Magnetic Field Geometry of the Broad Line Radio Galaxy 3C111

Very Long Baseline Polarimetric observations of the Broad Line Radio galaxy 3C111 performed in July and September of 1996 at 8 and 43 GHz reveal rapidly evolving parsec-scale radio structure after a large millimetre outburst. The B-field geometry is not simple. We present a first analysis of possible Faraday and optical depth effects based on a comparison of the polarization images for the two frequencies.Comment: 4 pages, 4 figures, Proceedings of conference "The Physics of Relativistic Jets in the Chandra and XMM Era", eds. G. Brunetti, D.E. Harris, R.M. Sambruna, and G. Setti, submitted to New Astronomy Revie

Cavity-induced slow gain recovery in pump-probe experiments of quantum cascade lasers

We show that the Fabry-P´erot cavity dynamics of quantum cascade lasers (QCLs) play an important role in the gain recovery observed in a pump-probe experiment. Due to the residual pump power in the cavity after the pump pulse is reflected from the facet, the probed gain recovers at a slower rate

Scattering in InAs/GaSb Coupled Quantum Wells as a Probe of Higher Order Subband Hybridisation

We have performed a detailed investigation into the inter-subband scattering within InAs/GaSb coupled quantum wells in the electron dominated regime. By considering the carrier mobilities and the quantum lifetime as a function of carrier density, we find that the occupation of higher order electron-like subbands are inhibited by anticrossing with the hole subbands. We also find that, by applying a gate bias to the GaSb layer, we are able to move the electron-hole anticrossing point in energy, modulating the electron-like states that should be localised within the InAs layer

Suppression of Dynamically Induced Stochastic Magnetic Behaviour through Materials Engineering

tochastic behavior fundamentally limits the performance and reliability of nanomagnetic devices. Typically, stochastic behavior is assumed to be the result of simple thermal activation, but it may also be “dynamically induced,” i.e., a direct result of the spatial and temporal complexity of magnetization dynamics. Here, we show how materials engineering can be used to comprehensively suppress dynamically induced stochasticity. Using the dynamics of magnetic domain walls in Ni80Fe20 nanowires as a case study, we show how manipulation of the Gilbert damping constant via doping with the rare-earth-element terbium dramatically simplifies domain-wall dynamics. This allows us to obtain quasi-deterministic behaviors from systems that nominally exhibit exceptionally high levels of stochasticity

Shot Noise in Mesoscopic Transport Through Localised States

We show that shot noise can be used for studies of hopping and resonant tunnelling between localised electron states. In hopping via several states, shot noise is seen to be suppressed compared with its classical Poisson value $S_I=2eI$ ($I$ is the average current) and the suppression depends on the distribution of the barriers between the localised states. In resonant tunnelling through a single impurity an enhancement of shot noise is observed. It has been established, both theoretically and experimentally, that a considerable increase of noise occurs due to Coulomb interaction between two resonant tunnelling channels.Comment: 7 pages, 5 figures; Proceedings of the 10th Conference on Hopping and Related Phenomena (Trieste 2003); requires Wiley style files (included

Tunneling Between Two-Dimensional Electron Gases in a Strong Magnetic Field

We have measured the tunneling between two two-dimensional electron gases at high magnetic fields $B$, when the carrier densities of the two electron layers are matched. For filling factors $\nu<1$, there is a gap in the current-voltage characteristics centered about $V=0$, followed by a tunneling peak at $\sim 6$~mV. Both features have been observed before and have been attributed to electron-electron interactions within a layer. We have measured high field tunneling peak positions and fitted gap parameters that are proportional to $B$, and independent of the carrier densities of the two layers. This suggests a different origin for the gap to that proposed by current theories, which predict a $\sqrt{B}$ dependence.Comment: 9 pages, cond-mat/yymmnn

Frequency tunability and spectral control in terahertz quantum cascade lasers with phase-adjusted finite-defect-site photonic lattices

We report on the effect of finite-defect-site photonic lattices (PLs) on the spectral emission of terahertz frequency quantum cascade lasers, both theoretically and experimentally. A central π-phase adjusted defect incorporated in the PL is shown to favor emission selectively within the photonic bandgap. The effect of the duty cycle and the longitudinal position of such PLs is investigated, and used to demonstrate three distinct spectral behaviors: single mode emission from devices in the range 2.2−5 THz, with a side-mode suppression ratio of 40 dB and exhibiting continuous frequency tuning over >8 GHz; discrete tuning between two engineered emission modes separated by ~40 GHz; and, multiple-mode emission with an engineered frequency spacing between emission lines