Phase-sensitive quantum effects in Andreev conductance of the SNS system of metals with macroscopic phase breaking length

The dissipative component of electron transport through the doubly connected SNS Andreev interferometer indium (S)-aluminium (N)-indium (S) has been studied. Within helium temperature range, the conductance of the individual sections of the interferometer exhibits phase-sensitive oscillations of quantum-interference nature. In the non-domain (normal) state of indium narrowing adjacent to NS interface, the nonresonance oscillations have been observed, with the period inversely proportional to the area of the interferometer orifice. In the domain intermediate state of the narrowing, the magneto-temperature resistive oscillations appeared, with the period determined by the coherence length in the magnetic field equal to the critical one. The oscillating component of resonance form has been observed in the conductance of the macroscopic N-aluminium part of the system. The phase of the oscillations appears to be shifted by $\pi$ compared to that of nonresonance oscillations. We offer an explanation in terms of the contribution into Josephson current from the coherent quasiparticles with energies of order of the Thouless energy. The behavior of dissipative transport with temperature has been studied in a clean normal metal in the vicinity of a single point NS contact.Comment: 9 pages, 7 figures, to be published in Low Temp. Phys., v. 29, No. 12, 200

Development and performance of IR detectors in the 1.5 to 2.4 micrometer region that operate at 240 K

High performance 1.5 to 2.4 micrometers (Hg,Cd)Te photodetectors for operating at 240 K or above are discussed. The detailed characterization of the detector with respect to detector temperature and background flux led to a development of an empirical model for minority carrier trapping. The concept of detective time constant is presented and successfully demonstrated by the four detectors delivered on this contract. An alternative approach is presented with the use of photovoltaic (Hg,Cd)Te detectors

Spin-dependent conductivity of iron-based superconductors in a magnetic field

We report the results of a study of magnetic field features of electron transport in heterojunctions with NS boundary inside iron-based superconductors, represented by a binary phase of $\alpha$ - FeSe and oxyarsenide pnictide LaO(F)FeAs. We used the ability of self magnetic field of the transport current to partially destroy superconductivity, no matter how low the field may be, in the NS interface area, where, due to the proximity effect, the superconducting order parameter, $\Delta$, disperses from 1 to 0 within the scale of the Ginzburg-Landau coherence length. The following features of transport were found:(i) at $T<T_{c}$, magnetoresistance in systems with different superconductors has different sign;(ii) sign and magnitude of the magnetoresistance depend on the magnitude of current and temperature, and (iii) in all operating modes where the contribution from Andreev reflection is suppressed ($(T + eV) \gtrsim \Delta$),the hysteresis of the magnetoresistance is present. Based on the results of the experiment and analysis it has been concluded that there is along-range magnetic order in th eground normal state of the iron-based superconductors studied, in the presence of itinerant magnetism of conduction electrons which determines the possibility of anisotropic spin-dependent exchange interaction with the local magnetic moments of the ions.Comment: 9 pages, 7 figure

Zero differential resistance in two-dimensional electron systems at large filling factors

We report on a state characterized by a zero differential resistance observed in very high Landau levels of a high-mobility two-dimensional electron system. Emerging from a minimum of Hall field-induced resistance oscillations at low temperatures, this state exists over a continuous range of magnetic fields extending well below the onset of the Shubnikov-de Haas effect. The minimum current required to support this state is largely independent on the magnetic field, while the maximum current increases with the magnetic field tracing the onset of inter-Landau level scattering

Long-Distance Contributions to D^0-D^0bar Mixing Parameters

Long-distance contributions to the $D^0$-$\bar D^0$ mixing parameters $x$ and $y$ are evaluated using latest data on hadronic $D^0$ decays. In particular, we take on two-body $D \to PP$ and $VP$ decays to evaluate the contributions of two-body intermediate states because they account for $\sim 50$ of hadronic $D^0$ decays. Use of the diagrammatic approach has been made to estimate yet-observed decay modes. We find that $y$ is of order a few $\times 10^{-3}$ and $x$ of order $10^{-3}$ from hadronic $PP$ and $VP$ modes. These are in good agreement with the latest direct measurement of $D^0$-$\bar D^0$ mixing parameters using the $D^0 \to K_S \pi^+\pi^-$ and $K_S K^+ K^-$ decays by BaBar. We estimate the contribution to $y$ from the $VV$ modes using the factorization model and comment on the single-particle resonance effects and contributions from other two-body modes involving even-parity states.Comment: 18 pages and 1 figure; footnotes and references added; to appear in Phys. Rev.

Non-linear magnetotransport in microwave-illuminated two-dimensional electron systems

We study magnetoresistivity oscillations in a high-mobility two-dimensional electron system subject to both microwave and dc electric fields. First, we observe that the oscillation amplitude is a periodic function of the inverse magnetic field and is strongly suppressed at microwave frequencies near half-integers of the cyclotron frequency. Second, we obtain a complete set of conditions for the differential resistivity extrema and saddle points. These findings indicate the importance of scattering without microwave absorption and a special role played by microwave-induced scattering events antiparallel to the electric field.Comment: 4 pages, 4 figure

Implications of the X-ray Variability for the Mass of MCG-6-30-15

The bright Seyfert 1 galaxy \mcg shows large variability on a variety of time scales. We study the \aproxlt 3 day time scale variability using a set of simultaneous archival observations that were obtained from \rxte and the {\it Advanced Satellite for Cosmology and Astrophysics} (\asca). The \rxte\ observations span nearly $10^6$ sec and indicate that the X-ray Fourier Power Spectral Density has an rms variability of 16%, is flat from approximately 10^{-6} - 10^{-5} Hz, and then steepens into a power law $\propto f^{-\alpha}$ with \alpha\aproxgt 1. A further steepening to $\alpha \approx 2$ occurs between 10^{-4}-10^{-3} Hz. The shape and rms amplitude are comparable to what has been observed in \ngc and \cyg, albeit with break frequencies that differ by a factor of 10^{-2} and 10^{4}, respectively. If the break frequencies are indicative of the central black hole mass, then this mass may be as low as $10^6 {\rm M}_\odot$. An upper limit of $\sim 2$ ks for the relative lag between the 0.5-2 keV \asca band compared to the 8-15 keV \rxte band was also found. Again by analogy with \ngc and \cyg, this limit is consistent with a relatively low central black hole mass.Comment: 5 pages, 3 figures, LaTeX, uses emulateapj.sty and apjfonts.sty, revised version, accepted for publication in ApJ Letter

On the Antenna Beam Shape Reconstruction Using Planet Transit

The calibration of the in-flight antenna beam shape and possible beamdegradation is one of the most crucial tasks for the upcoming Planck mission. We examine several effects which could significantly influence the in-flight main beam calibration using planet transit: the problems of the variability of the Jupiter's flux, the antenna temperature and passing of the planets through the main beam. We estimate these effects on the antenna beam shape calibration and calculate the limits on the main beam and far sidelobe measurements, using observations of Jupiter and Saturn. We also discuss possible effects of degradation of the mirror surfaces and specify corresponding parameters which can help us to determine these effects.Comment: 10 pages, 8 figure