Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions

Our previous point-contact Andreev reflection studies of the heavy-fermion superconductor CeCoIn$_5$ using Au tips have shown two clear features: reduced Andreev signal and asymmetric background conductance [1]. To explore their physical origins, we have extended our measurements to point-contact junctions between single crystalline heavy-fermion metals and superconducting Nb tips. Differential conductance spectra are taken on junctions with three heavy-fermion metals, CeCoIn$_5$, CeRhIn$_5$, and YbAl$_3$, each with different electron mass. In contrast with Au/CeCoIn$_5$ junctions, Andreev signal is not reduced and no dependence on effective mass is observed. A possible explanation based on a two-fluid picture for heavy fermions is proposed. [1] W. K. Park et al., Phys. Rev. B 72 052509 (2005); W. K. Park et al., Proc. SPIE-Int. Soc. Opt. Eng. 5932 59321Q (2005); W. K. Park et al., Physica C (in press) (cond-mat/0606535).Comment: 2 pages, 2 figures, submitted to the SCES conference, Houston, Texas, USA, May 13-18, 200

Separable states to distribute entanglement

It was shown that two distant particles can be entangled by sending a third particle never entangled with the other two [T. S. Cubitt et al., Phys. Rev. Lett. 91, 037902 (2003)]. In this paper, we investigate a class of three-qubit separable states to distribute entanglement by the same way, and calculate the maximal amount of entanglement which two particles of separable states in the class can have after applying the way.Comment: 4 pages, no figures, Revised argumen

Extreme waves generated by Typhoon Bolaven (201215) in Southern Korean waters

Unusual extreme waves were generated by Typhoon Bolaven (201215) in the Southern Korean Waters\ud (SKW) and gave destructive damages to the breakwaters of Seogwipo Harbor at Jeju Island. The waves were far\ud exceeding the design wave height (Hs50yrs 9.3m) and their duration was 14hours. The duration is a very significant\ud factor as much as the design wave height for breakwater armor stability in terms of cumulative damages. A significant\ud increase in strong typhoon intensity and duration in North West Pacific (NWP) due to global warming has been reported\ud and also in landfall typhoons on Korea/Japan in a recent decade. The frequency of typhoon passed SKW region had an\ud inter-annual and also a decadal variation and decreased in recent years, but several strong typhoons were occurred.\ud Bolaven was affected by high pressure distribution located above the warm eddy region to track toward NNW rather\ud than NE as usual in August. The extreme waves were analyzed with respect to typhoon genesis, evolution of the waves\ud through extensive measured data and model simulation. Numerical models of TC96 for the wind fields and WAM4.5.2\ud for the waves were used after calibration with measured data and correction of Cd in wave growth term. They produced\ud reasonably good results. It was found that the extreme waves were evolved by combination of distant large swell and\ud strong wind seas generated by consistent strong winds from front right quadrant of typhoon track for such a long time.\ud The variation of those waves was relatively small as 1-2m, which might be due to limitation of wave growth for\ud U>30m/s and bottom energy dissipation of long period waves in the region. It is essential to hindcast accurately the\ud extreme waves for design of the breakwaters and also for assessment of coastal flooding and coastal erosion in a\ud warming climate

Enhancement of electrical properties in Al-doped ZnO films by tuning dc bias voltage during radio frequency magnetron sputtering

Al-doped ZnO (AZO) thin films were deposited at room temperature on glass substrates by rf magnetron sputtering with simultaneous dc bias through an external inductor coil. The deposition rates of AZO films deposited using simultaneous rf and dc power along with an inductor coil were 20 higher than those deposited using only rf power. The effects of simultaneous rf and dc bias voltage during the deposition of AZO films were investigated in terms of their resistivity and compressive stress. It was observed that the AZO films deposited at 120 W rf power with 600 μH inductor coil exhibit the lowest resistivity of 6.71 à 10-4 Ïṡcm. © 2012 Elsevier B.V. All rights reserved

Bistable Organic Memory Device with Gold Nanoparticles Embedded in a Conducting Poly(N-vinylcarbazole) Colloids Hybrid

We report on the nonvolatile memory characteristics of a bistable organic memory (BOM) device with Au nanopartides (NPs) embedded in a conducting poly(N-vinylcarbazole) (PVK) colloids hybrid layer deposited on flexible poly(ethylenete-rephthalate) (PET) substrates. Transmission electron microscopy (TEM) images show the Au nanoparticles distributed isotropically around the surface of a PVK colloid. The average induced charge on Au nanoparticles, estimated using the C-V hysteresis curve, was large, as much as 5 holes/NP at a sweeping voltage of +/-3 V. The maximum ON/OFF ratio of the current bistability in the BOM devices was as large as 1 x 10(5). The cycling endurance tests of the ON/OFF switching exhibited a high endurance of above 1.5 x 10(5) cycles, and a high ON/OFF ratio of similar to 10(5) could be achieved consistently even after quite a long retention time of more than 1 x 10(6) s. To clarify the memory mechanism of the hole-mediated bistable organic memory device, the interactions between Au nanoparticles and poly(N-vinylcarbazole) colloids was studied by estimating the density of states and projected density of state calculations using density functional theory. Au atom interactions with a PVK unit decreased the band gap by 2.96 eV with the new induced gap states at 5.11 eV (HOMO, E(0)) and LUMO 4.30 eV and relaxed the HOMO level by 0.5 eV (E(1)). E(1) at similar to 6.2 eV is very close to the pristine HOMO, and thus the trapped hole in E(1) could move to the HOMO of pristine PVK From the experimental data and theoretical calculation, it was revealed that a low-conductivity state resulted from a hole trapping at E(o) and E(1) states and subsequent hole transportation through Fowler-Nordheim tunneling from E(1) state to Au NPs and/or interface trap states leads to a high conductivity state

Optical band edge shift of anatase cobalt-doped titanium dioxide

We report on the optical properties of magnetic cobalt-doped anatase phase titanium dioxide Ti_{1-x}Co_{x}O_{2-d} films for low doping concentrations, 0 <= x <= 0.02, in the spectral range 0.2 to 5 eV. For well oxygenated films (d << 1) the optical conductivity is characterized by an absence of optical absorption below an onset of interband transitions at 3.6 eV and a blue shift of the optical band edge with increasing Co concentration. The absence of below band gap absorption is inconsistent with theoretical models which contain midgap magnetic impurity bands and suggests that strong on-site Coulomb interactions shift the O-band to Co-level optical transitions to energies above the gap.Comment: 5 pages, 4 figures, 1 table; Version 2 - major content revisio

The Effect of Splayed Pins on Vortex Creep and Critical Currents

We study the effects of splayed columnar pins on the vortex motion using realistic London Langevin simulations. At low currents vortex creep is strongly suppressed, whereas the critical current j_c is enhanced only moderately. Splaying the pins generates an increasing energy barrier against vortex hopping, and leads to the forced entanglement of vortices, both of which suppress creep efficiently. On the other hand splaying enhances kink nucleation and introduces intersecting pins, which cut off the energy barriers. Thus the j_c enhancement is strongly parameter sensitive. We also characterize the angle dependence of j_c, and the effect of different splaying geometries.Comment: 4 figure

Imaging of Spin Dynamics in Closure Domain and Vortex Structures

Time-resolved Kerr microscopy is used to study the excitations of individual micron- scale ferromagnetic thin film elements in their remnant state. Thin (18 nm) square elements with edge dimensions between 1 and 10 $\mu$m form closure domain structures with 90 degree Neel walls between domains. We identify two classes of excitations in these systems. The first corresponds to precession of the magnetization about the local demagnetizing field in each quadrant, while the second excitation is localized in the domain walls. Two modes are also identified in ferromagnetic disks with thicknesses of 60 nm and diameters from 2 $\mu$m down to 500 nm. The equilibrium state of each disk is a vortex with a singularity at the center. As in the squares, the higher frequency mode is due to precession about the internal field, but in this case the lower frequency mode corresponds to gyrotropic motion of the entire vortex. These results demonstrate clearly the existence of well-defined excitations in inhomogeneously magnetized microstructures.Comment: PDF File (Figures at reduced resolution

Nonlinearity effects in the kicked oscillator

The quantum kicked oscillator is known to display a remarkable richness of dynamical behaviour, from ballistic spreading to dynamical localization. Here we investigate the effects of a Gross Pitaevskii nonlinearity on quantum motion, and provide evidence that the qualitative features depend strongly on the parameters of the system.Comment: 4 pages, 5 figure