Probing the Fermi surfaces of coupled double quantum wells in the presence of an in-plane magnetic field

Abstract

The anticrossing of the dispersion relations of two two-dimensional electron gases (2DEGs) in an in-plane magnetic field results in distorted Fermi surfaces, leading to density of states and effective mass changes. We have used two different techniques to probe such changes with both the in-plane field and carrier density being systematically altered. The first technique uses a fixed perpendicular field to form Landau levels. By following the evolution of these Landau levels with in-plane field, carrier density and temperature, we are able to determine changes in the subband populations and effective masses. The second technique uses a third conducting layer as a detector of chemical potential changes in the coupled electron gases. This method also allows the determination of effective mass changes in an in-plane field. Calculations of the dispersion curves have been made, illustrating the effect of the parallel field upon subband occupancy and effective mass. These calculations are compared with the experimental data from both methods and are found to be in good agreement.

Anomalous integer quantum Hall states in coupled double quantum wells and the effect of Landau level broadening

“…Where independent control of both the in-plane and perpendicular field components are necessary the sample has been mounted on an in situ rotating probe. Controlled field application coupled with computational control of the sample angle to the applied field (within <0.1 • ) allows gate-sweeps at any combination of in-plane/perpendicular field (within the magnet's range) [28].…”

Tunneling spectroscopy of spin-split states in quantum wells

“…First structures of this kind have been fabricated more than a decade ago. 9,10 Since then, the interlayer tunneling in such structures has been the subject of numerous experimental [9][10][11][12][13][14][15] and theoretical 13,16 -22 studies. Measurements of the tunneling current in such structures [9][10][11][12][13] revealed peaks of the tunneling conductance in conditions in which the 2D levels in the two wells are aligned, reflecting the shape of the spectral functions within each layer, in accordance with theoretical predictions.…”

Observation of magnetic breakdown in coupled double quantum wells

“…By applying a magnetic field parallel to the 2DEG's (B ʈ ) the relative canonical momentum (បk) of the electron gases is changed by (eB ʈ d), where d is the separation of the two 2DEG's. The anticrossing of the displaced dispersion relations then results in distorted Fermi surfaces with both effective masses 4,5 and carrier densities 1 becoming strong functions of the in-plane field. Previous authors 1 have shown that the Fermi surface distortions may be accurately modeled using a semiclassical approach and that the observed changes in the effective mass are in good agreement with theory.…”