Anomalous spatial shifts in interface electronic reflection beyond the linear approximation

Recently, the electronic analogy of the anomalous spatial shift, including Goos-Hanchen and Imbert-Fedorov effects, has been attracting widespread interest. Current research on the anomalous spatial shift in interface electronic reflection is based on the paradigm of linear approximation, under which the center position of the incident and reflected beams are obtained by expanding the phases of relevant basis states and scattering amplitudes to the first order of incident momentum. However, in a class of normal cases, the linear approximation leads to divergent spatial shifts in reflection for certain incident angles, even though the corresponding reflection possibility is finite. In this paper, we show that these nonphysical results are caused by an abrupt change in the number of the propagating states at critical parameters, and can be resolved by calculating the center positions of the scattering beams beyond the linear approximation. Moreover, we find that the beam width has an important influence on the spatial shift near the critical angles. We demonstrate our idea via concrete calculations of Goos-Hanchen and Imbert-Fedorov shift on two representative models. These results provide a deeper understanding of the anomalous spatial shift in calculations.