Many spintronic devices rely on the presence of spin-polarized currents at zero magnetic field. This is often obtained by spin exchange-bias, where an element with long-range magnetic order creates magnetized states and displaces the hysteresis loop. Here we demonstrate that exchange-split spin states are observable and usable in the smallest conceivable unit: a single magnetic molecule. We use a redox-active porphyrin as a transport channel, coordinating a dysprosium-based single-molecule-magnet inside a graphene nano-gap. Single-molecule transport in magnetic field reveals the existence of exchange-split channels with different spin-polarizations that depend strongly on the field orientation, and comparison with the diamagnetic isostructural compound and milikelvin torque magnetometry unravels the role of the single-molecule anisotropy and the molecular orientation. These results open a path to using spin-exchange in molecular electronics, and offer a method to quantify the internal spin structure of single molecules in multiple oxidation states.

We address the radiative emission of individual germanium extrinsic centers in Al0.3Ga0.7As epilayers grown on germanium substrates. Micro-photoluminescence experiments demonstrate the capability of high temperature emission (70 K) and complex exciton configurations (neutral exciton X and biexciton XX, positive X + and negative X − charged exciton) of these quantum emitters. Finally, we investigate the renormalization of each energy level showing a large and systematic change of the binding energy of XX and X + from positive to negative values (from ∼+5 meV up to ∼-7 meV covering about ∼ 70 meV of the emission energy) with increasing quantum confinement. These light emitters, grown on a silicon substrate, may exhibit energy-degenerate X and XX energy levels. Furthermore, they emit at the highest detection efficiency window of Si-based single photon detectors. These features render them a promising device platform for the generation of entangled photons in the time-reordering scheme.arXiv:1412.4520v7 [cond-mat.mes-hall]

The multiexciton properties of extrinsic centers from AlGaAs layers on Ge and Si substrates are addressed. The two photon cascade is found both in steady state and in time resolved experiments. Polarization analysis of the photoluminescence provides clearcut attribution to neutral biexciton complexes. Our findings demonstrate the prospect of exploiting extrinsic centers for generating entangled photon pairs on a Si based device.

We investigate the conduction mechanisms of nitronyl-nitroxide molecular radicals, as useful for the creation of nanoscopic molecular spintronic devices, finding that it does not correspond to standard Mott behaviour, as previously postulated. We provide a complete investigation using transport measurements, low-energy, sub-THz spectroscopy and introducing differently-substituted phenyl appendages. We show that a non-trivial surface-charge limited regime is present in addition to the standard low-voltage ohmic conductance. Scaling analysis allows determining all the main transport parameters for the compounds, and highlights the presence of charge trapping effects. Comparison among the different compounds shows the relevance of intermolecular stacking between the aromatic ring of the phenyl appendix and the NIT motif in the creation of useful electron transport channels. The importance of intermolecular pathways is further highlighted by electronic structure calculations, which clarify the nature of the electronic channels and their effect on the Mott character of the compounds.