Synthetic magnetism for photon fluids

We develop a theory of artificial gauge fields in photon fluids for the cases of both second-order and third-order optical nonlinearities. This applies to weak excitations in the presence of pump fields carrying orbital angular momentum, and is thus a type of Bogoliubov theory. The resulting artificial gauge fields experienced by the weak excitations are an interesting generalization of previous cases and reflect the PT-symmetry properties of the underlying non-Hermitian Hamiltonian. We illustrate the observable consequences of the resulting synthetic magnetic fields for examples involving both second-order and third-order nonlinearities

Low-Temperature Scaling Regime of Random Ferromagnetic-Antiferromagnetic Spin Chains

Using the Continuous Time Quantum Monte Carlo Loop algorithm, we calculate the temperature dependence of the uniform susceptibility, and the specific heat of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down to very low temperatures. Our data show a consistent scaling behavior in both quantities and support strongly the conjecture drawn from the approximative real-space renormalization group treatment. A statistical analysis scheme is developed which will be useful for the search scaling behavior in numerical and experimental data of random spin chains.Comment: 4 pages and 3 figure

Kaon Condensation in the Bound-State Approach to the Skyrme Model

We explore kaon condensation using the bound-state approach to the Skyrme model on a 3-sphere. The condensation occurs when the energy required to produce a $K^-$ falls below the electron fermi level. This happens at the baryon number density on the order of 3--4 times nuclear density.Comment: LaTeX format, 15 pages. 3 Postscript figures, compressed and uuencode

Spin Waves in Random Spin Chains

We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random antiferromagnetic impurity bonds with modified spin-wave theory. By describing thermal excitations in the language of spin waves, we successfully observe a low-temperature Curie susceptibility due to formation of large spin clusters first predicted by the real-space renormalization-group approach, as well as a crossover to a pure ferromagnetic spin chain behavior at intermediate and high temperatures. We compare our results of the modified spin-wave theory to quantum Monte Carlo simulations.Comment: 3 pages, 3 eps figures, submitted to the 47th Conference on Magnetism and Magnetic Material

Predation on migrating eels (Anguilla anguilla L.) from the Western Mediterranean

Nineteen female silver European eels (Anguilla anguilla L.) were tagged with satellite tags and released in the Gulf of Lion in the Mediterranean during the migration seasons 2013 and 2015. Sixteen tags transmitted data: five in the Atlantic Ocean, and eleven in the Mediterranean. Of those, 50% of migrating eels were consumed by marine mammals in each year, all in the Mediterranean. The diving behaviour recorded by the tags after the eels were consumed indicated that the most likely predators were deep diving toothed whales. Measurements of the acoustic target strength of the tag showed a negligible effect on the detectability by whale biosonar. Overall, the observed predation rate was similar to that reported for eels escaping into the Atlantic. However, unlike eels in the Atlantic, which are most vulnerable to predators in the first week of escapement as they traverse the continental shelf and before they reach the refuge of the deep ocean, eels escaping from the Mediterranean were predated in deep water, months after release, likely as a consequence of their migration within a relatively narrow and deep corridor in the Alboran Sea. This emphasises the challenge of accounting for natural mortality in management plans for the long-term recovery of the European eel

Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets

It is conjectured that the Haldane phase of the S=1 antiferromagnetic Heisenberg chain and the $S=1/2$ ferromagnetic-antiferromagnetic alternating Heisenberg chain is stable against any strength of randomness, because of imposed breakdown of translational symmetry. This conjecture is confirmed by the density matrix renormalization group calculation of the string order parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and main text. Final accepted versio

The Low-Energy Fixed Points of Random Quantum Spin Chains

The one-dimensional isotropic quantum Heisenberg spin systems with random couplings and random spin sizes are investigated using a real-space renormalization group scheme. It is demonstrated that these systems belong to a universality class of disordered spin systems, characterized by weakly coupled large effective spins. In this large-spin phase the uniform magnetic susceptibility diverges as 1/T with a non-universal Curie constant at low temperatures T, while the specific heat vanishes as T^delta |ln T| for T->0. For broad range of initial distributions of couplings and spin sizes the distribution functions approach a single fixed-point form, where delta \approx 0.44. For some singular initial distributions, however, fixed-point distributions have non-universal values of delta, suggesting that there is a line of fixed points.Comment: 19 pages, REVTeX, 13 figure

Thermodynamics of Random Ferromagnetic Antiferromagnetic Spin-1/2 Chains

Using the quantum Monte Carlo Loop algorithm, we calculate the temperature dependence of the uniform susceptibility, the specific heat, the correlation length, the generalized staggered susceptibility and magnetization of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down to very low temperatures. Our data show a consistent scaling behavior in all the quantities and support strongly the conjecture drawn from the approximate real-space renormalization group treatment.A statistical analysis scheme is developed which will be useful for the search of scaling behavior in numerical and experimental data of random spin chains.Comment: 13 pages, 13 figures, RevTe

Low Energy Properties of the Random Spin-1/2 Ferromagnetic-Antiferromagnetic Heisenberg Chain

The low energy properties of the spin-1/2 random Heisenberg chain with ferromagnetic and antiferromagnetic interactions are studied by means of the density matrix renormalization group (DMRG) and real space renormalization group (RSRG) method for finite chains. The results of the two methods are consistent with each other. The deviation of the gap distribution from that of the random singlet phase and the formation of the large-spin state is observed even for relatively small systems. For a small fraction of the ferromagnetic bond, the effect of the crossover to the random singlet phase on the low temperature susceptibility and specific heat is discussed. The crossover concentration of the ferromagnetic bond is estimated from the numerical data.Comment: 11 pages, revtex, figures upon reques

Inhomogeneous magnetism in single crystalline Sr3_3CuIrO6+δ_{6+\delta}: Implications to phase-separation concepts

The single crystalline form of an insulator, Sr$_3$CuIrO$_{6+\delta}$, is shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K) with spin-glass-like magnetic susceptibility behaviour. On the basis of this finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we propose that the idea of "phase- separation" described for manganites [1] is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model [2] on {\it magnetic} phase separation in an insulating environment.Comment: 4 pages, 4 figure