具有弱相互作用自旋的双核金属有机配合物中的近藤效应
Kondo effect in binuclear metal-organic complexes with weakly interacting spins
摘要：
本文报道了一系列双核金属有机配合物[（Me（hfacac）_2）_2（bpym）]^0中的近藤效应的实验和理论研究，其中Me =镍（II），锰（II），锌（II）; hfacac =六氟乙酰丙酮，bpym =联嘧啶，吸附在Cu（100）表面。非磁性Zn_2的扫描隧道光谱没有出现近藤特征，而磁性Mn_2和Ni_2的扫描隧道光谱出现了零偏共振。Ni_2的情况是特别有趣的，因为实验表明两种吸附几何形状具有非常不同的性质。对于Ni_2配合物，我们用密度泛函理论进一步解释了这种情况。模拟结果表明，具有较大近藤温度T_K ~ 10 K的Ni_2配合物是通过双嘧啶单元与表面化学键合而形成的。第二种几何构型，我们分配给分子碎裂：我们认为，原来的双核分子分解成两块，包括Ni（六氟乙酰丙酮）_2，当接触到铜基板。对于这两种几何构型，我们的计算都支持了（S=1）型近藤效应的出现，这是由于单个Ni^{2+}离子的开放3d壳层。
英文摘要：
We report a combined experimental and theoretical study of the Kondo effect in a series of binuclear metal-organic complexes of the form [(Me(hfacac)_2)_2(bpym)]^0, with Me = Nickel (II), Manganese(II), Zinc (II); hfacac = hexafluoroacetylacetonate, and bpym = bipyrimidine, adsorbed on Cu(100) surface. While Kondo-features did not appear in the scanning tunneling spectroscopy spectra of non-magnetic Zn_2, a zero bias resonance was resolved in magnetic Mn_2 and Ni_2 complexes. The case of Ni_2 is particularly interesting as the experiments indicate two adsorption geometries with very different properties. For Ni_2-complexes we have employed density functional theory to further elucidate the situation. Our simulations show that one geometry with relatively large Kondo temperatures T_K ~ 10K can be attributed to distorted Ni_2 complexes, which are chemically bound to the surface via the bipyrimidine unit. The second geometry, we assign to molecular fragmentation: we suggest that the original binuclear molecule decomposes into two pieces, including Ni(hexafluoroacetylacetonate)_2, when brought into contact with the Cu-substrate. For both geometries our calculations support a picture of the (S=1)-type Kondo effect emerging due to open 3d shells of the individual Ni^{2+} ions.
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