Cyclotron-resonance oscillations in InAs quantum wells

Abstract

The cyclotron resonance of a two-dimensional electron gas in an InAs quantum well sandwiched between two GaSb layers has been investigated experimentally for its dependence on the magnetic field. Bath the amplitude and the half-width of the resonance show a strong oscillatory behavior, exhibiting a maximum amplitude and correspondingly a minimum half-width when the highest occupied Landau level is half filled. Oscillations for more than ten periods have been observed.From our experiments we can deduce that there is a considerable overlap of the Landau levels, which strongly increases with decreasing magnetic field.The cyclotron resonance (CR) in a two-dimensional electron gas (2DEG) has been investigated extensively for different systems, e.g. , Si metal-oxide-semiconductor structures, ' InSb metal-insulator-semiconductor structures, 2 GaAs heterostructures, 3 and InAs quantum wells.The dependence of the mass, amplitude, and linewidth of the CR on the magnetic field 8 shows a complex behavior. It differs for different systems and sample configurations due to different scattering and interaction mechanisms that are important for the particular situation (e.g. , Refs. 6-9). For some Al"Ga~"As-GaAs heterostructure samples, in particular of not too high electron density Nq, an oscillation of the half-width related to an odd and an even filling factor v Ngh/e8 has been ob-served3' which has been explained by an oscillatory behavior of the screening properties for a 2DEG in a strong magnetic field 8. 3"'2We have investigated CR in a 2DEG of an InAs quantum well'3 sandwiched between two GaSb layers. This system has the advantage of a relatively low effective CR mass m, with corresponding high cyclotron frequencies to, e8/m, . This allows us to study CR down to low magnetic fields and high filling factors. Also of importance is that the charge density Ns and mobility are such that the effect of the optical signal saturation (see below) does not smear out oscillations and the internal CR scattering r, can be determined.Since we can observe a large number of oscillation periods we are able to make detailed statements about the 8 dependence for the situations of both fully filled and half-filled highest Landau levels. In particular,~e can conclude from our measurements that there is a significant overlap of the density of states between the different Landau levels, as has been discussed from magnetic susceptibility, specific™heat, and magnetocapacitance measurements.The experiments~ere performed on molecular-beam-epitaxially grown samples, similar to those described in Refs. 4 and 13. On a GaAs substrate, a buffer layer of GaAs and then a thick layer of GaSb were first grown. This was followed by the InAs well of 20 nm and completed with a GaSb cap of 20 nm. All layers are nominally undoped. This system represents a type-II heterostructure with the GaSb valence band about 150 meV above the InAs conduction band. In this system electrons are transferred from the GaSb into the InAs quantum well, creating, in an ideal case, an ...

Magnetometry of low-dimensional electron and hole systems

“…They concluded that the broadening is a strongly oscillating function of the position of the chemical potential, becoming largest when the µ lies between LLs and hence screening is minimised. Similar conclusions were reached on the basis of a number of calculations [43,44] and experiments on heat capacity [45] and cyclotron resonance [46]. Smith et al [47,48] modelled magnetocapacitance data using a field-independent Gaussian DOS, but a field-dependent width (Γ ∼ √ B) has also been reported experimentally from dHvA [9] and magnetocapacitance [49] measurements, the latter requiring in addition a constant background DOS.…”

Random network models and quantum phase transitions in two dimensions

“…Despite there exist several experimental features apparently related to electron interaction [51,52,53,54,55,56,57,58,59], it seems that the integer quantization of the Hall conductance can be understood within the localization model without taking into account the correlations between the electrons [5]. On the other hand, for explaining the fractionally quantized Hall effect, interaction and correlation effects are generally accepted to constitute the necessary ingredients for generating the excitation gaps between the many-electron ground states associated with rational filling factors.…”

Dicke superradiance in solids [Invited]

“…Theoretical studies predicted that the linewidth of CR should oscillate with the LL filling factor since the screening capability (i.e., the density of states at the Fermi energy) of a 2DEG oscillates with the filling factor [153][154][155][156][157]. However, despite several decades of experimental studies of CR in 2DEGs using continuous-wave spectrometers [158][159][160][161][162][163][164], no clear evidence for the predicted CR linewidth oscillations has been obtained for high-mobility, high-density samples.…”