16,192 research outputs found
d-wave Superconductivity in the Hubbard Model
The superconducting instabilities of the doped repulsive 2D Hubbard model are
studied in the intermediate to strong coupling regime with help of the
Dynamical Cluster Approximation (DCA). To solve the effective cluster problem
we employ an extended Non Crossing Approximation (NCA), which allows for a
transition to the broken symmetry state. At sufficiently low temperatures we
find stable d-wave solutions with off-diagonal long range order. The maximal
occurs for a doping and the doping
dependence of the transition temperatures agrees well with the generic
high- phase diagram.Comment: 5 pages, 5 figure
Phase behaviour of binary mixtures of diamagnetic colloidal platelets in an external magnetic field
Using fundamental measure density functional theory we investigate
paranematic-nematic and nematic-nematic phase coexistence in binary mixtures of
circular platelets with vanishing thicknesses. An external magnetic field
induces uniaxial alignment and acts on the platelets with a strength that is
taken to scale with the platelet area. At particle diameter ratio lambda=1.5
the system displays paranematic-nematic coexistence. For lambda=2, demixing
into two nematic states with different compositions also occurs, between an
upper critical point and a paranematic-nematic-nematic triple point. Increasing
the field strength leads to shrinking of the coexistence regions. At high
enough field strength a closed loop of immiscibility is induced and phase
coexistence vanishes at a double critical point above which the system is
homogeneously nematic. For lambda=2.5, besides paranematic-nematic coexistence,
there is nematic-nematic coexistence which persists and hence does not end in a
critical point. The partial orientational order parameters along the binodals
vary strongly with composition and connect smoothly for each species when
closed loops of immiscibility are present in the corresponding phase diagram.Comment: 9 pages, to appear in J.Phys:Condensed Matte
Unified algebraic treatment of resonance
Energy resonance in scattering is usually investigated either directly in the
complex energy plane (E-plane) or indirectly in the complex angular momentum
plane (L-plane). Another formulation complementing these two approaches was
introduced recently. It is an indirect algebraic method that studies resonances
in a complex charge plane (Z-plane). This latter approach will be generalized
to provide a unified algebraic treatment of resonances in the complex E-, L-,
and Z-planes. The complex scaling (rotation) method will be used in the
development of this approach. The resolvent operators (Green's functions) are
formally defined in these three spaces. Bound states spectrum and resonance
energies in the E-plane are mapped onto a discrete set of poles of the
respective resolvent operator on the real line of the L- and Z-planes. These
poles move along trajectories as the energy is varied. A finite square
integrable basis is used in the numerical implementation of this approach.
Stability of poles and trajectories against variation in all computational
parameters is demonstrated. Resonance energies for a given potential are
calculated and compared with those obtained by other studies.Comment: 15 pages, 1 Table, 7 Figures (6 are snapshots of videos
Lasing at the band edges of plasmonic lattices
We report room temperature lasing in two-dimensional diffractive lattices of
silver and gold plasmon particle arrays embedded in a dye-doped polymer that
acts both as waveguide and gain medium. As compared to conventional dielectric
distributed feedback lasers, a central question is how the underlying band
structure from which lasing emerges is modified by both the much stronger
scattering and the disadvantageous loss of metal. We use spectrally resolved
back-focal plane imaging to measure the wavelength- and angle dependence of
emission below and above threshold, thereby mapping the band structure. We find
that for silver particles, the band structure is strongly modified compared to
dielectric reference DFB lasers, since the strong scattering gives large stop
gaps. In contrast, gold particles scatter weakly and absorb strongly, so that
thresholds are higher, but the band structure is not strongly modified. The
experimental findings are supported by finite element and fourier modal method
calculations of the single particle scattering strength and lattice extinction.Comment: 10 pages, 8 figure
41Ca in tooth enamel. part I: A biological signature of neutron exposure in atomic bomb survivors
The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/Ca isotope ratio was (0.17 ± 0.05) × 10-14 in the control samples and increased to 2 × 10-14 for survivors who were proximally exposed to the bomb. The 41Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).Fil: Wallner, A.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; Alemania. Universidad de Viena; AustriaFil: Ruhm, W.. Helmholtz Center Munich German Research Center For Environmental Health; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Rugel, G.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; AlemaniaFil: Nakamura, N.. Radiation Effects Research Foundation; JapónFil: Arazi, Andres. Universitat Technical Zu Munich; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Faestermann, T.. Universitat Technical Zu Munich; AlemaniaFil: Knie, K.. Universitat Technical Zu Munich; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Maier, H. J.. Ludwig Maximilians Universitat; AlemaniaFil: Korschinek, G.. Universitat Technical Zu Munich; Alemani
Quantum Smoluchowski equation: A systematic study
The strong friction regime at low temperatures is analyzed systematically
starting from the formally exact path integral expression for the reduced
dynamics. This quantum Smoluchowski regime allows for a type of semiclassical
treatment in the inverse friction strength so that higher order quantum
corrections to the original quantum Smoluchowski equation [PRL 87, 086802
(2001), PRL 101, 11903 (2008)] can be derived. Drift and diffusion coefficients
are determined by the equilibrium distribution in position and are directly
related to the corresponding action of extremal paths and fluctuations around
them. It is shown that the inclusion of higher order corrections reproduces the
quantum enhancement above crossover for the decay rate out of a metastable well
exactly.Comment: 15 pages, 4 figure
Gauss sum factorization with cold atoms
We report the first implementation of a Gauss sum factorization algorithm by
an internal state Ramsey interferometer using cold atoms. A sequence of
appropriately designed light pulses interacts with an ensemble of cold rubidium
atoms. The final population in the involved atomic levels determines a Gauss
sum. With this technique we factor the number N=263193.Comment: 4 pages, 5 figure
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