Magnetophotoluminescence of Modulation-Doped CdTe Multiple Quantum Wells.

Modulation-doped CdTe quantum wells (QWs) with Cd0.7Mg0.3Te barriers were studied by photoluminescence (PL) and far-infrared Fourier spectroscopy under a magnetic field at 4.2 K and by Raman spectroscopy at room temperature. Two samples were tested: a sample which contained ten QWs (MQW) and a sample with one QW (SQW). The width of each QW was equal to 20 nm, and each of them was modulation-doped with iodine donors introduced in a 4 nm thick layer. The concentration of donors in each doped layer was nominally identical, but the thickness of the spacer in SQW and MQW samples was 20 and 10 nm, respectively. This resulted in a two times higher electron concentration per well in the MQW sample than in the SQW sample. We observed differences in PL from the two samples: the energy range of PL was different, and one observed phonon replicas in MQW which were absent in the SQW sample. An analysis of oscillations of the PL intensity as a function of magnetic field indicated that PL resulted from the recombination of free electrons in the conduction band with free or localized holes in the case of SQW and MQW samples, respectively.

Mesoscopic Transport in Electrostatically Defined Spin-Full Channels in Quantum Hall Ferromagnets.

In this work, we use electrostatic control of quantum Hall ferromagnetic transitions in CdMnTe quantum wells to study electron transport through individual domain walls (DWs) induced at a specific location. These DWs are formed due to the hybridization of two counterpropagating edge states with opposite spin polarization. Conduction through DWs is found to be symmetric under magnetic field direction reversal, consistent with the helical nature of these DWs. We observe that long domain walls are in the insulating regime with a localization length of 4-6 µm. In shorter DWs, the resistance saturates to a nonzero value at low temperatures. Mesoscopic resistance fluctuations in a magnetic field are investigated. The theoretical model of transport through impurity states within the gap induced by spin-orbit interactions agrees well with the experimental data. Helical DWs have the required symmetry for the formation of synthetic p-wave superconductors. The achieved electrostatic control of a single helical domain wall is a milestone on the path to their reconfigurable network and ultimately to a demonstration of the braiding of non-Abelian excitations.