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