2,274 research outputs found
Measurement of the Difference between the Dynamic NMR and Static Susceptibilites of Superfluid 3He-B Using an rf-Biased Superconducting Quantum-Interference Device
The temperature-dependent susceptiblity of superfluid 3He-B has been measured both statically and via a pulse technique in a field of 309 G using an rf-biased superconducting quantum-interference device (SQUID). In the pressure range 26.5 to 18 bar, the dynamic NMR susceptiblity agrees qualitatively with the theoretical weak-coupling predictions for the Balian-Werthamer state. However, the static susceptiblity, measured using the same rf-biased SQUID and detection system, is significantly smaller thatn the dynamic susceptibility
Positive Current Correlations Associated with Super-Poissonian Shot Noise
We report on shot noise cross spectrum measurements in a beam splitter configuration. Electrons tunneling through potential barriers are incident on a beam splitter and scattered into two separate channels. Such a partition process introduces correlations between the fluctuations of the two currents. Our work has confirmed that the generally expected negative correlations resulted from sub-Poissonian electron sources. More interestingly, positive cross correlations associated with barriers exhibiting super-Poissonian shot noise have also been observed. We have found that both positive and negative correlations can be related to the noise properties of the electron source
Full shot noise in mesoscopic tunnel barriers
We report shot noise measurements performed in mesoscopic tunnel barriers fabricated in a GaAs∕AlGaAs heterostructure. Two sets of tunnel barriers of different size are used in the study. All large size samples and some of the small size samples show a nonlinear dependence of shot noise on tunneling current due to localized states inside the barriers. Both suppression and enhancement of shot noise have been observed. Some small size barriers, however, exhibit the shot noise behavior of an ideal tunnel barrier over a wide range of barrier transmission coefficients, tunneling currents, and bias voltages
Anomalous Conductance Distribution in Quasi-One-Dimensional Gold Wires: Possible Violation of the One-Parameter Scaling Hypothesis
We report measurements of conductance distribution in a set of quasi-one-dimensional gold wires. The distribution includes the second cumulant or the variance which describes the universal conductance fluctuations, and the third cumulant which denotes the leading deviation. We have observed an asymmetric contribution—or, a nonvanishing third cumulant—contrary to the expectation for quasi-one-dimensional systems in the noninteracting theories in the one-parameter scaling framework, which include the perturbative diagrammatic calculations and the random matrix theory
Mohanty and Webb Reply
A Reply to the Comment by V. I. Fal\u27ko et al
High-Field Measurements of Electron Decoherence Time in Metallic Nanowires: Switching off Magnetic Impurity Spins
We report low-temperature measurements of electron decoherence time in a series of pure gold wires, 18 nm thick and 30 nm wide. At fields up to 15 T, large enough to polarize any concentration of magnetic impurity spins, conductance fluctuation measurements show almost no temperature dependence of the decoherence time below 300 mK, both in the correlation field for interference and the root-mean-square value of the fluctuations. Combined with previous low-field weak localization measurements on samples from similar material, our experiment suggests that the ubiquitous saturation of decoherence time in these samples is not due to any mechanism based on magnetic impurity spins
Coherent control of nanomagnet dynamics via ultrafast spin torque pulses
The magnetization orientation of a nanoscale ferromagnet can be manipulated
using an electric current via the spin transfer effect. Time domain
measurements of nanopillar devices at low temperatures have directly shown that
magnetization dynamics and reversal occur coherently over a timescale of
nanoseconds. By adjusting the shape of a spin torque waveform over a timescale
comparable to the free precession period (100-400 ps), control of the
magnetization dynamics in nanopillar devices should be possible. Here we report
coherent control of the free layer magnetization in nanopillar devices using a
pair of current pulses as narrow as 30 ps with adjustable amplitudes and delay.
We show that the switching probability can be tuned over a broad range by
timing the current pulses with the underlying free-precession orbits, and that
the magnetization evolution remains coherent for more than 1 ns even at room
temperature. Furthermore, we can selectively induce transitions along
free-precession orbits and thereby manipulate the free magnetic moment motion.
We expect this technique will be adopted for further elucidating the dynamics
and dissipation processes in nanomagnets, and will provide an alternative for
spin torque driven spintronic devices, such as resonantly pumping microwave
oscillators, and ultimately, for efficient reversal of memory bits in magnetic
random access memory (MRAM).Comment: 4 pages, 3 figures, submitted to Nature Physic
Single-Electron Charging Effects in Insulating Wires
We present measurements of the transport properties of 0.75-μm-long, narrow, insulating indium oxide wires and rings. These devices have no apparent tunnel barriers, yet they exhibit effects similar to those found in series arrays of very small-capacitance tunnel junctions: highly nonlinear I-V characteristics and a zero-bias conductance which is periodic in a voltage applied by means of a lateral gate. These effects are due to the influence of single-electron charging on transport through localized states in the insulating regime
Experimental study of nonlinear conductance in small metallic samples
We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample
Temperature dependent asymmetry of the nonlocal spin-injection resistance: evidence for spin non-conserving interface scattering
We report nonlocal spin injection and detection experiments on mesoscopic
Co-Al2O3-Cu spin valves. We have observed a temperature dependent asymmetry in
the nonlocal resistance between parallel and antiparallel configurations of the
magnetic injector and detector. This strongly supports the existence of a
nonequilibrium resistance that depends on the relative orientation of the
detector magnetization and the nonequilibrium magnetization in the normal metal
providing evidence for increasing interface spin scattering with temperature.Comment: 5 pages, 4 figures, accepted for publication in PRL, minor
corrections (affiliation, acknowledgements, typo
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