No abstract

The spin–orbit coupling (SOC) in semiconductors is strongly influenced by structural asymmetries, as prominently observed in bulk crystal structures that lack inversion symmetry. Here we study an additional effect on the SOC: the asymmetry induced by the large interface area between a nanowire core and its surrounding shell. Our experiments on purely wurtzite GaAs/AlGaAs core/shell nanowires demonstrate optical spin injection into a single free-standing nanowire and determine the effective electron g-factor of the hexagonal GaAs wurtzite phase. The spin relaxation is highly anisotropic in time-resolved micro-photoluminescence measurements on single nanowires, showing a significant increase of spin relaxation in external magnetic fields. This behaviour is counterintuitive compared with bulk wurtzite crystals. We present a model for the observed electron spin dynamics highlighting the dominant role of the interface-induced SOC in these core/shell nanowires. This enhanced SOC may represent an interesting tuning parameter for the implementation of spin–orbitronic concepts in semiconductor-based structures.

We demonstrate the direct detection of spontaneous polarization in the wurtzite crystal phase of gallium-arsenide (GaAs) nanowires. Using differential phase contrast microscopy (DPC) in a scanning transmission electron microscope, we map the differences in charge distribution between the zinc-blende and wurtzite crystal phases and use twin defects in the zinc-blende phase to quantify the polarization strength. The value of 2.7 × 10−3 C/m2 found for the polarization strength matches well with theoretical predictions.

Nanowire geometry and crystalline structure under Mn supply Figure S1(a) and S1(b) show scanning electron microscopy (SEM) images of regular, Mn-free GaAs nanowires, grown as a control experiment, and nanowires grown under (Ga,Mn)Assupply ( rst sample series described in the article). On both samples the wires display the same length, indicating that the supply of Mn does not inhibit the VLS growth mechanism.The only di erence visible in SEM concerns the catalyst droplet: solidi ed Ga-droplets are perfectly spherical ( Figure S1(a)), while solidi ed (Ga,Mn)-alloy droplets are partially faceted ( Figure S1(b)). The results obtained in SEM for the second sample series described in the article (GaAs NWs with liquid Ga droplet exposed to Mn) are identical to Figure S1(b). The results obtained in SEM for the third sample series (GaAs NWs exposed to Mn 1