I. INTRODUCTION There continues to be a great deal of interest in the investigation and manipulation of the spin degree of freedom of the charge carriers in semiconductor heterostructures with possible applications in the emerging field of spintronics[1]. Spintronics is based on manipulation of the spin degree of freedom of the carriers in order to develop functional mesoscopic devices with wide ranging applications, such as spin filters[2], spin field effect transistors[3], field effect switches[4], data storage[5], quantum computing[6] and even biological sensors[7]. The manipulation of the spin degree of freedom requires that we have control over the strength of spin-orbit interaction that couples the orbital motion of the electrons with the orientation of electron spins. It was first proposed by Bychkov and Rashba[8] that in the presence of Rashba spin-orbit interaction (RSOI), that arises as a result of structural inversion asymmetry, the spin of finite momentum electrons feels a magnetic field perpendicular to the electron momentum in the inversion plane. Both experimental as well as theoretical studies have shown that RSOI has an important role in semiconductor spintronic systems[1], since the strength of RSOI can be controlled by applying a gate voltage on top of the two-dimensional electron gas (2DEG)[9]. In addition to the investigation of single particle properties in the presence of RSOI, there is also serious effort to examine the effects of RSOI on the collective properties of semiconductor heterostructures. Single particle magneto-oscillatory phenomena such as the Shubnikov-de Haas and de Haas-van Alphen effects have been important in probing the elec- tronic structure of solids. Their collective analog yields important insights into collective phenomena. In a 2DEG, collective excitations are induced by electron-electron interactions. These collective excitations (plasmons) are among the most important electronic properties of a system. In the presence of an external magnetic field, these collective excitations are known as magnetoplasmons. Magnetic oscillations of the plasmon frequency occur in a mag- netic field. In this regard, there have been recent studies of collective excitations (plasmons) of two-dimensional electron gas (2DEG) systems realized in semiconductor heterostructures in the presence of RSOI with and without an external magnetic field [10–13]. These studies show that the presence of RSOI mixes the spin up and spin down states of neighboring Landau levels with the result that two new, unequally spaced branches arise. Given the importance RSOI has acquired, it is important to investigate the effects of 2