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1.
Phys Rev E ; 102(1-1): 012312, 2020 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-32794998

RESUMEN

We use an artificial neural network to analyze asymmetric noisy random telegraph signals, and extract underlying transition rates. We demonstrate that a long short-term memory neural network can outperform other methods, particularly for noisy signals and measurements with limited bandwidths. Our technique gives reliable results as the signal-to-noise ratio approaches one, and over a wide range of underlying transition rates. We apply our method to random telegraph signals generated by quasiparticle poisoning in a superconducting double dot, allowing us to extend our measurement of quasiparticle dynamics to new temperature regimes.

2.
Phys Rev Lett ; 117(13): 133602, 2016 Sep 23.
Artículo en Inglés | MEDLINE | ID: mdl-27715091

RESUMEN

An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wave vector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.

3.
Nano Lett ; 15(7): 4622-7, 2015 Jul 08.
Artículo en Inglés | MEDLINE | ID: mdl-26047255

RESUMEN

We report the dispersive readout of the spin state of a double quantum dot formed at the corner states of a silicon nanowire field-effect transistor. Two face-to-face top-gate electrodes allow us to independently tune the charge occupation of the quantum dot system down to the few-electron limit. We measure the charge stability of the double quantum dot in DC transport as well as dispersively via in situ gate-based radio frequency reflectometry, where one top-gate electrode is connected to a resonator. The latter removes the need for external charge sensors in quantum computing architectures and provides a compact way to readout the dispersive shift caused by changes in the quantum capacitance during inter-dot charge transitions. Here, we observe Pauli spin-blockade in the high-frequency response of the circuit at finite magnetic fields between singlet and triplet states. The blockade is lifted at higher magnetic fields when intra-dot triplet states become the ground state configuration. A line shape analysis of the dispersive phase shift reveals furthermore an intra-dot valley-orbit splitting Δvo of 145 µeV. Our results open up the possibility to operate compact complementary metal-oxide semiconductor (CMOS) technology as a singlet-triplet qubit and make split-gate silicon nanowire architectures an ideal candidate for the study of spin dynamics.

4.
Nat Commun ; 6: 6730, 2015 Mar 31.
Artículo en Inglés | MEDLINE | ID: mdl-25823949

RESUMEN

Recently discovered relativistic spin torques induced by a lateral current at a ferromagnet/paramagnet interface are a candidate spintronic technology for a new generation of electrically controlled magnetic memory devices. The focus of our work is to experimentally disentangle the perceived two model physical mechanisms of the relativistic spin torques, one driven by the spin-Hall effect and the other one by the inverse spin-galvanic effect. Here, we show a vector analysis of the torques in a prepared epitaxial transition-metal ferromagnet/semiconductor-paramagnet single-crystal structure by means of the all-electrical ferromagnetic resonance technique. By choice of our structure in which the semiconductor paramagnet has a Dresselhaus crystal inversion asymmetry, the system is favourable for separating the torques due to the inverse spin-galvanic effect and spin-Hall effect mechanisms into the field-like and antidamping-like components, respectively. Since they contribute to distinct symmetry torque components, the two microscopic mechanisms do not compete but complement each other in our system.

5.
Nat Commun ; 6: 6084, 2015 Jan 20.
Artículo en Inglés | MEDLINE | ID: mdl-25600002

RESUMEN

Quantum computation requires a qubit-specific measurement capability to readout the final state of individual qubits. Promising solid-state architectures use external readout electrometers but these can be replaced by a more compact readout element, an in situ gate sensor. Gate-sensing couples the qubit to a resonant circuit via a gate and probes the qubit's radiofrequency polarizability. Here we investigate the ultimate performance of such a resonant readout scheme and the noise sources that limit its operation. We find a charge sensitivity of 37 µe Hz(-1/2), the best value reported for this technique, using the example of a gate sensor strongly coupled to a double quantum dot at the corner states of a silicon nanowire transistor. We discuss the experimental factors limiting gate detection and highlight ways to optimize its sensitivity. In total, resonant gate-based readout has advantages over external electrometers both in terms of reduction of circuit elements as well as absolute charge sensitivity.

6.
Nat Nanotechnol ; 9(3): 211-7, 2014 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-24584275

RESUMEN

Magnetization switching at the interface between ferromagnetic and paramagnetic metals, controlled by current-induced torques, could be exploited in magnetic memory technologies. Compelling questions arise regarding the role played in the switching by the spin Hall effect in the paramagnet and by the spin-orbit torque originating from the broken inversion symmetry at the interface. Of particular importance are the antidamping components of these current-induced torques acting against the equilibrium-restoring Gilbert damping of the magnetization dynamics. Here, we report the observation of an antidamping spin-orbit torque that stems from the Berry curvature, in analogy to the origin of the intrinsic spin Hall effect. We chose the ferromagnetic semiconductor (Ga,Mn)As as a material system because its crystal inversion asymmetry allows us to measure bare ferromagnetic films, rather than ferromagnetic-paramagnetic heterostructures, eliminating by design any spin Hall effect contribution. We provide an intuitive picture of the Berry curvature origin of this antidamping spin-orbit torque as well as its microscopic modelling. We expect the Berry curvature spin-orbit torque to be of comparable strength to the spin-Hall-effect-driven antidamping torque in ferromagnets interfaced with paramagnets with strong intrinsic spin Hall effect.

7.
Nat Mater ; 10(9): 660-4, 2011 Jul 03.
Artículo en Inglés | MEDLINE | ID: mdl-21725322

RESUMEN

Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of damping in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation; the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.

8.
Nat Nanotechnol ; 6(7): 413-7, 2011 May 22.
Artículo en Inglés | MEDLINE | ID: mdl-21602814

RESUMEN

Ferromagnetic resonance is the most widely used technique for characterizing ferromagnetic materials. However, its use is generally restricted to wafer-scale samples or specific micro-magnetic devices, such as spin valves, which have a spatially varying magnetization profile and where ferromagnetic resonance can be induced by an alternating current owing to angular momentum transfer. Here we introduce a form of ferromagnetic resonance in which an electric current oscillating at microwave frequencies is used to create an effective magnetic field in the magnetic material being probed, which makes it possible to characterize individual nanoscale samples with uniform magnetization profiles. The technique takes advantage of the microscopic non-collinearity of individual electron spins arising from spin-orbit coupling and bulk or structural inversion asymmetry in the band structure of the sample. We characterize lithographically patterned (Ga,Mn)As and (Ga,Mn)(As,P) nanoscale bars, including broadband measurements of resonant damping as a function of frequency, and measurements of anisotropy as a function of bar width and strain. In addition, vector magnetometry on the driving fields reveals contributions with the symmetry of both the Dresselhaus and Rashba spin-orbit interactions.

9.
Rev Sci Instrum ; 80(11): 114705, 2009 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-19947749

RESUMEN

The authors demonstrate readout of electrically detected magnetic resonance at radio frequencies by means of a LCR tank circuit. Applied to a silicon field-effect transistor at millikelvin temperatures, this method shows a 25-fold increased signal-to-noise ratio of the conduction band electron spin resonance and a higher operational bandwidth of >300 kHz compared to the kilohertz bandwidth of conventional readout techniques. This increase in temporal resolution provides a method for future direct observations of spin dynamics in the electrical device characteristics.

10.
Nanotechnology ; 19(19): 195402, 2008 May 14.
Artículo en Inglés | MEDLINE | ID: mdl-21825715

RESUMEN

We present low temperature charge sensing measurements of nanoscale phosphorus-implanted double dots in silicon. The implanted phosphorus forms two 50 nm diameter islands with source and drain leads, which are separated from each other by undoped silicon tunnel barriers. Occupancy of the dots is controlled by surface gates and monitored using an aluminium single-electron transistor which is capacitively coupled to the dots. We observe a charge stability diagram consistent with the designed many-electron double-dot system and this agrees well with capacitance modelling of the structure. We discuss the significance of these results to the realization of smaller devices which may be used as charge or spin qubits.

11.
Nanotechnology ; 19(26): 265201, 2008 Jul 02.
Artículo en Inglés | MEDLINE | ID: mdl-21828673

RESUMEN

We report a detailed study of low-temperature (mK) transport properties of a silicon double-dot system fabricated by phosphorous ion implantation. The device under study consists of two phosphorous nanoscale islands doped to above the metal-insulator transition, separated from each other and the source and drain reservoirs by nominally undoped (intrinsic) silicon tunnel barriers. Metallic control gates, together with an Al-AlO(x) single-electron transistor (SET), were positioned on the substrate surface, capacitively coupled to the buried dots. The individual double-dot charge states were probed using source-drain bias spectroscopy combined with non-invasive SET charge sensing. The system was measured in linear (source-drain DC bias V(SD) = 0) and non-linear (V(SD) ≠ 0) regimes, allowing calculations of the relevant capacitances. Simultaneous detection using both SET sensing and source-drain current measurements was demonstrated, providing a valuable combination for the analysis of the system. Evolution of the triple points with applied bias was observed using both charge and current sensing. Coulomb diamonds, showing the interplay between the Coulomb charging effects of the two dots, were measured using simultaneous detection and compared with numerical simulations.

12.
Phys Rev Lett ; 97(10): 106603, 2006 Sep 08.
Artículo en Inglés | MEDLINE | ID: mdl-17025837

RESUMEN

We present radio-frequency measurements on a single-Cooper-pair-transistor in which individual quasiparticle poisoning events were observed with microsecond temporal resolution. Thermal activation of the quasiparticle dynamics is investigated, and consequently, we are able to determine energetics of the poisoning and unpoisoning processes. In particular, we are able to assign an effective quasiparticle temperature to parametrize the poisoning rate.

13.
Phys Rev Lett ; 97(8): 086602, 2006 Aug 25.
Artículo en Inglés | MEDLINE | ID: mdl-17026322

RESUMEN

We investigate the effect of Zeeman splitting on quasiparticle transport in normal-superconducting-normal (NSN) aluminum single-electron transistors (SETs). In the above-gap transport, the interplay of Coulomb blockade and Zeeman splitting leads to spin-dependence of the sequential tunneling. This creates regimes where either one or both spin species can tunnel onto or off the island. At lower biases, spin-dependence of the single quasiparticle state is studied, and operation of the device as a bipolar spin filter is suggested.

14.
J Phys Chem B ; 110(13): 6891-8, 2006 Apr 06.
Artículo en Inglés | MEDLINE | ID: mdl-16570999

RESUMEN

The effect of deposition temperature on the photophysical properties of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and N,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (Me-PTCDI) films is investigated with steady-state and time-resolved spectroscopy. Atomic force microscopy (AFM) images of the film surfaces show an increase in the dimensions of crystallites with substrate temperature, culminating in the formation of elongated crystallites on substrates held close to the sublimation temperature. In contrast, despite an improvement in the crystal quality, X-ray diffraction (XRD) studies indicate that the substrate temperature has a negligible effect on the molecular orientation; the PTCDA and Me-PTCDI molecules align parallel and tilted to the substrate surface, respectively. Both materials exhibit characteristic absorption, due to mixing between charge-transfer and Frenkel species, and broad structureless photoluminescence. Growth at elevated temperatures gives rise to increased low-energy absorption, attributed to the formation of charge-transfer species, and enhanced blue-shifted emission, although the effects are less pronounced for Me-PTCDI. Time-correlated single-photon counting data indicate that the enhancement coincides with a lengthening of the fluorescence decays, over the whole emission spectrum.

15.
Plant Dis ; 83(12): 1129-1136, 1999 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-30841137

RESUMEN

A baiting bioassay was developed to detect species of Phytophthora, i.e., those typically associated with ornamental crops, in container mixes that are used routinely in producing container-grown landscape plants. Both fresh and air-dried subsamples of container mixes were baited to improve detection of species that persist as dormant propagules. Leaf disks of Camellia japonica detected Phytophthora spp. most frequently and consistently, but intact needles of shore juniper also were effective baits and less likely to become contaminated. Phytophthora spp. were detected at baiting durations of 24, 48, and 72 h; both detection and contamination were greatest at 72 h. To minimize problems from contamination and maximize detection, camellia leaf disks and shore juniper needles were used simultaneously; half of the baits were removed at 24 h and the other half were removed at 72 h. Baiting at temperatures of 15, 20, and 25°C did not have a dramatic effect on detection; however, Phytophthora spp. occasionally were detected more frequently at 20 and 25°C than at 15°C. Both camellia leaf disks and shore juniper needles were colonized readily by zoospores of P. cinnamomi, P. nicotianae (= P. parasitica), P. cryptogea, and P. citricola but were not colonized as readily by zoospores of P. cactorum. Disks from leaves of C. sasanqua and six cultivars of C. japonica were effective as baits; however, some differences among camellia types occurred. P. cinnamomi, P. nicotianae, P. citricola, P. citrophthora, P. cryptogea, and P. cactorum have been detected in naturally infested container mixes using this baiting bioassay.

16.
Anaesthesia ; 52(4): 359-63, 1997 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-9135190

RESUMEN

We report the case of a 14-year-old girl who deliberately ingested 8-9 g of dapsone and presented with severe methaemoglobinaemia and altered mental status. Prompt treatment with repeated doses of methylene blue and organ support brought about control of the methaemoglobinaemia and averted organ failure.


Asunto(s)
Dapsona/envenenamiento , Leprostáticos/envenenamiento , Metahemoglobinemia/inducido químicamente , Adolescente , Antídotos/uso terapéutico , Bilirrubina/sangre , Cuidados Críticos/métodos , Femenino , Humanos , L-Lactato Deshidrogenasa/sangre , Metahemoglobinemia/terapia , Azul de Metileno/uso terapéutico , Respiración Artificial
18.
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