32 research outputs found
Magnetic field induced control of breather dynamics in a single plaquette of Josephson junctions
We present a theoretical study of inhomogeneous dynamic (resistive) states in
a single plaquette consisting of three Josephson junctions. Resonant
interactions of such a breather state with electromagnetic oscillations
manifest themselves by resonant current steps and voltage jumps in the
current-voltage characteristics. An externally applied magnetic field leads to
a variation of the relative shift between the Josephson current oscillations of
two resistive junctions. By making use of the rotation wave approximation
analysis and direct numerical simulations we show that this effect allows to
effectively control the breather instabilities, e. g. to increase (decrease)
the height of the resonant steps and to suppress the voltage jumps in the
current-voltage characteristics.Comment: 4 pages, 3 figure
Spectroscopic observations of the δ Scorpii binary during its recent periastron passage
The bright star δ Sco has been considered a typical B0-type object for many years. Spectra of the star published prior to 1990 showed no evidence of emission, but only of short-term line profile variations attributed to nonradial pulsations. Speckle interferometric observations show that δ Sco is a binary system with a highlyeccentric orbit and a period of ~10.6 years. Weak emission in the Hα line was detected in its spectrum for the rst time during a periastron passage in 1990. Shortly before the next periastron passage in the summer of 2000, the binary entered a strong Hα emission and enhanced mass-loss phase. We monitored the spectroscopic development of the Be outburst from July 2000 through March 2001. In this paper we present results from our spectroscopy, refine elements of the binary orbit, and discuss possible mechanisms for the mass loss.Fabregat Llueca, Juan, [email protected] ;
Blay Serrano, Pedro Jose, [email protected]
Multi-field continuum theory for medium with microscopic rotations
We derive the multi-field, micropolar-type continuum theory for the
two-dimensional model of crystal having finite-size particles. Continuum
theories are usually valid for waves with wavelength much larger than the size
of primitive cell of crystal. By comparison of the dispersion relations, it is
demonstrated that in contrast to the single-field continuum theory constructed
in our previous paper the multi-field generalization is valid not only for long
but also for short waves. We show that the multi-field model can be used to
describe spatially localized short- and long wavelength distortions. Short-wave
external fields of forces and torques can be also naturally taken into account
by the multi-field continuum theory.Comment: 14 pages, 4 figures, submitted to International Journal of Solids and
Structure
Stability of mode-locked kinks in the ac driven and damped sine-Gordon lattice
Kink dynamics in the underdamped and strongly discrete sine-Gordon lattice
that is driven by the oscillating force is studied. The investigation is
focused mostly on the properties of the mode-locked states in the {\it
overband} case, when the driving frequency lies above the linear band. With the
help of Floquet theory it is demonstrated that the destabilizing of the
mode-locked state happens either through the Hopf bifurcation or through the
tangential bifurcation. It is also observed that in the overband case the
standing mode-locked kink state maintains its stability for the bias amplitudes
that are by the order of magnitude larger than the amplitudes in the
low-frequency case.Comment: To appear in Springer Series on Wave Phenomena, special volume
devoted to the LENCOS'12 conference; 6 figure
The Interspersed Spin Boson Lattice Model
We describe a family of lattice models that support a new class of quantum
magnetism characterized by correlated spin and bosonic ordering [Phys. Rev.
Lett. 112, 180405 (2014)]. We explore the full phase diagram of the model using
Matrix-Product-State methods. Guided by these numerical results, we describe a
modified variational ansatz to improve our analytic description of the
groundstate at low boson frequencies. Additionally, we introduce an
experimental protocol capable of inferring the low-energy excitations of the
system by means of Fano scattering spectroscopy. Finally, we discuss the
implementation and characterization of this model with current circuit-QED
technology.Comment: Submitted to EPJ ST issue on "Novel Quantum Phases and Mesoscopic
Physics in Quantum Gases
Observation of breather-like states in a single Josephson cell
We present experimental observation of broken-symmetry states in a
superconducting loop with three Josephson junctions. These states are generic
for discrete breathers in Josephson ladders. The existence region of the
breather-like states is found to be in good accordance with the theoretical
expectations. We observed three different resonant states in the
current-voltage characteristics of the broken-symmetry state, as predicted by
theory. The experimental dependence of the resonances on the external magnetic
field is studied in detail.Comment: 7 pages, 8 figure
Angle-selective all-dielectric Huygens' metasurfaces
We experimentally and numerically study the angularly resolved transmission properties of dielectric metasurfaces consisting of silicon nanodisks which support electric and magnetic dipolar Mie-type resonances in the near-infrared spectral range. First, we concentrate on Huygens' metasurfaces which are characterised by a spectral overlap of the fundamental electric and magnetic dipole resonances of the silicon nanodisks at normal incidence. Huygens' metasurfaces exhibit a high transmitted intensity over the spectral width of the resonances due to impedance matching, while the transmitted phase shows a variation of 2 as the wavelength is swept across the width of the resonances. We observe that the transmittance of the Huygens' metasurfaces depends on the incidence angle and is sensitive to polarisation for non-normal incidence. As the incidence angle is increased starting from normal incidence, the two dipole resonances are shifted out of the spectral overlap and the resonant features appear as pronounced transmittance minima. Next, we consider a metasurface with an increased nanodisk radius as compared to the Huygens' metasurface, which supports spectrally separate electric and magnetic dipole resonances at normal incidence. We show that for TM polarisation, we can shift the resonances of this metasurface into spectral overlap and regain the high resonant transmittance characteristic of Huygens' metasurfaces at a particular incidence angle. Furthermore, both metasurfaces are demonstrated to reject all TM polarised light incident under angles other than the design overlap angle at their respective operation frequency. Our experimental observations are in good qualitative agreement with numerical calculations