Bruce D. McCombe

University at Buffalo - SUNY

"Spin Injection and Manipulation in InAs-based Heterostructures"

Indium arsenide is an interesting material for spintronic applications because of its large spin-orbit interaction, which permits spin manipulation via electric fields High frequency spin manipulation is of particular interest because of the relatively short spin lifetimes in InAs, a negative aspect of the large spin-orbit interaction. We have investigated spin injection in InAs-based heterostructures via circularly polarized electroluminescence (EL) in the vicinity of three microns wavelength from InAs/II-Mn-VI spin-LEDs at low temperatures utilizing the giant g-factor of n-(CdMn)Se to spin-polarize electrons, which are injected into an InAs quantum well. Early samples showed qualitative similarities in the magnetic field dependence of the circular polarization degree to structures employing non-magnetic (CdSe) injectors (negative polarization degree over a large range of fields). Recent samples with larger Mn concentrations exhibit a qualitative difference, with positive polarization degree observed at fields above 1 T. A detailed rate equation model shows that the similarity of the magnetic and non-magnetic aligner results is due to low spin polarization in the CdMnSe, which results from low effective Mn concentration, and comparable spin-flip and recombination times in InAs. This model also shows that the positive polarization degree observed at low fields is evidence of spin injection.

Recent theoretical work has indicated that strong electric-dipole spin resonance (EDSR) in InAs can be used to manipulate spins via high frequency electric fields. We are studying photoresponse and transmission at THz frequencies at dc magnetic fields corresponding to electron spin resonance in high quality InAs quantum wells with carrier concentrations in the range of 10¹² cm^-2. The goal is to detect EDSR, and measure its absorption strength as a function of various parameters. Initial results show interesting and unexpected behavior of the photoresponse vs the angle between the normal to the sample surface and the applied magnetic field. A single sharp resonance is observed at a particular angle as a change in the diagonal magnetoresistance at the center of the = 7 quantum Hall resistance minimum at a magnetic field corresponding to that predicted for electron spin resonance. For smaller angles no resonance is observed, while for larger angles the single resonance splits into two very sharp lines. We believe this behavior is related to photoinduced changes in the quantum Hall edge currents associated with the EDSR absorption. These results and transmission experiments will be discussed.

Work supported by DARPA ONR# N00014-00-1-0951, NSF-DMR 0203560 and NSF-ECS 0224225