48 research outputs found
Mesoscopic superconductors under irradiation: Microwave spectroscopy of Andreev states
We show that irradiation of a voltage-biased superconducting quantum point
contact at frequencies of the order of the gap energy can remove the
suppression of subgap dc transport through Andreev levels. Quantum interference
among resonant scattering events involving photon absorption is furthermore
shown to make microwave spectroscopy of the Andreev levels feasible. We also
discuss how the same interference effect can be applied for detecting weak
electromagnetic signals up to the gap frequency, and how it is affected by
dephasing and relaxation.Comment: Submitted to a special volume of "Superlattices and Microstructures"
on Mesoscopic Superconductivit
Secondary emission of nanocrystalline zinc oxide
The Raman and photoluminescence (PL) spectra of nanocrystalline zinc oxide produced by mechanochemical synthesis were measured using a pulsed nitrogen laser (337.1 nm) and xenon lamp (360 nm) as excitation sources in PL measurements and a cw Nd:YAG laser in Raman measurements. PL was observed in the range 400–800 nm. The Raman spectrum of nanocrystalline (90 nm) ZnO was compared to that of coarsegrained ZnO. The Raman bands of nanocrystalline zinc oxide were found to be shifted to lower frequencies and broadened. Laser radiation was shown to cause local heating of zinc oxide up to 1000 K, resulting in photoinduced formation of zinc nanoclusters. Mixtures of zinc oxide and sodium chloride powders are heated to substantially lower temperatures. Under nitrogen laser excitation, the green PL band (535 nm), characteristic of bulk ZnO, is shifted to longer wavelengths by 85 nm. The results are interpreted in terms of light confinement in zinc oxide microclusters consisting of large number of nanocrystallites. The photoinduced processes in question may be a viable approach to producing metal-insulator structures in globular photonic crystals, opals, filled with zinc oxide.<br /
Two-level Hamiltonian of a superconducting quantum point contact
In a superconducting quantum point contact, dynamics of the superconducting
phase is coupled to the transitions between the subgap states. We compute this
coupling and derive the two-level Hamiltonian of the contact.Comment: REVTeX, 5 pages, reference adde
Small-Size Resonant Photoacoustic Cell of Inclined Geometry for Gas Detection
A photoacoustic cell intended for laser detection of trace gases is
represented. The cell is adapted so as to enhance the gas-detection performance
and, simultaneously, to reduce the cell size. The cell design provides an
efficient cancellation of the window background (a parasite response due to
absorption of laser beam in the cell windows) and acoustic isolation from the
environment for an acoustic resonance of the cell. The useful photoacoustic
response from a detected gas, window background and noise are analyzed in
demonstration experiments as functions of the modulation frequency for a
prototype cell with the internal volume ~ 0.5 cm^3. The minimal detectable
absorption for the prototype is estimated to be ~ 1.2 10^{-8} cm^{-1} W
Hz^{-1/2}.Comment: 11 pages, 5 figure
Nonequilibrium Josephson effect in mesoscopic ballistic multiterminal SNS junctions
We present a detailed study of nonequilibrium Josephson currents and
conductance in ballistic multiterminal SNS-devices. Nonequilibrium is created
by means of quasiparticle injection from a normal reservoir connected to the
normal part of the junction. By applying a voltage at the normal reservoir the
Josephson current can be suppressed or the direction of the current can be
reversed. For a junction longer than the thermal length, , the
nonequilibrium current increases linearly with applied voltage, saturating at a
value equal to the equilibrium current of a short junction. The conductance
exhibits a finite bias anomaly around . For symmetric
injection, the conductance oscillates -periodically with the phase
difference between the superconductors, with position of the minimum
( or ) dependent on applied voltage and temperature. For
asymmetric injection, both the nonequilibrium Josephson current and the
conductance becomes -periodic in phase difference. Inclusion of barriers
at the NS-interfaces gives rise to a resonant behavior of the total Josephson
current with respect to junction length with a period . Both
three and four terminal junctions are studied.Comment: 21 pages, 19 figures, submitted to Phys. Rev.
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
Generation of Pseudoscalar Bosons by Stimulated Raman Scattering of Light in Dielectric Media
The conditions of pseudoscalar excitations of liquids and crystals vibration states in spontaneous and stimulated Raman spectra revealing are reported. The selection rules for pseudoscalar modes of molecules and crystals observation have been obtained. The experiments on observation of spontaneous and stimulated Raman scattering on pseudoscalar modes of molecules and crystals have been fulfilled. The excitation of stimulated Raman scattering was with using of solid state laser YAG:Nd3+, generating intense (up to 1 TW/cm2) ultrashort (60 ps) laser pulses with energy 10 mJ and frequency repetition 10 Hz. The relationship between pseudoscalar bosons of dielectric media and axion of vacuum is analyzed