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首页> 外文期刊>Physical review >Thermopower of an SU(4) Kondo resonance under an SU(2) symmetry-breaking field
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Thermopower of an SU(4) Kondo resonance under an SU(2) symmetry-breaking field

机译：SU（2）对称破坏场下SU（4）近藤共振的热功率

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摘要

We calculate the thermopower of a quantum dot described by two doublets hybridized with two degenerate bands of two conducting leads, conserving orbital (band) and spin quantum numbers, as a function of the temperature T and a splitting S of the quantum dot levels that breaks the SU(4) symmetry. The splitting can be regarded as a Zeeman (spin) or valley (orbital) splitting. We use the noncrossing approximation (NCA), the slave bosons in the mean-field approximation (SBMFA), and also the numerical renormalization group (NRG) for large δ. The model describes transport through clean C nanotubes and in Si fin-type field-effect transistors, under an applied magnetic field. The thermopower as a function of temperature S(T) displays two dips that correspond to the energy scales given by the Kondo temperature T_k and δ and one peak when k_B T reaches the charge-transfer energy. These features are much more pronounced than the corresponding ones in the conductance, indicating that the thermopower is a more sensitive probe of the electronic structure at intermediate or high energies. At low temperatures (T ? T_k), T_k S(T)/T is a constant that increases strongly near the degeneracy point δ = 0. We find that the SBMFA fails to provide an accurate description of the thermopower for large δ. Instead, a combination of Fermi liquid relations with the quantum-dot occupations calculated within the NCA gives reliable results for T ? T_k.
机译：我们计算由两个双峰与两个导电引线的两个简并带杂交得到的量子点的热功率，守恒的轨道（带）和自旋量子数与温度T和断裂的量子点能级S的函数有关SU（4）对称性。分裂可以看作是塞曼（自旋）分裂或谷（​​轨道）分裂。我们使用非交叉近似（NCA），均值近似中的从玻色子（SBMFA），以及大δ的数值重归一化组（NRG）。该模型描述了在施加磁场的情况下，通过干净的C纳米管和Si鳍型场效应晶体管的传输。作为温度S（T）的函数的热功率显示出两个骤降，分别对应于近藤温度T_k和δ给出的能级，以及一个k_B T达到电荷转移能量时的峰值。这些特征在电导率上比相应的特征要明显得多，这表明在中能或高能下，热功率是电子结构的更灵敏的探测器。在低温（T？T_k）时，T_k S（T）/ T是一个常数，在简并点δ= 0附近会大大增加。我们发现SBMFA无法提供大δ的热功率的准确描述。取而代之的是，费米液体关系与在NCA中计算出的量子点职业的结合给出了T的可靠结果。 T_k。

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