Material-specific gap function in the high-temperature superconductors

We present theoretical arguments and experimental support for the idea that high-Tc superconductivity can occur with s-wave, d-wave, or mixed-wave pairing in the context of a magnetic mechanism. The size and shape of the gap is different for different materials. The theoretical arguments are based on the t-J model as derived from the Hubbard model so that it necessarily includes three-site terms. We argue that this should be the basic minimal model for high-Tc systems. We analyze this model starting with the dilute limit which can be solved exactly, passing then to the Cooper problem which is numerically tractable, then ending with a mean field approach. It is found that the relative stability of s-wave and d-wave depends on the size and the shape of the Fermi surface. We identify three striking trends. First, materials with large next-nearest-neighbor hopping (such as YBa(2)Cu(3)O(7-x)) are nearly pure d-wave, whereas nearest-neighbor materials (such as La(2-x)Sr(x)CuO(4)) tend to be more s-wave-like. Second, low hole doping materials tend to be pure d-wave, but high hole doping leads to s-wave. Finally, the optimum hole doping level increases as the next-nearest-neighbor hopping increases. We examine the experimental evidence and find support for this idea that gap function in the high-temperature superconductors is material-specific.Comment: 20 pages; requires revtex.sty v3.0, epsf.sty; includes 6 EPS figures; Postscript version also available at http://lifshitz.physics.wisc.edu/www/koltenbah/papers/gapfunc2.ps . This version contains an extensive amount of new work including theoretical background, an additional mean field treatment with new figures, and a more thorough experimental surve

Toward integrated historical climate research: the example of Atmospheric Circulation Reconstructions over the Earth

Climate change has become a key environmental narrative of the 21st century. However, emphasis on the science of climate change has overshadowed studies focusing on human interpretations of climate history, of adaptation and resilience, and of explorations of the institutions and cultural coping strategies that may have helped people adapt to climate changes in the past. Moreover, although the idea of climate change has been subject to considerable scrutiny by the physical sciences, recent climate scholarship has highlighted the need for a re examination of the cultural and spatial dimensions of climate, with contributions from the humanities and social sciences. Establishing a multidisciplinary dialogue and approach to climate research past, present, and future has arguably never been more important. This article outlines developments in historical climatology research and considers examples of integrated multidisciplinary approaches to climate, climatic variability, and climate change research, conducted across the physical sciences, social sciences, humanities, and the arts. We highlight the international Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative as one example of such an integrated approach. Initially, ACRE began as a response from climate science to the needs of the agricultural sector in Queensland, Australia for a longer, more spatially, and temporally-complete database of the weather. ACRE has now evolved to embrace an international group of researchers working together across disciplines to integrate their efforts into a four-dimensional (4D) dynamical global historical climate-quality reanalysis (reconstruction). WIREs Clim Change 2016, 7:164–174. doi:10.1002/wcc.37