Magnetoabsorption in InSb quantum-well heterostructures

Spin-resolved cyclotron resonance is observed in InSb/AlInSb quantum-well heterostructures. Spin-resolved transitions are identified for fields greater than 2.2 T and confirmed by $\mathbf{k}\cdot \mathbf{p}$ modeling. The cyclotron effective mass is calculated for a range of fields up to 11.5 T and is indicative of the strong nonparabolicity in this material. Resonant coupling is observed between the ground and first occupied subbands for normal-incidence excitation. This is explained in the context of conduction band-valance band mixing due to the narrow bandgap. Further resonant coupling is observed via interaction with a hybrid intersubband plasmon-LO phonon mode. This allows a quantitative estimation of the subband spacing and of the electron-phonon interactions in the quantum well.

Figure 1

Schematic of energy-level quantization in a two-subband system $\left(i=1,2\right)$ as a function of magnetic field, showing the first three Landau levels, $n=0–2$. Each Landau level is split into spin-up (down) states, dashed (solid) lines. Where Landau levels of the same spin intersect an anticrossing takes place. Inset: cyclotron resonance energy as it passes through the RSLC, noting that the resonance splits into two branches.

Figure 2

Cyclotron resonance energy positions as a function of magnetic field in the PF configuration. Hatched areas cover regions of the spectra where data are unreliable due to coincidence with the substrate restrahlen band and the quantum-well TO phonon absorption. Transitions are labeled according to Fig. 1, and resonant coupling behavior is clearly observed between 3.5 and 5.5 T and between 8.5 and 9.5 T. The calculated filling factors $\nu$ are given along the top axis. Transition energies calculated from $\mathbf{k}\cdot \mathbf{p}$ modeling are shown as solid lines.

Figure 3

Cyclotron mass deduced from spin-resolved cyclotron resonance energies as a function of magnetic field. The data points in the RMPC region have been removed for clarity. The calculated field-dependent cyclotron masses for each transition are shown as continuous lines and the linear cyclotron mass approximations are shown as dotted lines.

Figure 4

Clyclotron resonance absorption spectra for the sample mounted in the (a) PF and (b) TF $6°$ configurations for fields between 7.5 and 11.5 T. Anticrossing is clearly visible in the $0^{+}\to 1^{+}$ resonance in the PF configuration, but much less so in the $0^{-}\to 1^{-}$ resonance. In the TF configuration RSLC anticrossing is greatly enhanced in both transitions.

Figure 5

Cyclotron resonance peak position as a function of magnetic field $B$. The presence of notable anticrossing in the $0^{+}\to 1^{+}$ transition while perpendicular to the field implies coupling of the $z$ and $\left(x,y\right)$ components of the electron wave function even for perpendicular field.

Figure 6

Cyclotron resonance absorption spectra between 3.9 and 5.2 T in the region of the InSb TO and LO phonons. A significant range of energies are obscured by the TO phonon interaction. Absorption features A–F are identified.

Figure 7

Cyclotron resonance energy positions for transitions around the InSb phonon region for measurements taken in the PF configuration. Data are partly obscured around the InSb TO phonon energy. Strong anticrossing is seen in the $1^{+}\to 2^{+}$ and $0^{-}\to 1^{-}$ transitions. The InSb-LO phonon is shown as a dashed line. The calculated hybrid intersubband plasmon-LO phonon level is indicated by a dotted line at 24.15 meV.