Spectroscopic evidence of quantum Hall interlayer tunneling gap collapse caused by tilted magnetic field in a GaAs/AlGaAs triple quantum well

Magnetophotoluminescence and magnetotransport were studied in a GaAs/AlGaAs triple quantum well. Oscillations of the photoluminescence intensity observed in tilted magnetic fields were found to correspond to the interlayer tunneling quantum Hall gap collapses detected in magnetoresistance measurements and predicted to occur in tilted magnetic fields. The obtained experimental data were shown to agree well with the theory developed for double quantum wells. This implies that the observed quantum Hall gap collapses are mostly caused by the tunneling between a pair of quantum wells. Our results reveal spectroscopic evidence of the quantum Hall gap collapses. Indications of interlayer correlation effects influencing a character of the inter-Landau-level gaps were found.

Figure 1

Zero-field electronic energy structure (black line) and the charge-density profiles (colored lines) self-consistently calculated for the GaAs/AlGaAs triple-quantum-well structure with the total electron sheet density $n_s=7\times {10}^{11}$ cm${}^{-2}$. The inset shows the schematic of the size-quantized states in the conduction band with interlayer tunneling gaps ${\Delta }_{12},{\Delta }_{23}$, and ${\Delta }_{13}$.

Figure 2

${\sigma }^{-}$ polarized PL intensity measured at the tilt angle $\theta ={55}^{\circ }$ in the GaAs/AlGaAs triple quantum well as a function of the perpendicular component of the magnetic field at the temperature $T=300$ mK. White dots indicate the PL peak positions. The inset shows representative PL spectra measured at a magnetic field of 0 T and $\theta =0^{\circ }$ (thin yellow line) and 10 T and $\theta ={55}^{\circ }$ (thick white line).

Figure 3

Landau-level energy structure of the GaAs/AlGaAs triple quantum well. The position of the Fermi level calculated with the total electron sheet density $n_s=7\times {10}^{11}$ cm${}^{-2}$ is shown by the black line. The numbers depict corresponding filling factors. The related cyclotron ${\Delta }_c$, Zeeman ${\Delta }_Z$, and interlayer tunneling gaps ${\Delta }_{12},{\Delta }_{23}$, and ${\Delta }_{13}$ are indicated by vertical bars.

Figure 4

(a) Plot of the magnetoresistance measured at the temperature $T=50$ mK in the GaAs/AlGaAs triple quantum well as a function of the tilting angle. The white line corresponds to the tilting angle $\theta ={55}^{\circ }$. Open gray circles indicate the collapses observed in both the magnetoresistance and photoluminescence measurements. (b) Magnetoresistance traces measured at tilt angles $\theta =0^{\circ }$ (black line) and $\theta ={55}^{\circ }$ (red line). (c) ${\sigma }^{+}$ (triangles) and ${\sigma }^{-}$ (circles) normalized photoluminescence intensities measured at $T=300$ mK in the GaAs/AlGaAs triple quantum well as a function of the perpendicular magnetic field component at $\theta =0^{\circ }$ (open symbols) and at $\theta ={55}^{\circ }$ (solid symbols). The positions of the intersubband quantum Hall gap collapses calculated according to Eq. (1) for the corresponding filling factors are shown by arrows.