论文标题
量子杂质中的重新入侵近代效应与金属 - 溶性杂种触点耦合
Reentrant Kondo effect in a quantum impurity coupled to a metal-semiconductor hybrid contact
论文作者
论文摘要
使用NRG,我们表明一个包含量子杂质(QI)的系统强烈耦合到半导体(gap $2δ$),并且与金属弱耦合,在低温下显示了“重新入学”近代阶段。对相应的单个杂质Anderson模型(SIAM)的NRG分析表明,恢复阶段的特征是SIAM固定点的第二个序列:游离轨道(FO)>局部力矩(LM)>强耦合(SC)。在第一阶段,SC固定点(Kondo温度$ t_ {k1} $)是不稳定的,而第二阶段则表现出与稳定的SC固定点相关的Kondo温度$ T_ {K2} $。结果表明,重入的近托筛选与有效的暹罗相关联,有效的排斥$ u_ {eff} $。我们将这种低温有效的暹罗(我们称为“重进入”暹罗)作为高温(裸露)暹罗的“复制品”。出现的直观图片是,第一个近野国家通过半导体进行磁不筛查而发展,而第二个北极状态则涉及金属电子筛选,一旦半导体无法触及热激发($ t <δ$)($ t <δ$),并且只有金属频谱在缝隙内才能进行impurity筛选。此外,我们分析了由扶手椅石墨烯纳米甲(AGNR)和扫描隧道显微镜(STM)尖端之间形成的杂种系统,该杂交系统的各个耦合设置为重现上述通用模型。可以通过电场引起的Rashba旋转轨道相互作用来对AGNR中的能量隙进行调节。我们使用NRG分析了该系统的现实参数值,并得出结论,其及其相关的第二阶段近相传的暹罗值得进行实验研究。
Using NRG, we show that a system containing a quantum impurity (QI), strongly coupled to a semiconductor (gap $2 Δ$) and weakly coupled to a metal, displays a 'reentrant' Kondo stage at low temperatures. The NRG analysis of the corresponding Single Impurity Anderson Model (SIAM) shows that the reentrant stage is characterized by a second sequence of SIAM fixed points: free orbital (FO) > local moment (LM) > strong coupling (SC). In the first stage, the SC fixed point (Kondo temperature $T_{K1}$) is unstable, while the second stage exhibits a much lower Kondo temperature $T_{K2}$, associated to a stable SC fixed point. The results indicate that the reentrant Kondo screening is associated to an effective SIAM, with an effective repulsion $U_{eff}$. This low temperature effective SIAM, which we dub as 'reentrant' SIAM, behaves as a 'replica' of the high temperature (bare) SIAM. The intuitive picture that emerges is that the first Kondo state develops through impurity screening by semiconducting electrons, while the second Kondo state involves screening by metallic electrons, once the semiconducting electrons are out of reach to thermal excitations ($T < Δ$) and only the metallic spectral weight inside the gap is available for impurity screening. In addition, we analyze a hybrid system formed by a QI `sandwiched' between an armchair graphene nanoribbon (AGNR) and a scanning tunneling microscope (STM) tip, with respective couplings set to reproduce the generic model described above. The energy gap in the AGNR can be externally tuned by an electric-field-induced Rashba spin-orbit interaction. We analyzed this system for realistic parameter values, using NRG, and concluded that the reentrant SIAM, with its associated second stage Kondo, is worthy of experimental investigation.