为温度的函数，K_e中有两个峰，而k_e中只有一个峰，并且类似地，G（T）在进入混合态时表现出有限温度峰价态，而ρ（T）甚至在空轨道态中都没有这样明显的峰值。我们比较并对比了量子点和稀磁性杂质中的品质因数，功率因数以及违反Wiedemann-Franz定律的程度。讨论了近藤状态下量子点的热功率和热导率中的温度定标程度。

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