2,505 research outputs found
Stability of dynamic coherent states in intrinsic Josephson-junction stacks near internal cavity resonance
Stacks of intrinsic Josephson junctions in the resistive state can by
efficiently synchronized by the internal cavity mode resonantly excited by the
Josephson oscillations. We study the stability of dynamic coherent states near
the resonance with respect to small perturbations. Three states are considered:
the homogeneous and alternating-kink states in zero magnetic field and the
homogeneous state in the magnetic field near the value corresponding to half
flux quantum per junction. We found two possible instabilities related to the
short-scale and long-scale perturbations. The homogeneous state in modulated
junction is typically unstable with respect to the short-scale alternating
phase deformations unless the Josephson current is completely suppressed in one
half of the stack. The kink state is stable with respect to such deformations
and homogeneous state in the magnetic field is only stable within a certain
range of frequencies and fields. Stability with respect to the long-range
deformations is controlled by resonance excitations of fast modes at finite
wave vectors and typically leads to unstable range of the wave-vectors. This
range shrinks with approaching the resonance and increasing the in-plane
dissipation. As a consequence, in finite-height stacks the stability frequency
range near the resonance increases with decreasing the height.Comment: 15 pages, 8 figures, to appear in Phys. Rev.
Interaction of a Nanomagnet with a Weak Superconducting Link
We study electromagnetic interaction of a nanomagnet with a weak
superconducting link. Equations that govern coupled dynamics of the two systems
are derived and investigated numerically. We show that the presence of a small
magnet in the proximity of a weak link may be detected through Shapiro-like
steps caused by the precession of the magnetic moment. Despite very weak
magnetic field generated by the weak link, a time-dependent bias voltage
applied to the link can initiate a non-linear dynamics of the nanomagnet that
leads to the reversal of its magnetic moment. We also consider quantum problem
in which a nanomagnet interacting with a weak link is treated as a two-state
spin system due to quantum tunneling between spin-up and spin-down states.Comment: 7 pages, 4 figure
Dynamical Coulomb Blockade and the Derivative Discontinuity of Time-Dependent Density Functional Theory
The role of the discontinuity of the exchange-correlation potential of
density functional theory is studied in the context of electron transport and
shown to be intimately related to Coulomb blockade. By following the time
evolution of an interacting nanojunction attached to biased leads, we find
that, instead of evolving to a steady state, the system reaches a dynamical
state characterized by correlation-induced current oscillations. Our results
establish a dynamical picture of Coulomb blockade manifesting itself as a
periodic sequence of charging and discharging of the nanostructure.Comment: to appear in Physical Review Letter
Topological confinement in bilayer graphene
We study a new type of one-dimensional chiral states that can be created in
bilayer graphene (BLG) by electrostatic lateral confinement. These states
appear on the domain walls separating insulating regions experiencing the
opposite gating polarity. While the states are similar to conventional
solitonic zero-modes, their properties are defined by the unusual chiral BLG
quasiparticles, from which they derive. The number of zero-mode branches is
fixed by the topological vacuum charge of the insulating BLG state. We discuss
how these chiral states can manifest experimentally, and emphasize their
relevance for valleytronics.Comment: 4 pages, 3 figure
Danialle Karmanos' Work It Out Evaluation Report: Winter/Spring 2013
The DKWIO program seeks to prevent childhood obesity by promoting a healthy mind, body, and spirit through yoga and nutrition programming. The purpose of DKWIO is to help children become healthier by reducing anxiety and increasing self-esteem through the calming and focused effects of yoga. Each week (10 weeks total) children are introduced to a unique one-hour formula that includes an introduction, nutritional information, yoga and activities, as well as relaxation and meditation exercises. The program is delivered by volunteer yoga instructors at urban elementary schools as part of students' existing physical education programming. By the end of the 10 weeks, the DKWIO program goals are that children will have a better understanding of and appreciation for yoga, healthy eating and physical activity, and that incorporating a practice of yoga will improve students' mental and physical health. This report is an evaluation of the program
Coherent current states in mesoscopic four-terminal Josephson junction
A theory is offered for the ballistic 4-terminal Josephson junction. The
studied system consists of a mesoscopic two-dimensional normal rectangular
layer which is attached in each side to the bulk superconducting banks
(terminals). The relation between the currents through the different terminals,
which is valid for arbitrary temperatures and junction sizes, is obtained. The
nonlocal coupling of the supercurrents leads to a new effect, specific for the
mesoscopic weak link between two superconducting rings; an applied magnetic
flux through one of the rings produces a magnetic flux in the other ring even
in the absence of an external flux through the other one. The phase dependent
distributions of the local density of Andreev states, of the supercurrents and
of the induced order parameter are obtained. The "interference pattern" for the
anomalous average inside the two dimensional region can be regulated by the
applied magnetic fluxes or the transport currents. For some values of the phase
differences between the terminals, the current vortex state and the two
dimensional phase slip center are appeared.Comment: 17 pages in Latex and 6 ps Figures. Will be published in Low
Temp.Phy
Conductivity of Paired Composite Fermions
We develop a phenomenological description of the nu=5/2 quantum Hall state in
which the Halperin-Lee-Read theory of the half-filled Landau level is combined
with a p-wave pairing interaction between composite fermions (CFs). The
electromagnetic response functions for the resulting mean-field superconducting
state of the CFs are calculated and used in an RPA calculation of the q and
omega dependent longitudinal conductivity of the physical electrons, a quantity
which can be measured experimentally
Two-instanton approximation to the Coulomb blockade problem
We develop the two-instanton approximation to the current-voltage
characteristic of a single electron transistor within the
Ambegaokar-Eckern-Sch\"on model. We determine the temperature and gate voltage
dependence of the Coulomb blockade oscillations of the conductance and the
effective charge. We find that a small (in comparison with the charging energy)
bias voltage leads to significant suppression of the Coulomb blockade
oscillations and to appearance of the bias-dependent phase shift
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