Mahani M R, Pertsova A, Canali C M
Department of Physics and Electrical Engineering, Linnæus University, Norra Vägen 49, 391 82, Kalmar, Sweden.
J Phys Condens Matter. 2014 Oct 1;26(39):394006. doi: 10.1088/0953-8984/26/39/394006. Epub 2014 Sep 12.
Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1 1 0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 10(4) atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.
我们使用微观有限簇紧束缚模型，研究了位于（1 1 0）GaAs表面附近的单个Mn杂质的磁各向异性能随簇尺寸的变化趋势。我们给出了包含约10⁴个原子的大簇尺寸的计算结果，这些结果迄今尚未被研究过。我们的计算表明，在之前的紧束缚计算中发现体相GaAs中Mn掺杂剂的各向异性能非零，这纯粹是一种有限尺寸效应，会随着簇尺寸的倒数而消失。与此相反，我们发现三个带隙内Mn受主能级的分裂在无限簇尺寸的极限下收敛到一个有限值。对于体相GaAs中的Mn，这一特征与杂质与其最近邻原子之间耦合的平均场处理性质有关。我们还计算了随着Mn掺杂剂从表面移向簇中心时，子层中各向异性能的变化趋势。与之前的计算相比，这里使用大簇尺寸使我们能够将杂质置于表面下方更深的子层中。特别是，我们表明各向异性能在第五个子层之前增加，然后随着杂质进一步远离表面而减小，趋近于其体相值。本研究为通过先进的扫描隧道显微镜技术对半导体表面单个Mn掺杂剂的电子和磁性进行实验控制和操纵提供了重要的见解。
