Origin of superconductive glassy state and extrinsic critical currents in high-Tc oxides.
TL;DR: The short coherence length of high-${\mathrm{T}$ oxides is shown to induce considerable weakening of the pair potential at surfaces and interfaces, and it is argued that this effect is responsible for the existence of internal Josephson junctions at twin boundaries.
Abstract: The short coherence length of high-${\mathrm{T}}_{\mathrm{c}}$ oxides is shown to induce considerable weakening of the pair potential at surfaces and interfaces. It is argued that this effect is responsible for the existence of internal Josephson junctions at twin boundaries, which are at the origin of the superconductive glassy state, as well as for gapless tunneling characteristics.
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TL;DR: In this article, the authors provide a theoretical basis for understanding the current phase relation (CPhiR) for the stationary Josephson effect in various types of superconducting junctions.
Abstract: This review provides a theoretical basis for understanding the current-phase relation (CPhiR) for the stationary (dc) Josephson effect in various types of superconducting junctions The authors summarize recent theoretical developments with an emphasis on the fundamental physical mechanisms of the deviations of the CPhiR from the standard sinusoidal form A new experimental tool for measuring the CPhiR is described and its practical applications are discussed The method allows one to measure the electrical currents in Josephson junctions with a small coupling energy as compared to the thermal energy A number of examples illustrate the importance of the CPhiR measurements for both fundamental physics and applications
1,084 citations
TL;DR: Stream chemistry data from 100 unpolluted primary forests in temperate South America is reported, and it is suggested that organic nitrogen losses should be considered in models of forest nutrient cycling, which could help to explain observations of nutrient limitation in temperates forest ecosystems.
Abstract: Conceptual and numerical models of nitrogen cycling in temperate forests assume that nitrogen is lost from these ecosystems predominantly by way of inorganic forms, such as nitrate and ammonium ions. Of these, nitrate is thought to be particularly mobile, being responsible for nitrogen loss to deep soil and stream waters. But human activities-such as fossil fuel combustion, fertilizer production and land-use change-have substantially altered the nitrogen cycle over large regions, making it difficult to separate natural aspects of nitrogen cycling from those induced by human perturbations. Here we report stream chemistry data from 100 unpolluted primary forests in temperate South America. Although the sites exhibit a broad range of environmental factors that influence ecosystem nutrient cycles (such as climate, parent material, time of ecosystem development, topography and biotic diversity), we observed a remarkably consistent pattern of nitrogen loss across all forests. In contrast to findings from forests in polluted regions, streamwater nitrate concentrations are exceedingly low, such that nitrate to ammonium ratios were less than unity, and dissolved organic nitrogen is responsible for the majority of nitrogen losses from these forests. We therefore suggest that organic nitrogen losses should be considered in models of forest nutrient cycling, which could help to explain observations of nutrient limitation in temperate forest ecosystems.
635 citations
TL;DR: In this article, experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation, are reviewed from a purely experimental perspective and discussed in the context of present phenomenological theories.
Abstract: We review experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation. This effect has its origin in motion of flux lines out of their pinning sites due to thermal activation or quantum tunneling. The combination of relatively weak flux pinning and high temperatures leads to rich properties that are unconventional in the context of low temperature superconductivity and that have been the subject to intense studies. The results are assessed from a purely experimental perspective and discussed in the context of present phenomenological theories. [S0034-6861(96)00403-5]
590 citations
Cites background from "Origin of superconductive glassy st..."
...Some authors also applied the glassy model to crystals (Deutscher and Müller, 1987; Tinkham, 1988a), though the origin of granularity in crystals is still an open question....
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...superconductor field, an alternative picture based on a model of disordered Josephson links was proposed (Deutscher and Müller, 1987; Morgenstern et al., 1987; Müller et al., 1987, Aksenov and Sergeenkov, 1988)....
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...Phys., Vol. 68, No. 3, July 1996 superconductor field, an alternative picture based on a model of disordered Josephson links was proposed (Deutscher and Müller, 1987; Morgenstern et al., 1987; Müller et al., 1987, Aksenov and Sergeenkov, 1988)....
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TL;DR: In this article, the spatial interrelationships between STM tunneling spectra in underdoped Bi2Sr2CaCu2O8+x were investigated and it was shown that the electronic structure can be divided into 3nm diameter domains with superconducting characteristics and local energy gap delta 50(2.5) meV.
Abstract: Granular superconductivity occurs when microscopic superconducting grains are separated by non-superconducting regions through which they communicate by Josephson tunneling to establish the macroscopic superconducting state [1]. Although crystals of the cuprate high-Tc superconductors are not granular in a structural sense, theory indicates that at low hole densities the holes can become concentrated at some locations resulting in hole-rich superconducting domains [2-5]. Granular superconductivity due to Josephson tunneling through 'undoped' regions between such domains would represent a new paradigm for the underdoped cuprates. Here we report studies of the spatial interrelationships between STM tunneling spectra in underdoped Bi2Sr2CaCu2O8+x. They reveal an apparent spatial segregation of the electronic structure into ~3nm diameter domains (with superconducting characteristics and local energy gap delta 50(2.5) meV. These observations suggest that underdoped Bi2Sr2CaCu2O8+x is a mixture of two different short-range electronic orders with the long-range characteristics of a granular superconductor.
583 citations
TL;DR: In this article, underdoped Bi2Sr2CaCu2O8+δ superconductors are shown to be a mixture of two different short-range electronic orders with the long-range characteristics of a granular superconductor.
Abstract: Granular superconductivity occurs when microscopic superconducting grains are separated by non-superconducting regions; Josephson tunnelling between the grains establishes the macroscopic superconducting state1. Although crystals of the copper oxide high-transition-temperature (high-Tc) superconductors are not granular in a structural sense, theory suggests that at low levels of hole doping the holes can become concentrated at certain locations resulting in hole-rich superconducting domains2,3,4,5. Granular superconductivity arising from tunnelling between such domains would represent a new view of the underdoped copper oxide superconductors. Here we report scanning tunnelling microscope studies of underdoped Bi2Sr2CaCu2O8+δ that reveal an apparent segregation of the electronic structure into superconducting domains that are ∼3 nm in size (and local energy gap 50 ± 2.5 meV. These observations suggest that underdoped Bi2Sr2CaCu2O8+δ is a mixture of two different short-range electronic orders with the long-range characteristics of a granular superconductor.
581 citations