Local edge modes in doped cuprates with checkerboard polaronic heterogeneity

We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree-Fock and a random phase approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two dimensions

The Ecology of the Zooplankton Community of a Small Quarry Pond with Special Reference to the Rotifers

This study examines the effect of ecological factors within a small limestone quarry pond environment on the relevant biota. The author collected plankton samples over a period of six months in order to track the vertical distribution patterns within various species of zooplankton, while gathering quantitative data on seasonal physical/chemical changes of the pond. Specimens were collected using a net towed for a distance of 18-27m at depths of 0m, 0.5m, and 1.5 m. On completion, the net was removed from the water and organisms were concentrated into a 30ml vial. The sample was then poured into a different bottle and combined with 20ml of filtered pond water. Samples were transported immediately to the laboratory where all rotifers were live-counted using an A O Spencer binocular microscope. After completing the live count, the researcher preserved the sample and performed a second count using Congo Red stain at a later date. Crustaceans were immediately preserved and counted at a later date. The researcher observed a positive relationship between water temperature and the abundance of zooplankton, and a negative relationship between dissolved oxygen concentrations and planktonic organisms. Crustaceans did not seem to be affected by low concentrations of dissolved O2. The researcher observed that pond depth affected the composition of the zooplankton populations. The researcher concludes that a combination of abiotic and biotic factors appear to play an important role in influencing and regulating zooplankton populations, lessening competition in the relatively shallow quarry pond

Spin Fluctuations and the Pseudogap in Organic Superconductors

We show that there are strong similarities in the spin lattice relaxation of non-magnetic organic charge transfer salts, and that these similarities can be understood in terms of spin fluctuations. Further, we show that, in all of the kappa-phase organic superconductors for which there is nuclear magnetic resonance data, the energy scale for the spin fluctuations coincides with the energy scale for the pseudogap. This suggests that the pseudogap is caused by short-range spin correlations. In the weakly frustrated metals k-(BEDT-TTF)_2Cu[N(CN)_2]Br, k-(BEDT-TTF)_2Cu(NCS)_2, and k-(BEDT-TTF)_2Cu[N(CN)_2]Cl (under pressure) the pseudogap opens at the same temperature as coherence emerges in the (intralayer) transport. We argue that this is because the spin correlations are cut off by the loss of intralayer coherence at high temperatures. We discuss what might happen to these two energy scales at high pressures, where the electronic correlations are weaker. In these weakly frustrated materials the data is well described by the chemical pressure hypothesis (that anion substitution is equivalent to hydrostatic pressure). However, we find important differences in the metallic state of k-(BEDT-TTF)_2Cu_2(CN)_3, which is highly frustrated and displays a spin liquid insulating phase. We also show that the characteristic temperature scale of the spin fluctuations in (TMTSF)_2ClO_4 is the same as superconducting critical temperature, which may be evidence that spin fluctuations mediate the superconductivity in the Bechgaard salts.Comment: 7 pages, 4 figures; to appear in PR