Doubling of Landau levels in GaAs/AlGaAs heterostructures

Abstract

Usually the Landau levels are given by (n+1/2)\hbarω_c with \hbarω_c=eB/mc. We find that there are clusters of electrons with localization so that the orbital angular momentum is not zero. There are interactions which transfer the electrons from {\it l}=0 to {\it l}\ne 0 so that there is doubling in the Landau levels with \hbarω_c= (1/2)g_\pmeB/mc where (1/2)g_\pm=({\it l}+(1/2)\pm s)/(2{\it l}+1) For s=\pm 1/2 two distinct values of ω_c appear whereas only one seems to be known in the literature. This is because only one value s=+1/2 is populated. When microwaves of a suitable frequency such as 13.1 GHz at a field of about 2.5 Tesla, are turned on, s=-1/2 also gets populated. For singlets s=0, (1/2)g_\pm=1/2 so that ω_c=(1/2)(eB/mc). This will double the number of oscillations in the resistivity as a function of magnetic field. This theory of doubling of the oscillations agrees with the experimental data on GaAs/AlGaAs.