Angular Conductance Resonances of Quantum Dots Non-Collinearly Coupled to Ferromagnetic Leads

The zero bias conductance of quantum dots coupled to ferromagnetic leads is investigated. In the strong coupling regime, it is found that the conductance is a non-monotonic function of the angle between the magnetisation directions in the two contacts. This behaviour is an effect of the presence of the leads which induces an angle dependent spin split of the quantum dot states, and spin flip transitions between the quantum dot states whenever the magnetisation directions of the leads are non-collinear which enhances the current density at the chemical potential. In the weak coupling regime, the system reverts to normal spin valve character.Comment: 4 pages, 4 figures. Europhysics Letters (accepted

The X-ray and radio emission from SN 2002ap: The importance of Compton scattering

The radio and X-ray observations of the Type Ic supernova SN 2002ap are modeled. We find that inverse Compton cooling by photospheric photons explains the observed steep radio spectrum, and also the X-ray flux observed by XMM. Thermal emission from the shock is insufficient to explain the X-ray flux. The radio emitting region expands with a velocity of, roughly, 70,000 km/s. From the ratio of X-ray to radio emission we find that the energy densities of magnetic fields and relativistic electrons are close to equipartion.Comment: 15 pages, 2 figures, ApJ accepte

Detection of spin reversal and nutations through current measurements

The dynamics of a single spin embedded in a the tunnel junction between ferromagnetic contacts is strongly affected by the exchange coupling to the tunneling electrons. Moment reversal of the local spin induced by the bias voltage across the junction is shown to have a measurable effect on the tunneling current. Furthermore, the frequency of a harmonic bias voltage is picked up by the local spin dynamics and transferred back to the current generating a double frequency component.Comment: 5 pages, 5 figures; published version (with minor corrections

Responses of ectomycorrhizal fungi to changes in carbon and nutrient availability

Ectomycorrhizal (ECM) fungi may receive 20% of the total C fixed by their host plants and are essential components of host nutrient acquisition. As a consequence of the vast physiological diversity that exists among ECM fungi, changes in community structure may potentially alter C and nutrient allocation and turnover within forest ecosystems. Effects of atmospheric CO2 enrichment and balanced nutrient addition on the community structure of ECM fungi were investigated. Significant effects of elevated CO2 , as well as elevated nutrient levels were found. Daily nutrient additions for 10 years did not cause reductions in the density of ECM roots or the degree of root colonisation, in contrast to other studies. Some species became more common due to nutrient additions; Cenococcum geophilum, Amphinema byssoides, Tylospora fibrillosa, tomentelloid species, and others, Piloderma byssinum and P. croceum, became less common. High variability among samples made individual species responses difficult to distinguish. Data suggest that the same species may respond similarly to both elevated CO2 and nutrient additions. In laboratory experiments, CO2 enrichment increased the production of extraradical mycelium by Hebeloma crustuliniforme, increasing mycelial spread and root colonisation. Under field conditions such a response could enable species to increase in abundance. The natural abundance of the stable isotope 13 C in fruitbodies can be used as a tool to distinguish between the two functional groups ECM and saprotrophic fungi. However, some caution is neccesary in the interpretation since values overlap between the two functional groups. The 13 C values can also be used to reveal the host-origin of carbon in mycorrhizal fungi in mixed forests. Generalist fungi, which can be associated with several different tree species, were found to receive most of their C from overstorey trees, as indicated by their high d 13 C values. This implies that large trees which are able to fix more C potentially subsidise smaller trees via a common ECM mycelial netwo

Formation of pure two-electron triplet states in weakly coupled quantum dots attached to ferromagnetic leads

Weakly coupled quantum dots in the Pauli spin blockade regime are considered with respect to spin-dependent transport. By attaching one half-metallic and one non-magnetic lead, the Pauli spin blockade if formed by a pure triplet state with spin moment $S_z=1$ or -1. Furthermore, additional spin blockade regimes emerge because of full occupation in states with opposite spin to that of the half-metallic lead.Comment: 6 pages, 2 figures, 1 table, minor changes to appear as publishe

Spin Inelastic Electron Tunneling Spectroscopy on Local Magnetic Moment Embedded in Josephson Junction

Recent experimental conductance measurements performed on paramagnetic molecular adsorbates on a superconducting surface, using superconducting scanning tunneling microscopy techniques, are theoretically investigated. For low temperatures, we demonstrate that tunneling current assisted excitations of the local magnetic moment cannot occur for voltage biases smaller than the superconducting gap of the scanning tunneling microscope. The magnetic moment is only excited for voltages corresponding to the sum of the superconducting gap and the spin excitation energies. In excellent agreement with experiment, we show that pumping into higher excitations give additional current signatures by accumulation of density in the lower ones. Using external magnetic fields, we Zeeman split possible degeneracy and thereby resolve all excitations comprised in the magnetic moment.Comment: 6 pages, 4 figures, submitte