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Universal self-field critical current for thin-film superconductors.

ABSTRACT: For any practical superconductor the magnitude of the critical current density, Jc, is crucially important. It sets the upper limit for current in the conductor. Usually Jc falls rapidly with increasing external magnetic field, but even in zero external field the current flowing in the conductor generates a self-field that limits Jc. Here we show for thin films of thickness less than the London penetration depth, λ, this limiting Jc adopts a universal value for all superconductors-metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type-I superconductors, it is Hc/λ where Hc is the thermodynamic critical field. But surprisingly for type-II superconductors, we find the self-field Jc is Hc1/λ where Hc1 is the lower critical field. Jc is thus fundamentally determined and this provides a simple means to extract absolute values of λ(T) and, from its temperature dependence, the symmetry and magnitude of the superconducting gap.

SUBMITTER: Talantsev EF

PROVIDER: S-EPMC4532791 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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Universal self-field critical current for thin-film superconductors.

Talantsev E F EF Tallon J L JL

Nature communications 20150804

For any practical superconductor the magnitude of the critical current density, Jc, is crucially important. It sets the upper limit for current in the conductor. Usually Jc falls rapidly with increasing external magnetic field, but even in zero external field the current flowing in the conductor generates a self-field that limits Jc. Here we show for thin films of thickness less than the London penetration depth, λ, this limiting Jc adopts a universal value for all superconductors-metals, oxides ...[more]

PMID: 26240014

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Project description:The key impact and significance of a multilayer polymer-based dielectric system on the remarkable photoresponse properties of zinc phthalocyanine (ZnPc)-based photosensitive organic field-effect transistors (PS-OFETs) have been systematically analyzed at various incident optical powers. A combination of inorganic aluminum oxide (Al2O3) and organic nonpolar poly(methyl methacrylate) (PMMA) is used as the bilayer dielectric configuration, whereas in the trilayer dielectric system, a bilayer polymer dielectric, consisting of PMMA, as the low-k dielectric polymer, on top of poly(vinyl alcohol) (PVA), the high-k polar dielectric, has been fabricated along with Al2O3 as the third layer. Before fabricating the OFETs, a systematic optimization of the nature of growth of the ZnPc molecules, deposited on PMMA-coated glass substrates at different substrate temperatures (T s) was performed and examined by atomic-force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and Raman analysis. At 90 °C, the fabricated PS-OFETs with the Al2O3/PVA/PMMA trilayer dielectric configuration showed the best p-channel behavior, with an enhanced and remarkable photoresponsivity of R ∼ 9689.39 A W-1 compared to that of the Al2O3/PMMA bilayer dielectric system (R ∼ 2679.40 A W-1) due to the polarization of the dipoles inside the polar PVA dielectric, which increases the charge transport through the channel. The charge carrier mobility of the device also improved by one order (μh ∼ 1.3 × 10-2 cm2 V-1 s-1) compared to that of the bilayer dielectric configuration (μh ∼ 3.5 × 10-3 cm2 V-1 s-1). The observed specific detectivity (D*) and NEP values of the bilayer dielectric system were 6.01 × 1013 Jones and 2.655 × 10-17 W Hz-1/2, whereas for the trilayer dielectric system, the observed D* and NEP values were 5.13 × 1014 Jones and 1.043 × 10-17 W Hz-1/2, respectively. Additionally, the operating voltage of each of the fabricated devices was also very low (-10 V) due to the influence of the inorganic high-k Al2O3 dielectric layer. The electrical stability of all of the fabricated devices was also investigated by bias stress analysis under both light and dark conditions in vacuum. To the best of our knowledge, the photoresponsivity (R) reported here with an Al2O3/PVA/PMMA trilayer dielectric configuration is the highest reported value for thin film-based PS-OFETs, at a remarkably low operating voltage of -10 V, on low-cost glass substrates without indium tin oxide or/and Si/SiO2.

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Universal self-field critical current for thin-film superconductors.

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Universal self-field critical current for thin-film superconductors.

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