37,644 research outputs found
Frequency-dependent ratchet effect in superconducting films with a tilted washboard pinning potential
The influence of an ac current of arbitrary amplitude and frequency on the
mixed-state dc-voltage-ac-drive ratchet response of a superconducting film with
a dc current-tilted uniaxial cosine pinning potential at finite temperature is
theoretically investigated. The results are obtained in the single-vortex
approximation, i.e., for non-interacting vortices, within the frame of an exact
solution of the appropriate Langevin equation in terms of a matrix continued
fraction. Formulas for the dc voltage ratchet response and absorbed power in ac
response are discussed as functions of ac current amplitude and frequency as
well as dc current induced tilt in a wide range of corresponding dimensionless
parameters. Special attention is paid to the physical interpretation of the
obtained results in adiabatic and high-frequency ratchet responses taking into
account both running and localized states of the (ac+dc)-driven vortex motion
in a washboard pinning potential. Our theoretical results are discussed in
comparison with recent experimental work on the high-frequency ratchet response
in nanostructured superconducting films [B. B. Jin et al., Phys. Rev. B 81
(2010) 174505].Comment: 13 pages, 11 figure
New Candidates for Topological Insulators : Pb-based chalcogenide series
Here, we theoretically predict that the series of Pb-based layered
chalcogenides, PbBiSe and PbSbTe, are possible
new candidates for topological insulators. As increases, the phase
transition from a topological insulator to a band insulator is found to occur
between and 3 for both series. Significantly, among the new topological
insulators, we found a bulk band gap of 0.40eV in PbBiSe which is one
of the largest gap topological insulators, and that PbSbTe is
located in the immediate vicinity of the topological phase boundary, making its
topological phase easily tunable by changing external parameters such as
lattice constants. Due to the three-dimensional Dirac cone at the phase
boundary, massless Dirac fermions also may be easily accessible in
PbSbTe
Refugees, trauma and adversity-activated development
The nature of the refugee phenomenon is examined and the position of mental health professionals is located in relation to it. The various uses of the word 'trauma' are explored and its application to the refugee context is examined. It is proposed that refugees' response to adversity is not limited to being traumatized but includes resilience and Adversity-Activated Development (AAD). Particular emphasis is given to the distinction between resilience and AAD. The usefulness of the 'Trauma Grid' in the therapeutic process with refugees is also discussed. The Trauma Grid avoids global impressions and enables a more comprehensive and systematic way of identifying the individual refugee's functioning in the context of different levels, i.e. individual, family, community and society/culture. Finally, I discuss implications for therapeutic work with refugees
NRG for the bosonic single-impurity Anderson model: Dynamics
The bosonic single-impurity Anderson model (B-SIAM) is studied to understand
the local dynamics of an atomic quantum dot (AQD) coupled to a Bose-Einstein
condensation (BEC) state, which can be implemented to probe the entanglement
and the decoherence of a macroscopic condensate. Our recent approach of the
numerical renormalization group (NRG) calculation for the B-SIAM revealed a
zero-temperature phase diagram, where a Mott phase with local depletion of
normal particles is separated from a BEC phase with enhanced density of the
condensate. As an extension of the previous work, we present the calculations
of the local dynamical quantities of the B-SIAM which reinforce our
understanding of the physics in the Mott and the BEC phases.Comment: 12 pages, 13 figure
Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures
We report observations of tunneling anisotropic magnetoresitance (TAMR) in
vertical tunnel devices with a ferromagnetic multilayer-(Co/Pt) electrode and a
non-magnetic Pt counter-electrode separated by an AlOx barrier. In stacks with
the ferromagnetic electrode terminated by a Co film the TAMR magnitude
saturates at 0.15% beyond which it shows only weak dependence on the magnetic
field strength, bias voltage, and temperature. For ferromagnetic electrodes
terminated by two monolayers of Pt we observe order(s) of magnitude enhancement
of the TAMR and a strong dependence on field, temperature and bias. Discussion
of experiments is based on relativistic ab initio calculations of magnetization
orientation dependent densities of states of Co and Co/Pt model systems.Comment: 4 pages, 5 figures, to be published in Phys. Rev. Let
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