1,987 research outputs found
Cluster Dynamical Mean-Field Methods for d-wave Superconductors: the Role of Geometry
We compare the accuracy of two cluster extensions of Dynamical Mean-Field
Theory in describing d-wave superconductors, using as a reference model a
saddle-point t-J model which can be solved exactly in the thermodynamic limit
and at the same time reasonably describes the properties of high-temperature
superconductors. The two methods are Cellular Dynamical Mean-Field Theory,
which is based on a real-space perspective, and Dynamical Cluster
Approximation, which enforces a momentum-space picture by imposing periodic
boundary conditions on the cluster, as opposed to the open boundary conditions
of the first method. We consider the scaling of the methods for large cluster
size, but we also focus on the behavior for small clusters, such as those
accessible by means of present techniques, with particular emphasis on the
geometrical structure, which is definitely a relevant issue in small clusters.Comment: 11 pages, 10 figure
Early performance of constructed oyster reefs in Great Bay, New Hampshire
Several oyster reefs were constructed in Great Bay, New Hampshire using remotely-set oysters. A single large reef treatment and a cluster of several small reefs treatment were utilized to test hypotheses relevant to oyster restoration design, and to monitor early restoration reef performance. There was no significant difference in oyster size, density, and recruitment between two experimental reef structures, with both reef types having high survival and fast growth rates for the 2-year study. Both experimental reef structures had significantly higher recruitment rates than natural reefs in 2006, a year of relatively high recruitment (p \u3c 0.05), and elevated yet not significantly higher recruitment rates in 2005, a weak recruitment year (p = 0.078). In situ fluorometry data showed that a restored reef can significantly impact chlorophyll-a levels in overlying water within two years of reef construction. Individual oyster clearance rates ranged from 1.87 L/hr--2.41L/hr
Signature of antiferromagnetic long-range order in the optical spectrum of strongly correlated electron systems
We show how the onset of a non-Slater antiferromagnetic ordering in a
correlated material can be detected by optical spectroscopy. Using dynamical
mean-field theory we identify two distinctive features: The antiferromagnetic
ordering is associated with an enhanced spectral weight above the optical gap,
and well separated spin-polaron peaks emerge in the optical spectrum. Both
features are indeed observed in LaSrMnO_4 [G\"ossling et al., Phys. Rev. B 77,
035109 (2008)]Comment: 11 pages, 9 figure
Nodal/Antinodal Dichotomy and the Two Gaps of a Superconducting Doped Mott Insulator
We study the superconducting state of the hole-doped two-dimensional Hubbard
model using Cellular Dynamical Mean Field Theory, with the Lanczos method as
impurity solver. In the under-doped regime, we find a natural decomposition of
the one-particle (photoemission) energy-gap into two components. The gap in the
nodal regions, stemming from the anomalous self-energy, decreases with
decreasing doping. The antinodal gap has an additional contribution from the
normal component of the self-energy, inherited from the normal-state pseudogap,
and it increases as the Mott insulating phase is approached.Comment: Corrected typos, 4.5 pages, 4 figure
Kinks: Fingerprints of strong electronic correlations
The textbook knowledge of solid state physics is that the electronic specific
heat shows a linear temperature dependence with the leading corrections being a
cubic term due to phonons and a cubic-logarithmic term due to the interaction
of electrons with bosons. We have shown that this longstanding conception needs
to be supplemented since the generic behavior of the low-temperature electronic
specific heat includes a kink if the electrons are sufficiently strongly
correlatedComment: 4 pages, 1 figure, ICM 2009 conference proceedings (to appear in
Journal of Physics: Conference Series
Off-equilibrium confined dynamics in a glassy system with level-crossing states
We study analytically the dynamics of a generalized p-spin model, starting
with a thermalized initial condition. The model presents birth and death of
states, hence the dynamics (even starting at equilibrium) may go out of
equilibrium when the temperature is varied. We give a full description of this
constrained out of equilibrium behavior and we clarify the connection to the
thermodynamics by computing (sub-dominant) TAP states, constrained to the
starting equilibrium configuration.Comment: 10 pages, 3 figures; longer version with appendi
Resonating bipolarons
Electrons coupled to local lattice deformations end up in selftrapped
localized molecular states involving their binding into bipolarons when the
coupling is stronger than a certain critical value. Below that value they exist
as essentially itinerant electrons. We propose that the abrupt crossover
between the two regimes can be described by resonant pairing similar to the
Feshbach resonance in binary atomic collision processes. Given the
intrinsically local nature of the exchange of pairs of itinerant electrons and
localized bipolarons, we demonstrate the occurrence of such a resonance on a
finite-size cluster made out of metallic atoms surrounding a polaronic ligand
center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
Inducing and controlling magnetism in the honeycomb lattice through a harmonic trapping potential
We study strongly interacting ultracold spin-1/2 fermions in a honeycomb lattice in the presence of a harmonic trap. Tuning the strength of the harmonic trap we show that it is possible to confine the fermions in artificial structures reminiscent of graphene nanoflakes in solid state. The confinement on small structures induces magnetic effects which are absent in a large graphene sheet. Increasing the strength of the harmonic potential we are able to induce different magnetic states, such as a N\ue9el-like antiferromagnetic or ferromagnetic state, as well as mixtures of these basic states. The realization of different magnetic patterns is associated with the terminations of the artificial structures, in turn controlled by the confining potential
High-temperature optical spectral weight and Fermi liquid renormalization in Bi-based cuprates
The optical conductivity and the spectral weight W(T) of two superconducting
cuprates at optimum doping, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, have been first
measured up to 500 K. Above 300 K, W(T) deviates from the usual T2 behavior in
both compounds, even though the zero-frequency extrapolation of the optical
conductivity remains larger than the Ioffe-Regel limit. The deviation is
surprisingly well described by the T4 term of the Sommerfeld expansion, but its
coefficients are enhanced by strong correlation. This renormalization is due to
strong correlation, as shown by the good agreement with dynamical mean field
calculations.Comment: 5 pages, 3 figures, Physical Review Letters in pres
Graphite Nanoeraser
We present here a method for cleaning intermediate-size (5~50nm)
contamination from highly oriented pyrolytic graphite. Electron beam deposition
causes a continuous increase of carbonaceous material on graphene and graphite
surfaces, which is difficult to remove by conventional techniques. Direct
mechanical wiping using a graphite nanoeraser is observed to drastically reduce
the amount of contamination. After the mechanical removal of contamination, the
graphite surfaces were able to self-retract after shearing, indicating that van
der Waals contact bonding is restored. Since contact bonding provides an
indication of a level of cleanliness normally only attainable in a high-quality
clean-room, we discuss potential applications in preparation of ultraclean
surfaces.Comment: 10 pages, two figure
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