A25

326 Surface Science 113 (1982) 326-332 North-Holland Publishing Company

CYCLOTRON RESONANCE LINEWIDTH IN A TWO-DIMENSIONAL ELECTRON GAS C.K. SARKAR and R.J. NICHOLAS Clarendon Laboratory, Parks Road, Oxford OXI 3PU, UK

Received 15 July 1981 ; accepted for publication 25 August 1981

A density matrix formulation has been developed to study cyclotron resonance lineshape for two-dimensional electron-impurity and electron-phonon systems. Cyclotron resonance lineshape has been calculated for several different impurity and phonon scattering mechanisms including short range, Gaussian and ionised impurities, and acoustic phonons.

Surface Science 113 (1982) 333-338 333 North-Holland Publishing Company

QUANTUM TRANSPORT TECHNIQUE IN TWO-DIMENSIONAL SYSTEMS: APPLICATIONS TO CYCLOTRON RESONANCE Mahendra PRASAD Physics Department, University of New Brunswick, p.o. Box 4400, Fredericton, NB, EJB 5A3 Canada

and

Vijay K. ARORA * Physics Department, University of Riyadh, P.O. Box 2455, Riyadh, Saudi Arabia

Received l July 1981 ; accepted for publication 10 August 1981

In recent years there has been a growing interest in generalizing the quantum transport techniques in a magnetic field already available for three-dimensional systems to yield a theory of two-dimensional systems. However, a direct generalization is not.possible because the density of states and electrical conductivity of a two-dimensional electron gas possess strong delta function singularities near the cyclotron resonance frequency oJ c. In order to overcome this difficulty, proper connected diagram approximation and renormalized Born approximation have been developed which include multiple scattering of an electron with a single impurity in all orders of the perturbation. In the present paper, another method based on the memory function formalism of Mori is employed to develop quantum transport technique in two dimensions. The results obtained are comparable to those yielded by the methods used earlier. Applications to the cyclotron resonance linewidth function, which is simply the real part of the memory function, is made explicity, A minimum in the linewidth function with respect to the quantizing magnetic field is predicted. The cause of the minimum is essentially due to the :competition between the short range and long range scattering forces. Therefore the phase transition observed recently is attributed as due to a sudden transition in the relaxation mechanism of the electron gas as its number density is varied from a higher density regime towards the lower density regime. This mechanism is compared with other explanations.