arXiv subjects

F. Wu

Publications and source records attributed to F. Wu.

45 records · Page 3Linked to original sources

arXiv2008

Highly sensitive and broadband carbon nanotube radio-frequency single-electron transistor

We have investigated radio-frequency single-electron transistor (RF-SET) operation of single-walled carbon nanotube quantum dots in the strong tunneling regime. At 4.2 K and carrier frequency 754.2 MHz, we reach a charge sensitivity of 2.3e-6 e/Hz^(1/2) over a bandwidth of 85 MHz. Our results indicate a gain-bandwidth product of 3.7e13 Hz^(3/2)/e, which is by one order of magnitude better than for typical RF-SETs.

cond-mat.other↗

arXiv2007

Local and Non-local Shot Noise in Multiwalled Carbon Nanotubes

We have investigated shot noise in multiterminal, diffusive multiwalled carbon nanotubes (MWNTs) at 4.2 K over the frequency f = 600 - 850 MHz. Quantitative comparison of our data to semiclassical theory, based on non-equilibrium distribution functions, indicates that a major part of the noise is caused by a non-equilibrium state imposed by the contacts. Our data exhibits non-local shot noise across weakly transmitting contacts while a low-impedance contact eliminates such noise almost fully. We obtain F_{tube}< 0.03 for the intrinsic Fano factor of our MWNTs.

cond-mat.mes-hall↗

arXiv2007

Shot Noise with Interaction Effects in Single Walled Carbon Nanotubes

We have measured shot noise in single walled carbon nanotubes (SWNT) with good contacts at 4.2 K at low frequencies ($f=600 - 850$ MHz). We find a strong modulation of shot noise over the Fabry-Perot pattern; in terms of differential Fano factor the variation ranges over 0.4 - 1.2. The shot noise variation, in combination with differential conductance, is analyzed using two (spin-degenerate) modes with different, energy-dependent transmission coefficients. No power law dependence of shot noise, as expected for Luttinger liquids, was found in our measurements.

cond-mat.mes-hall↗

arXiv2007

Observations of the Askaryan Effect in Ice

We report on the first observations of the Askaryan effect in ice: coherent impulsive radio Cherenkov radiation from the charge asymmetry in an electromagnetic (EM) shower. Such radiation has been observed in silica sand and rock salt, but this is the first direct observation from an EM shower in ice. These measurements are important since the majority of experiments to date that rely on the effect for ultra-high energy neutrino detection are being performed using ice as the target medium. As part of the complete validation process for the Antarctic Impulsive Transient Antenna (ANITA) experiment, we performed an experiment at the Stanford Linear Accelerator Center (SLAC) in June 2006 using a 7.5 metric ton ice target, yielding results fully consistent with theoretical expectations.

hep-ex↗

arXiv2006

Shot noise of a multiwalled carbon nanotube field effect transistor

We have investigated shot noise in a 6-nm-diameter, semiconducting multiwalled carbon nanotube FET at 4.2 K over the frequency range 600 - 950 MHz. We find a transconductance of 3 - 3.5 $μ$S for optimal positive and negative source-drain voltages V. For the gate referred input voltage noise, we obtain 0.2 and 0.3 $μ{V}/ \sqrt{Hz}$ for V>0 and V<0, respectively. As effective charge noise this corresponds to $2-3 \cdot 10^{-5}$ e/$\sqrt{Hz}$.

cond-mat.mes-hall↗

arXiv2006

Constraints on Cosmic Neutrino Fluxes from the ANITA Experiment

We report new limits on cosmic neutrino fluxes from the test flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment, which completed an 18.4 day flight of a prototype long-duration balloon payload, called ANITA-lite, in early 2004. We search for impulsive events that could be associated with ultra-high energy neutrino interactions in the ice, and derive limits that constrain several models for ultra-high energy neutrino fluxes. We rule out the long-standing Z-burst model as the source for the ultra-high energy cosmic rays.

astro-ph↗

arXiv2004

Status of ANITA and ANITA-lite

We describe a new experiment to search for neutrinos with energies above 3 x 10^18 eV based on the observation of short duration radio pulses that are emitted from neutrino-initiated cascades. The primary objective of the ANtarctic Impulse Transient Antenna (ANITA) mission is to measure the flux of Greisen-Zatsepin-Kuzmin (GZK) neutrinos and search for neutrinos from Active Galactic Nuclei (AGN). We present first results obtained from the successful launch of a 2-antenna prototype instrument (called ANITA-lite) that circled Antarctica for 18 days during the 03/04 Antarctic campaign and show preliminary results from attenuation length studies of electromagnetic waves at radio frequencies in Antarctic ice. The ANITA detector is funded by NASA, and the first flight is scheduled for December 2006.

astro-ph↗

arXiv2003

The braking indices in pulsar emission models

Using the method proposed in a previous paper, we calculate pulsar braking indices in the models with torque contributions from both inner and outer accelerating regions, assuming that the interaction between them is negligible. We suggest that it is likely that the inverse Compton scattering induced polar vacuum gap and the outer gap coexist in the pulsar magnetosphere. We include the new near threshold vacuum gap models with curvature-radiation and inverse Compton scattering induced cascades, respectively; and find that these models can well reproduce the measured values of the braking indices.

astro-ph↗

arXiv2003

Ultra High Energy Cosmic Rays: Strangelets? -- Extra dimensions, TeV-scale black holes and strange matter

The conjecture that ultra high energy cosmic rays (UHECRs) are actually strangelets is discussed. Besides the reason that strangelets can do as cosmic rays beyond the GZK-cutoff, another argument to support the conjecture is addressed in this letter via the study of formation of TeV-scale microscopic black holes when UHECRs bombarding bare strange stars. It is proposed that the exotic quark surface of a bare strange star could be an effective astro-laboratory in the investigations of the extra dimensions and of the detection of ultra-high energy neutrino fluxes. The flux of neutrinos (and other point-like particles) with energy >2.3 x 10^{20} eV could be expected to be smaller than 10^{-26} cm^{-2}$ s^{-1} if there are two extra spatial dimensions.

astro-ph↗