We have studied field- and current-driven domain-wall (DW) creep motion in a perpendicularly magnetized Co/Pt multilayer wire by real-time Kerr microscopy. The application of a dc current of density of approximately < 10(7) A/cm2 assisted only the DW creeping under field in the same direction as the electron flow, a signature of spin-transfer torque effects. We develop a model dealing with both bidirectional spin-transfer effects and Joule heating, with the same dynamical exponent mu=1/4 for both field- and current-driven creep, and use it to quantify the spin-transfer efficiency as 3.6+/-0.6 Oe cm2/MA in our wires, confirming the significant nonadiabatic contribution to the spin torque.

Superconducting nanowire single photon detectors (SNSPDs) are a key enabling technology for optical quantum information science. In this paper we demonstrate a SNSPD fabricated on lithium niobate, an important material for high speed integrated photonic circuits. We report a system detection efficiency of 0.15% at a 1 kHz dark count rate with a maximum of ~1% close to the critical current at 1550 nm wavelength for a parallel wire SNSPD with front side illumination. There is clear scope for improving on this performance with further materials optimization. Detector integration with a lithium niobate optical waveguide is simulated, demonstrating the potential for high single photon detection efficiency in an integrated quantum optic circuit.

The device physics of parallel-wire superconducting nanowire single photon detectors is based on a cascade process. Using nano-optical techniques and a parallel wire device with spatially-separate pixels we explicitly demonstrate the single-and multi-photon triggering regimes. We develop a model for describing efficiency of a detector operating in the arm-trigger regime. We investigate the timing response of the detector when illuminating a single pixel and two pixels. We see a change in the active area of the detector between the two regimes and find the two-pixel trigger regime to have a faster timing response than the one-pixel regime.

Investigation of artificial domains realized by local gallium focused ion-beam modification of Pt ∕ Co ∕ Pt trilayer structures J. Appl. Phys. 99, 08C504 (2006); 10.1063/1.2159393 Anomalous Hall-effect measurement study on Co ∕ Pt nanosized dot J. Appl. Phys. 97, 10J713 (2005); 10.1063/1.1859971Exchange-biased spin valves with perpendicular magnetic anisotropy based on (Co/Pt) multilayers

Perpendicular spin transfer torque magnetic random access memories with high spin torque efficiency and thermal stability for embedded applications (invited)