32,615 research outputs found
Systematic analysis of a spin-susceptibility representation of the pairing interaction in the 2D Hubbard model
A dynamic cluster quantum Monte Carlo algorithm is used to study a spin
susceptibility representation of the pairing interaction for the
two-dimensional Hubbard model with an on-site Coulomb interaction equal to the
bandwidth for various doping levels. We find that the pairing interaction is
well approximated by {3/2}\Ub(T)^2\chi(K-K') with an effective temperature
and doping dependent coupling \Ub(T) and the numerically calculated spin
susceptibility . We show that at low temperatures, \Ub may be
accurately determined from a corresponding spin susceptibility based
calculation of the single-particle self-energy. We conclude that the strength
of the d-wave pairing interaction, characterized by the mean-field transition
temperature, can be determined from a knowledge of the dressed spin
susceptibility and the nodal quasiparticle spectral weight. This has important
implications with respect to the questions of whether spin fluctuations are
responsible for pairing in the high-T cuprates.Comment: 5 pages, 5 figure
Plasmonics: Localization and guiding of electromagnetic energy in metal/dielectric structures
We review the basic physics of surface-plasmon excitations occurring at metal/dielectric interfaces with special emphasis on the possibility of using such excitations for the localization of electromagnetic energy in one, two, and three dimensions, in a context of applications in sensing and waveguiding for functional photonic devices. Localized plasmon resonances occurring in metallic nanoparticles are discussed both for single particles and particle ensembles, focusing on the generation of confined light fields enabling enhancement of Raman-scattering and nonlinear processes. We then survey the basic properties of interface plasmons propagating along flat boundaries of thin metallic films, with applications for waveguiding along patterned films, stripes, and nanowires. Interactions between plasmonic structures and optically active media are also discussed
Low-energy moments of non-diagonal quark current correlators at four loops
We compute the leading four physical terms in the low-energy expansions of
heavy-light quark current correlators at four-loop order. As a by-product we
reproduce the corresponding top-induced non-singlet correction to the
electroweak rho parameter.Comment: 13 pages, no figures. Extended discussion and added reference
Renormalization group flow for fermions into antiferromagnetically ordered phases: Method and mean-field models
We present a functional renormalization group flow for many-fermion lattice
models into phases with broken spin-rotational symmetry. The flow is expressed
purely in terms of fermionic vertex functions. The symmetry breaking is seeded
by a small initial anomalous self-energy which grows at the transition scale
and which prevents a runaway-flow at nonzero scales. Focusing on the case of
commensurate antiferromagnetism we discuss how the interaction vertex can be
parametrized efficiently. For reduced models with long-range bare interactions
we show the results of standard mean-field theory are reproduced by the fRG and
how anisotropies in the spin sector change the flows. We then describe a more
efficient decomposition of the interaction vertex that should allow for the
treatment of more general models.Comment: revised version; 12 pages, 9 figure
Universality in antiferromagnetic strange metals
We propose a theory of metals at the spin-density wave quantum critical point
in spatial dimension . We provide a first estimate of the full set of
critical exponents (dynamical exponent , correlation length , spin susceptibility , electronic non-Fermi liquid
, spin-wave Landau damping ), which
determine the universal power-laws in thermodynamics and response functions in
the quantum-critical regime relevant for experiments in heavy-fermion systems
and iron pnictides. We present approximate numerical and analytical solutions
of Polchinski-Wetterich type flow equations with soft frequency regulators for
an effective action of electrons coupled to spin-wave bosons. Performing the
renormalization group in frequency -instead of momentum- space allows to track
changes of the Fermi surface shape and to capture Landau damping during the
flow. The technique is easily generalizable from models retaining only patches
of the Fermi surface to full, compact Fermi surfaces.Comment: 46 pages, 13 figures, typos fixed; as accepted to Physical Review
Microscopic Inhomogeneity and Superconducting Properties of a Two-dimensional Hubbard Model for High- Cuprate
Recent scanning tunneling microscopy measurements on cuprate superconductors
have revealed remarkable spatial inhomogeneities in the single-particle energy
gap. Using cellular dynamical mean-field theory, we study the zero temperature
superconducting properties of a single-band Hubbard model with a spatial
modulation of the electron density. We find that the inhomogeneity in the
electronic structure results in a substantial spatial variation in the
superconducting order parameter and single-particle energy gap, reminiscent of
the experimental results. In particular, we find that the order parameter and
gap amplitudes in the hole-rich regions are significantly enhanced over the
corresponding quantities in a uniform system, if the hole-rich regions are
embedded in regions with smaller hole density.Comment: 6 pages, 4 figures, and 2 table
Enhanced Superconductivity in Superlattices of High- Cuprates
The electronic properties of multilayers of strongly correlated models for
cuprate superconductors are investigated using cluster dynamical mean-field
techniques. We focus on combinations of underdoped and overdoped layers and
find that the superconducting order parameter in the overdoped layers is
enhanced by the proximity effect of the strong pairing scale originating from
the underdoped layers. The enhanced order parameter can even exceed the maximum
value in uniform systems. This behavior is well reproduced in slave-boson
mean-field calculations which also find higher transition temperatures than in
the uniform system.Comment: 4 pages, 4 figure
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