Coexistence of a two- and three-dimensional Landau states in a wide parabolic quantum well

Abstract

Shubnikov-de Haas oscillations are measured in wide parabolic quantum wells with five to eight subbands in a tilted magnetic field. We find two types of oscillations. The oscillations at low magnetic fields are shifted toward higher field with the tilt angle increasing and can be attributed to two-dimensional Landau states. The position of the oscillations of the second type does not change with increasing the tilt angle which points to a three-dimensional character of these Landau states. We calculate the level broadening due to the elastic scattering rate ⌫ϭប/2, where is the quantum time, and the energy separation between two-dimensional subbands, ⌬ i j ϭE j ϪE i , in a parabolic well. For all levels we obtain ⌫ j ϳ⌬ i j , which means that the levels overlap, supporting the observation of three-dimensional Landau states. Surprisingly, we find that the lowest subband, which has a smaller energy separation from the higher level, does not overlap with these subbands and forms a two-dimensional state.

Magnetoplasmon excitations and spin density instabilities in an integer quantum Hall system with a tilted magnetic field

“…For example, experimentally a WWW in a tilted field is found to display both three-dimensional ͑3D͒ and two-dimensional properties. 8 In some situations a WWW system could behave very much like a DQW system ͑albeit with strong tunneling͒. 9 More strikingly, the recent observation of anisotropic resistance at even filling factors in a WWW system with an in-plane field 7 shows a possible stripe phase formation induced by electron-electron interaction near a degeneracy or a level crossing point.…”

“…More recently, GaAs based semiconductor wide parabolic wells have been proposed as good candidates for observing such SDW instabilities since wide parabolic wells are essentially ideal 3D electron systems. 8,19,20 Brey and Halperin 20 proposed that the SDW instability and the transport anisotropy should be observed in a wide parabolic semiconductor quantum well system when an intermediate inplane magnetic field is applied. Similarly, correlation-driven intersubband SDW instability has been predicted by Das Sarma and Tamborenea in DQW systems at low carrier densities.…”

Magnetotransport in Al xGa x-1As quantum wells with different potential shapes

“…We varied the electron sheet density by illumination with a red light-emitting diode. We performed full self-consistent calculations of the total potential, envelope wave functions, the eigenvalues energies and electron density in quantum wells with different shapes following a procedure similar to those used for parabolic quantum wells [5,6]. Figs.1 and 2 show the electron density profile and total potential for triangular, parabolic and cubic quantum wells.…”

“…It included a 2000Å -wide Ga 1−c Al c As wells with Al content varying between 0 and 0.21, bounded by undoped Ga 1−c Al c As spacer layers with δ − Si doping on two sides [6]. The mobility of the electron gas in our samples was ∼ (100 − 350) × 10 3 cm 2 /V s and density -n s = (2 − 4) × 10 11 cm −2 , therefore our quantum wells were partially full with 1-4 subbands occupied.…”

Electronic Spectrum Study of Parabolic Gaas/Al_{x}ga_{1-X}as Superlattices

“…Recently, PQW's have been implemented to study non-linear optical properties [10,11], the quantum Hall effect [12,13], charge and spin oscillations in 3D gases [14,15], magnetic properties for the spin electronics [16,17], and band gap discontinuities in materials with outstanding characteristics [18,19].…”