Transfering spin into an extended π orbital of a large molecule
Transfering spin into an extended π orbital of a large molecule
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DOI：
10.1103/physrevb.91.144415
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发表时间：
2015-04-20
影响因子：
3.7
通讯作者：
Tautz, F. Stefan
中科院分区：
文献类型：
--
作者：
Esat, Taner;Deilmann, Thorsten;Tautz, F. Stefan
利用低温扫描隧道显微镜(STM)和能谱(STS)研究了金原子在物理吸附在Au(111)表面的PTCDA单层上的吸附。Au原子和PTCDA分子之间的化学反应导致形成一个在其最高占据轨道上有一个未配对电子的自由基。这个轨道是一个圆周率轨道，它覆盖了整个Au-PTCDA络合物。由于该轨道上有很大的库仑斥力，当分子吸附在Au(111)表面时，未成对的电子会产生局域力矩。我们通过观察源于Kondo效应的零偏微分电导峰，证明了自由基的形成和吸附后局部力矩的存在。通过零偏置微分电导随温度变化的测量，我们确定Kondo温度为T-K=(38+/-8)K。为了从理论上描述Au-PTCDA络合物的性质，我们使用了一系列方法，从包括van der Waals修正的密度泛函理论(DFT)到多体微扰理论(MBPT)和数值重整化群(NRG)方法。对于高能轨道谱，我们用自旋极化的DFT/MBPT和NRG得到了很好的一致性。此外，NRG提供了自旋自由度的低能激发谱的准确描述，预测的Kondo温度非常接近实验值。这是通过详细分析各种T-K定义的普适性，并考虑到分子-金属络合物和金属衬底之间的耦合函数的全部能量依赖性来实现的。
By means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS), we have investigated the adsorption of single Au atoms on a PTCDA monolayer physisorbed on the Au(111) surface. A chemical reaction between the Au atom and the PTCDA molecule leads to the formation of a radical that has an unpaired electron in its highest occupied orbital. This orbital is a pi orbital that extends over the whole Au-PTCDA complex. Because of the large Coulomb repulsion in this orbital, the unpaired electron generates a local moment when the molecule is adsorbed on the Au(111) surface. We demonstrate the formation of the radical and the existence of the local moment after adsorption by observing a zero-bias differential conductance peak that originates from the Kondo effect. By temperature dependent measurements of the zero-bias differential conductance, we determine the Kondo temperature to be T-K = (38 +/- 8) K. For the theoretical description of the properties of the Au-PTCDA complex we use a hierarchy of methods, ranging from density functional theory (DFT) including a van der Waals correction to many-body perturbation theory (MBPT) and the numerical renormalization group (NRG) approach. Regarding the high-energy orbital spectrum, we obtain an excellent agreement with experiments by both spin-polarized DFT/MBPT and NRG. Moreover, the NRG provides an accurate description of the low-energy excitation spectrum of the spin degree of freedom, predicting a Kondo temperature very close to the experimental value. This is achieved by a detailed analysis of the universality of various definitions of T-K and by taking into account the full energy dependence of the coupling function between the molecule-metal complex and the metallic substrate.