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arXiv 0902.3119cond-mat.str-el
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表面各向异性磁性杂质中近藤共振的分裂

Splitting of the Kondo resonance in anisotropic magnetic impurities on surfaces

Rok Zitko, Robert Peters, Thomas Pruschke

摘要:

利用数值重整化群方法,研究了各向异性磁性杂质Kondo模型中不同方向施加磁场时Kondo共振的分裂.考虑了几种类型的磁各向异性:XXZ交换耦合各向异性J_perp J_z、纵向磁各向异性DS_z ^[2]和横向磁各向异性E(S_x^2-S_y^2)。在自旋1/2模型与XXZ交换耦合各向异性,我们发现很小的方向依赖的分裂的大小。在自旋为3/2的易平面(D>0)各向异性模型中,我们观察到非常不相等的幅度,在存在额外的横向各向异性的情况下,x和y方向之间存在进一步的差异。一个简单而直观的解释是,分裂在软磁方向上更大。分裂的大小与自旋态之间的能量差直接相关,并且由于Kondo屏蔽,它仅被一些乘法因子微弱地修改。S=3/2模型的结果与最近对吸附在Cu(100)表面上的CuN岛上的Co杂质的扫描隧道光谱研究结果吻合得很好[A. F. Otte等人,Nature Physics 4,847(2008)]

英文摘要:

Using the numerical renormalization group method, we study the splitting of the Kondo resonance by a magnetic field applied in different directions in the Kondo model for anisotropic magnetic impurities. Several types of magnetic anisotropy are considered: the XXZ exchange coupling anisotropy J_perp J_z, the longitudinal magnetic anisotropy DS_z^2, and the transverse magnetic anisotropy E(S_x^2-S_y^2). In the spin-1/2 model with the XXZ exchange coupling anisotropy we find very small direction dependence in the magnitude of the splitting. In the spin-3/2 model with the easy-plane (D>0) anisotropy, we observe very unequal magnitudes with further differences between x and y directions in the presence of an additional transverse anisotropy. A simple and rather intuitive interpretation is that the splitting is larger in magnetically soft directions. The magnitude of the splitting is directly related to the energy differences between spin states and it is only weakly modified by some multiplicative factor due to Kondo screening. The results for the S=3/2 model are in good agreement with recent scanning tunneling spectroscopy studies of Co impurities adsorbed on CuN islands on Cu(100) surfaces [A. F. Otte et al., Nature Physics 4, 847 (2008)]

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