8,097 research outputs found
Maxwell-Chern-Simons Q-balls
We examine the energetics of -balls in Maxwell-Chern-Simons theory in two
space dimensions. Whereas gauged -balls are unallowed in this dimension in
the absence of a Chern-Simons term due to a divergent electromagnetic energy,
the addition of a Chern-Simons term introduces a gauge field mass and renders
finite the otherwise-divergent electromagnetic energy of the -ball. Similar
to the case of gauged -balls, Maxwell-Chern-Simons -balls have a maximal
charge. The properties of these solitons are studied as a function of the
parameters of the model considered, using a numerical technique known as
relaxation. The results are compared to expectations based on qualitative
arguments.Comment: 6 pages. Talk given at Theory CANADA 2, Perimeter Institut
The mean field infinite range p=3 spin glass: equilibrium landscape and correlation time scales
We investigate numerically the dynamical behavior of the mean field 3-spin
spin glass model: we study equilibrium dynamics, and compute equilibrium time
scales as a function of the system size V. We find that for increasing volumes
the time scales increase like . We also present an
accurate study of the equilibrium static properties of the system.Comment: 6 pages, 9 figure
Thermal conductivity in the vicinity of the quantum critical endpoint in Sr3Ru2O7
Thermal conductivity of Sr3Ru2O7 was measured down to 40 mK and at magnetic
fields through the quantum critical endpoint at H_c = 7.85 T. A peak in the
electrical resistivity as a function of field was mimicked by the thermal
resistivity. In the limit as T -> 0 K we find that the Wiedemann-Franz law is
satisfied to within 5% at all fields, implying that there is no breakdown of
the electron despite the destruction of the Fermi liquid state at quantum
criticality. A significant change in disorder (from (H=0T) = 2.1
cm to 0.5 cm) does not influence our conclusions. At
finite temperatures, the temperature dependence of the Lorenz number is
consistent with ferromagnetic fluctuations causing the non-Fermi liquid
behavior as one would expect at a metamagnetic quantum critical endpoint.Comment: 4 figures, published in PR
Interaction between vortices in models with two order parameters
The interaction energy and force between widely separated strings is analyzed
in a field theory having applications to superconducting cosmic strings, the
SO(5) model of high-temperature superconductivity, and solitons in nonlinear
optics. The field theory has two order parameters, one of which is broken in
the vacuum (giving rise to strings), the other of which is unbroken in the
vacuum but which could nonetheless be broken in the core of the string. If this
does occur, there is an effect on the energetics of widely separated strings.
This effect is important if the length scale of this second order parameter is
longer than that of the other fields in the problem.Comment: 11 pages, 3 figures. Minor changes in the text. Accepted for
publication in Phys. Rev.
Cyclotron Resonance in the Layered Perovskite Superconductor Sr2RuO4
We have measured the cyclotron masses in Sr2RuO4 through the observation of
periodic-orbit-resonances - a magnetic resonance technique closely related to
cyclotron resonance. We obtain values for the alpha, beta and gamma Fermi
surfaces of (4.33+/-0.05)me, (5.81+/-0.03)me and (9.71+/-0.11)me respectively.
The appreciable differences between these results and those obtained from de
Haas- van Alphen measurements are attributable to strong electron-electron
interactions in this system. Our findings appear to be consistent with
predictions for a strongly interacting Fermi liquid; indeed, semi-quantitative
agreement is obtained for the electron pockets beta and gamma.Comment: 4 pages + 3 figure
Morphology of the tropopause layer and lower stratosphere above a tropical cyclone : a case study on cyclone Davina (1999)
During the APE-THESEO mission in the Indian Ocean the Myasishchev Design Bureau stratospheric research aircraft M55 Geophysica performed a flight over and within the inner core region of tropical cyclone Davina. Measurements of total water, water vapour, temperature, aerosol backscattering, ozone and tracers were made and are discussed here in comparison with the averages of those quantities acquired during the campaign time frame. Temperature anomalies in the tropical tropopause layer (TTL), warmer than average in the lower part and colder than average in the upper TTL were observed. Ozone was strongly reduced compared to its average value, and thick cirrus decks were present up to the cold point, sometimes topped by a layer of very dry air. Evidence for meridional transport of trace gases in the stratosphere above the cyclone was observed and perturbed water distribution in the TTL was documented. The paper discuss possible processes of dehydration induced by the cirrus forming above the cyclone, and change in the chemical tracer and water distribution in the lower stratosphere 400–430 K due to meridional transport from the mid-latitudes and link with Davina. Moreover it compares the data prior and after the cyclone passage to discuss its actual impact on the atmospheric chemistry and thermodynamics
Application of SQUIDs to low temperature and high magnetic field measurements—ultra low noise torque magnetometry
Authors thank the Max-Planck Society and Deutsche Forschungsgemeinschaft, project “Fermi-surface topology and emergence of novel electronic states in strongly correlated electron systems,” for their financial support.Torque magnetometry is a key method to measure the magnetic anisotropy and quantum oscillations in metals. In order to resolve quantum oscillations in sub-millimeter sized samples, piezo-electric micro-cantilevers were introduced. In the case of strongly correlated metals with large Fermi surfaces and high cyclotron masses, magnetic torque resolving powers in excess of 104 are required at temperatures well below 1 K and magnetic fields beyond 10 T. Here, we present a new broadband read-out scheme for piezo-electric micro-cantilevers via Wheatstone-type resistance measurements in magnetic fields up to 15 T and temperatures down to 200 mK. By using a two-stage superconducting-quantum interference device as a null detector of a cold Wheatstone bridge, we were able to achieve a magnetic moment resolution of Δm = 4 × 10−15 J/T at maximal field and 700 mK, outperforming conventional magnetometers by at least one order of magnitude in this temperature and magnetic field range. Exemplary de Haas-van Alphen measurement of a newly grown delafossite, PdRhO2, was used to show the superior performance of our setup.PostprintPeer reviewe
Ginzburg-Landau Theory for a p-Wave Sr_2RuO_4 Superconductor: Vortex Core Structure and Extended London Theory
Based on a two dimensional odd-parity superconducting order parameter for
Sr_2RuO_4 with p-wave symmetry, we investigate the single vortex and vortex
lattice structure of the mixed phase near H_{c1}. Ginzburg-Landau calculations
for a single vortex show a fourfold structure with an orientation depending on
the microscopic Fermi surface properties. The corresponding extended London
theory is developed to determine the vortex lattice structure and we find near
H_{c1} a centered rectangular vortex lattice. As the field is increased from
H_{c1} this lattice continuously deforms until a square vortex lattice is
achieved. In the centered rectangular phase the field distribution, as
measurable through \mu-SR experiments, exhibits a characteristic two peak
structure (similar to that predicted in high temperature and borocarbide
superconductors).Comment: 12 pages, 7 figure
Tunneling properties at the interface between superconducting Sr2RuO4 and a Ru micro-inclusion
We have investigated the magnetic field and temperature dependence of the
tunneling spectra of the eutectic system Sr2RuO4-Ru. Electric contacts to
individual Ru lamellae embedded in Sr2RuO4 enable the tunneling spectra at the
interface between ruthenate and a Ru microinclusion to be measured. A zero bias
conductance peak (ZBCP) was observed in the bias voltage dependence of the
differential conductance, suggesting that Andreev bound states are present at
the interface. The ZBCP starts to appear at a temperature well below the
superconducting transition temperature. The onset magnetic field of the ZBCP is
also considerably smaller than the upper critical field when the magnetic field
is parallel to the ab-plane. We propose that the difference between the onset
of the ZBCP and the onset of superconductivity can be understood in terms of
the existence of the single-component state predicted by Sigrist and Monien.Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jpn. vol. 74 no.
- …