Title:

Transport of electrons in twodimensional lateral surface superlattices

Magnetoresistances were measured in a wide range of asymmetric and symmetric twodimensional lateral surface superlattices (2D LSSLs) and the detailed studies of the data using the existing models lead to the following conclusions. 1) In cases of strongly broken symmetry, different Fourier components do not independently contribute to the commensurability oscillations (COs) in striking agreement with the guiding centre drift model of D. E. Grant, A. R. Long and J. H. Davies [Physical Review B 61 (2000) 13127]. Moreover, it is found that the characteristics of the COs are defined by the asymmetry of the potential landscape as envisaged by this model. A previous semiclassical model [R. R. Gerhardts; Physical Review B 45 (1992) 3449] and a corresponding quantum mechanical calculation [F. M. Peeters and P. Vasilopoulos; Proceedings of 20th International Conference on the Physics of Semiconductors (ICPS20), 1990, p. 1589] are both found to be unable to account for the data. 2) In stressed rectangular superlattices, for transport along the cube axes, change of gate bias from large positive to less positive changed the dominant Fourier component in the 2D periodic potential from a diagonal to an axial Fourier component and accordingly the guiding centre drift direction switched from a diagonal to the appropriate axial direction manifested by the change of the period of COs from that of diagonal Fourier component to that of the dominant axial Fourier component. When the dominant diagonal and axial Fourier components were nearly equal in amplitude, the switching was observed by change of magnetic field at a constant gate bias, as change in the magnetic field changed the dominant Fourier component in the magnetic field dependent effective potential. These results are in complete accord with the guiding centre drift model of D. E. Grant, A. R. Long and J. H. Davies [Physical Review B 61 (2000) 13127]. Again, the previous semi classical model [R. R. Gerhardts; Physical Review B 45 (1992) 3449] and a corresponding quantum mechanical calculation [F. M, Peeters and P. Vasilopoulos; Proceedings of 20th International Conference on the Physics of Semiconductors (ICPS20), 1990, p. 1589] are both found to be unable to account for the data, particularly the phenomenon of switching. 3) In 2D LSSLs containing symmetric potential landscapes, different Fourier components do independently contribute to COs confirming the quantum mechanical calculation of F. M. Peeters and P. Vasilopoulos [Proceedings of 20th International Conference on the Physics of Semiconductors (ICPS20), 1990, p. 1589]. An interplay between the semiclassical model of D. E. Grant, A. R. Long and J. H. Davies [Physical Review B 61 (2000) 13127] and the said quantum mechanical model is found to be necessary to account for the suppression of the amplitude of COs. 4) Asymmetry suppresses quantum mechanical effects in asymmetric 2D LSSLs. 5) Symmetric, stressed, short period and high mobility 2D LSSLs showed a characteristic amplitude modulation of COs whenever one flux quantum hle passed through 1, 2, 3, ... unit cells of the lattice. This phenomenon is found to be related to flux quantization.
