Calculation of NMR Properties of Solitons in Superfluid 3He-A

Superfluid 3He-A has domain-wall-like structures, which are called solitons. We calculate numerically the structure of a splay soliton. We study the effect of solitons on the nuclear-magnetic-resonance spectrum by calculating the frequency shifts and the amplitudes of the soliton peaks for both longitudinal and transverse oscillations of magnetization. The effect of dissipation caused by normal-superfluid conversion and spin diffusion is calculated. The calculations are in good agreement with experiments, except a problem in the transverse resonance frequency of the splay soliton or in magnetic-field dependence of reduced resonance frequencies.Comment: 15 pages, 10 figures, updated to the published versio

Spin 1/2 Fermions in the Unitary Regime: A Superfluid of a New Type

We have studied, in a fully non-perturbative calculation, a dilute system of spin 1/2 interacting fermions, characterized by an infinite scattering length at finite temperatures. Various thermodynamic properties and the condensate fraction were calculated and we have also determined the critical temperature for the superfluid-normal phase transition in this regime. The thermodynamic behavior appears as a rather surprising and unexpected melange of fermionic and bosonic features. The thermal response of a spin 1/2 fermion at the BCS-BEC crossover should be classified as that of a new type of superfluid.Comment: 4 pages, 1 figure, published versio

"Valuing Beach Closures on the Padre Island National Seashore"

In this paper we estimate the economic loss of hypothetical beach closures on the Padre Island National Seashore on the Gulf Coast of Texas. We use a travel cost random utility maximization (RUM) model with data from a random phone survey of Texas residents completed in 2001. We simulate realistic closures that may occur in event of an oil spill or other disruption. For comparison we valued the loss of beach closures in the heavily populated Galveston area. The aggregate losses on Padre Island were highest on weekend days in July estimated at $171,000 per day of closure(2001$). They were lowest on weekdays in September at $25,000. Per trip losses were about$28. A similar closure of beaches near Galveston resulted in losses of $263,000 (week day) and$852,000 (weekend day) with a per trip loss of $30.random utility model, beach use, non-market valuation

Quantitative Probe of Pairing Correlations in a Cold Fermionic Atom Gas

A quantitative measure of the pairing correlations present in a cold gas of fermionic atoms can be obtained by studying the dependence of RF spectra on hyperfine state populations. This proposal follows from a sum rule that relates the total interaction energy of the gas to RF spectrum line positions. We argue that this indicator of pairing correlations provides information comparable to that available from the spin-susceptibility and NMR measurements common in condensed-matter systems.Comment: 5 pages, 1 figur

Superfluidity of Dirac Fermions in a Tunable Honeycomb Lattice: Cooper Pairing, Collective Modes, and Critical Currents

Motivated by recent experiments on atomic Dirac fermions in a tunable honeycomb optical lattice, we study the attractive Hubbard model of superfluidity in the anisotropic honeycomb lattice. At weak-coupling, we find that the maximum mean field pairing transition temperature, as a function of density and interaction strength, occurs for the case with isotropic hopping amplitudes. In this isotropic case, we go beyond mean field theory and study collective fluctuations, treating both pairing and density fluctuations for interaction strengths ranging from weak to strong coupling. We find evidence for a sharp sound mode, together with a well-defined Leggett mode over a wide region of the phase diagram. We also calculate the superfluid order parameter and collective modes in the presence of nonzero superfluid flow. The flow-induced softening of these collective modes leads to dynamical instabilities involving stripe-like density modulations as well as a Leggett-mode instability associated with the natural sublattice symmetry breaking charge-ordered state on the honeycomb lattice. The latter provides a non-trivial test for the experimental realization of the one-band Hubbard model. We delineate regimes of the phase diagram where the critical current is limited by depairing or by such collective instabilities, and discuss experimental implications of our results.Comment: 20 pages, 12 figures. v3: published versio

BCS - BEC crossover at T=0: A Dynamical Mean Field Theory Approach

We study the T=0 crossover from the BCS superconductivity to Bose-Einstein condensation in the attractive Hubbard Model within dynamical mean field theory(DMFT) in order to examine the validity of Hartree-Fock-Bogoliubov (HFB) mean field theory, usually used to describe this crossover, and to explore physics beyond it. Quantum fluctuations are incorporated using iterated perturbation theory as the DMFT impurity solver. We find that these fluctuations lead to large quantitative effects in the intermediate coupling regime leading to a reduction of both the superconducting order parameter and the energy gap relative to the HFB results. A qualitative change is found in the single-electron spectral function, which now shows incoherent spectral weight for energies larger than three times the gap, in addition to the usual Bogoliubov quasiparticle peaks.Comment: 11 pages,12 figures, Published versio