Article No. spmi.1998.0635 Available online at http://www.idealibrary.com on Superlattices and Microstructures, Vol. 25, No. 1/2, 1999 Effects of intersubband coupling on Friedel oscillations in quasi-two-dimensional electron systems G.-Q. HAI Instituto de F´ ısica de S ˜ ao Carlos, Universidade de S ˜ ao Paulo, 13560-970, S˜ ao Carlos, SP, Brazil F. M. P EETERS Departement Natuurkunde, Universiteit Antwerpen (UIA), B-2610 Antwerpen, Belgium N. S TUDART, G. E. MARQUES Departamento de F´ ısica, Universidade Federal de S˜ ao Carlos, 13565-905 S ˜ ao Carlos, SP, Brazil (Received 26 October 1998) We have studied the effect of screening on an ionized impurity and Freidel oscillations in a quasi-two-dimensional (Q2D) electron system in which multisubbands are occupied. The screening effects of the Q2D electron gas are investigated within the random-phase approximation. We show that in a quantum well in which two subbands are occupied, the intersubband coupling significantly deepens the first minimum in the Friedel oscillation. c  1999 Academic Press Key words: impurity, screening, quantum well, Friedel oscillation. 1. Introduction Forty years ago, Friedel showed that the screening of a charged point impurity in a simple metal results in long-range modulations in the charge density caused by the abrupt change in the density of states at the Fermi energy. Recently, the direct imaging of charged impurities in the subsurface region and the charge density oscillation around such an impurity, i.e. Friedel oscillations, were observed on the surface of GaAs in scanning tunneling microscopy (STM) [1, 2]. The electron charge density oscillations as a response to a local perturbation provides a clue to investigate the electron states and many-body properties of the system [3, 4]. Superconductivity induced by Friedel oscillations was predicted for the three-dimensional electron gas in the low-density limit. Recently, it was shown that, in a two-dimensional (2D) system, attraction occurs already at a high density. But most of the theoretical work on the Friedel oscillation was done in 3D systems or ideal 2D or 1D (one-dimensional) electron systems. In such a calculation the quasi-2D character is not included and consequently only one subband is occupied. It will be interesting to investigate the multi-subband case in which one has multiple electron gases present with corresponding different Fermi wavevectors, which will result in different Friedel oscillations in the screened potential. In this work, we study the Freidel oscillations in a Q2D system of a GaAs quantum well in which one or two subbands are occupied. The intersubband coupling effects of the Q2D electron gas are investigated within the random-phase approximation (RPA). The screened impurity potential is calculated in different planes parallel 0749–6036/99/020185 + 05 $30.00/0 c  1999 Academic Press