Theory of the striped superconductor

We define a distinct phase of matter, a "pair density wave" (PDW), in which the superconducting order parameter $\phi$ varies periodically as a function of position such that when averaged over the center of mass position, all components of $\phi$ vanish identically. Specifically, we study the simplest, unidirectional PDW, the "striped superconductor," which we argue may be at the heart of a number of spectacular experimental anomalies that have been observed in the failed high temperature superconductor, La$_{2-x}$ Ba$_x$CuO$_4$. We present a solvable microscopic model with strong electron-electron interactions which supports a PDW groundstate. We also discuss, at the level of Landau theory, the nature of the coupling between the PDW and other order parameters, and the origins and some consequences of the unusual sensitivity of this state to quenched disorder.Comment: 16 pages, 3 figures, 1 table; Journal ref. adde

Fermi-liquid effects in the Fulde-Ferrell-Larkin-Ovchinnikov state of two-dimensional d-wave superconductors

We study the effects of Fermi-liquid interactions on quasi-two-dimensional d-wave superconductors in a magnetic field. The phase diagram of the superconducting state, including the periodic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in high magnetic fields, is discussed for different strengths of quasiparticle many-body interactions within Landau's theory of Fermi liquids. Decreasing the Fermi-liquid parameter $F_0^a$ causes the magnetic spin susceptibility to increase, which in turn leads to a reduction of the FFLO phase. It is shown that a negative $F_0^a$ results in a first-order phase transition from the normal to the uniform superconducting state in a finite temperature interval. Finally, we discuss the thermodynamic implications of a first-order phase transition for CeCoIn$_5$.Comment: published version; removed direct comparison with experiment for the upper critical field, as required by the referee

A study of the nature of perceptual skills in relation to spelling and an analysis of spelling errors

Thesis (Ed.M.)--Boston Universit

Faint Field Galaxies Around Bright Stars - A New Strategy for Imaging at the Diffraction Limit

This paper presents a new strategy for observing faint galaxies with high order natural guide star systems. We have imaged 5 high galactic latitude fields within the isoplanatic patch of bright stars (8.5 < R < 10.3 mag). The fields provide a rich set of faint field galaxies that are observable with a natural guide star adaptive optics system on a large telescope. Due to the small fields of many AO science cameras, these preliminary images are necessary to identify candidate galaxies. We present the photometry and positions for 78 objects (at least 40 galaxies) near five bright stars, appropriate for diffraction limited studies with the Keck and other AO systems on large ground-based telescopes. The K band seeing conditions in each field were excellent (0.4" - 0.7") allowing us to identify stars and estimate galaxy sizes. We also simulate AO images of field galaxies to determine the feasibility of infrared morphological studies at the diffraction limit. With new high order AO systems coming on line with 8-10 meter class telescopes, we believe these observations are invaluable in beginning to study faint galaxy populations at the diffraction limit.Comment: 15 pages, Latex, 9 figures. Accepted for publication in P.A.S.

Energy Efficient Engine exhaust mixer model technology report addendum; phase 3 test program

The Phase 3 exhaust mixer test program was conducted to explore the trends established during previous Phases 1 and 2. Combinations of mixer design parameters were tested. Phase 3 testing showed that the best performance achievable within tailpipe length and diameter constraints is 2.55 percent better than an optimized separate flow base line. A reduced penetration design achieved about the same overall performance level at a substantially lower level of excess pressure loss but with a small reduction in mixing. To improve reliability of the data, the hot and cold flow thrust coefficient analysis used in Phases 1 and 2 was augmented by calculating percent mixing from traverse data. Relative change in percent mixing between configurations was determined from thrust and flow coefficient increments. The calculation procedure developed was found to be a useful tool in assessing mixer performance. Detailed flow field data were obtained to facilitate calibration of computer codes

Profiles of near-resonant population-imbalanced trapped Fermi gases

We investigate the density profiles of a partially polarized trapped Fermi gas in the BCS-BEC crossover region using mean field theory within the local density approximation. Within this approximation the gas is phase separated into concentric shells. We describe how the structure of these shells depends upon the polarization and the interaction strength. A Comparison with experiments yields insight into the possibility of a polarized superfluid phase.Comment: 4 pages, 5 Figures, Published versio

Finite-momentum Bose-Einstein condensates in shaken 2D square optical lattices

We consider ultracold bosons in a 2D square optical lattice described by the Bose-Hubbard model. In addition, an external time-dependent sinusoidal force is applied to the system, which shakes the lattice along one of the diagonals. The effect of the shaking is to renormalize the nearest-neighbor hopping coefficients, which can be arbitrarily reduced, can vanish, or can even change sign, depending on the shaking parameter. It is therefore necessary to account for higher-order hopping terms, which are renormalized differently by the shaking, and introduce anisotropy into the problem. We show that the competition between these different hopping terms leads to finite-momentum condensates, with a momentum that may be tuned via the strength of the shaking. We calculate the boundaries between the Mott-insulator and the different superfluid phases, and present the time-of-flight images expected to be observed experimentally. Our results open up new possibilities for the realization of bosonic analogs of the FFLO phase describing inhomogeneous superconductivity.Comment: 7 pages, 7 figure

Two-dimensional chiral crystals in the NJL model

We investigate the phase structure of the Nambu--Jona-Lasinio model at zero temperature, allowing for a two-dimensional spatial dependence of the chiral condensate. Applying the mean-field approximation, we consider various periodic structures with rectangular and hexagonal geometries, and minimize the corresponding free energy. We find that these two-dimensional chiral crystals are favored over homogeneous phases in a certain window in the region where the phase transition would take place when the analysis was restricted to homogeneous condensates. It turns out, however, that in this regime they are disfavored against a phase with a one-dimensional modulation of the chiral condensate. On the other hand, we find that square and hexagonal lattices eventually get favored at higher chemical potentials. Although stretching the limits of the model to some extent, this would support predictions from quarkyonic-matter studies.Comment: 12 pages, 6 figures. v2: added figure, small modifications, matches published versio

Search for conformal invariance in compressible two-dimensional turbulence

We present a search for conformal invariance in vorticity isolines of two-dimensional compressible turbulence. The vorticity is measured by tracking the motion of particles that float at the surface of a turbulent tank of water. The three-dimensional turbulence in the tank has a Taylor microscale $Re_\lambda \simeq 160$. The conformal invariance theory being tested here is related to the behavior of equilibrium systems near a critical point. This theory is associated with the work of L\"owner, Schramm and others and is usually referred to as Schramm-L\"owner Evolution (SLE). The system was exposed to several tests of SLE. The results of these tests suggest that zero-vorticity isolines exhibit noticeable departures from this type of conformal invariance