Hole-Doped Cuprate High Temperature Superconductors

Hole-doped cuprate high temperature superconductors have ushered in the modern era of high temperature superconductivity (HTS) and have continued to be at center stage in the field. Extensive studies have been made, many compounds discovered, voluminous data compiled, numerous models proposed, many review articles written, and various prototype devices made and tested with better performance than their nonsuperconducting counterparts. The field is indeed vast. We have therefore decided to focus on the major cuprate materials systems that have laid the foundation of HTS science and technology and present several simple scaling laws that show the systematic and universal simplicity amid the complexity of these material systems, while referring readers interested in the HTS physics and devices to the review articles. Developments in the field are mostly presented in chronological order, sometimes with anecdotes, in an attempt to share some of the moments of excitement and despair in the history of HTS with readers, especially the younger ones.Comment: Accepted for publication in Physica C, Special Issue on Superconducting Materials; 27 pages, 2 tables, 30 figure

Review on Superconducting Materials

Short review of the topical comprehension of the superconductor materials classes Cuprate High-Temperature Superconductors, other oxide superconductors, Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride Superconductors, Organic and other Carbon-based Superconductors and Boride and Borocarbide Superconductors, featuring their present theoretical understanding and their aspects with respect to technical applications.Comment: A previous version of this article has been published in \" Applied Superconductivity: Handbook on Devices and Applications \", Wiley-VCH ISBN: 978-3-527-41209-9. The new extended and updated version will be published in \" Encyclopedia of Applied Physics \", Wiley-VC

Higher superconducting transition temperature by breaking the universal pressure relation

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconductive transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+{\delta} (Bi2201) and bilayer Bi2Sr2CaCu2O8+{\delta} (Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tc and doping (p) or pressure (P) at higher pressures. The Tc of under-doped Bi2201 initially increases from 9.6 K at ambient to a peak at ~ 23 K at ~ 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above ~ 40 GPa, Tc rises rapidly without any sign of saturation up to ~ 30 K at ~ 51 GPa. Similarly, the Tc for the slightly overdoped Bi2212 increases after passing a broad valley between 20-36 GPa and reaches ~ 90 K without any sign of saturation at ~ 56 GPa. We have therefore attributed this Tc-resurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3d_(x^2-y^2 ) and the O 2p bands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+{\delta} (Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.Comment: 13 pages, including 5 figure

Developments in the negative-U modelling of the cuprate HTSC systems

The paper deals with the many stands that go into creating the unique and complex nature of the HTSC cuprates above Tc as below. Like its predecessors it treats charge, not spin or lattice, as prime mover, but thus taken in the context of the chemical bonding relevant to these copper oxides. The crucial shell filling, negative-U, double-loading fluctuations possible there require accessing at high valent local environment as prevails within the mixed valent, inhomogeneous two sub-system circumstance of the HTSC materials. Close attention is paid to the recent results from Corson, Demsar, Li, Johnson, Norman, Varma, Gyorffy and colleagues.Comment: 44 pages:200+ references. Submitted to J.Phys.:Condensed Matter, Sept 7 200

High Temperature Superconductivity

The current status of basic research on the high temperature cuprate superconductors and prospects for technological applications of these materials is discussed. Recent developments concerning other novel superconductors are also briefly described.Comment: 30 pages, 13 figure

Novel results in STM, ARPES, HREELS, Nernst, neutron, Raman, and isotope substitution experiments and their relation to bosonic modes and charge inhomogeneity, from perspective of negative-Ueff boson-fermion modelling of HTSC

This paper seeks to synthesize much recent work on the HTSC materials around the latest STM results from Davis and coworkers. The conductance diffuse scattering results in particular are used as point of entry to discuss bosonic modes, both of condensed and uncondensed form. The bosonic mode picture is essential to understanding an ever growing range of observations within the HTSC field. The work is expounded within the context of the negative-U, boson-fermion modelling long advocated by the author. This general approach is presently seeing much theoretical development, into which I have looked to couple many of the experimental advances. While the formal theory is not yet sufficiently detailed to cover adequately all the experimental complexities presented by the real cuprate systems, it is clear that it affords very appreciable support to the line taken. An attempt is made throughout to say why and how it is that these events are tied so very closely to this particular set of materials.Comment: 36 pages pdf with 3 figures and 1 table included, Submitted to J. Phys. Cond. Mat

Quench propagation in High Temperature Superconducting materials integrated in high current leads

High temperature superconductors (HTS) have been integrated in the high current leads for the Large Hadron Collider (LHC), under construction at CERN, in order to reduce the heat leak into the liquid helium bath due to the joule effect. The use of the HTS technology in the lower part of the current leads allowed to significantly reduce the heat charge on the cryogenic system. Hybrid current leads have been designed to fulfill the LHC requirements with respect to thermal load; several tests have been performed to study the lead behavior especially during a quench transient. Quench experiments have been performed at CERN on 13 kA prototypes to determine the adequate design and protection. In all the tests it is possible to know the temperature profile of the HTS only with the help of quench simulations that model the thermo-hydraulic processes during quench. The development of a theoretical model for the simulation allows reducing the number of test to perform and to scale the experimental result to other current lead sizes. In this work a theoretical quench model and a numerical code have been developed to compute the quench process and the thermal analysis in the HTS part of the current leads. The model approximates the heat balance equations with the finite difference method and considers the temperature dependence of material's properties. With this model it is possible to perform a thermal analysis of the HTS assembly in steady working condition as well as to study the resistive transition known as quench. The numerical approach is much more accurate than the analytical one, which involves a more approximated model with more physical approximations. In this work are given: the theoretical description of the model, its numerical implementation, the experimental validation and some simulation results

Mechanism of Cation Exchange Process for Epitaxy of Superconducting HgBa2CaCu2O6 Films and Passive Microwave Devices

The record high superconducting transition temperature (Tc) in Hg-based High temperature superconducting (HTS) cuprates make them very promising for both fundamental physics and practical applications. The high volatile nature of Hg presents a major challenge in epitaxy of high quality Hg-based HTS films. In a novel cation exchange process developed by our group recently, epitaxial HgBa2CaCu2O6+δ (Hg-1212) films can be obtained by diffusing volatile Tl cations out of, and simultaneously diffusing Hg cations into, the lattice of epitaxial Tl2Ba2CaCu2O8 (Tl-2212) or TlBa2CaCu2O7 (Tl-1212) precursor films. Aiming at the remained issues in understanding the mechanism of the cation exchange (CE) process, this thesis work has studied the reversibility of CE. We have found that the CE process is completely reversible between Hg-1212 and Tl-2212, confirming further the thermal perturbation diffusion model. One of the experimental works unveiled that the conversion from Hg-1212 to Tl-2212 involves two steps: conversion from Hg-1212 to Tl-1212 via CE followed by Tl intercalation to form double Tl-O plans in each unit cell. Two improvements have been made in raising the quality of the Hg-1212 films. First, by successfully introducing micro-channels in Tl-1212 precursor with reversible CE, purer HTS Hg-1212 thin films have been obtained. Secondly, by pinning lattice with nonvolatile Re atoms, the surface morphology of Hg-1212 films have been improved. In addition to making the high quality Hg-1212 films, we have fabricated a two-pole X-band Hg-1212 microstrip filter and then investigated its nonlinearity by measuring the third-order intermodulation (IM3) signals since the major limitation for real application still comes from the nonlinearity. By a comparison between different structural materials of Hg-1212, Tl-2212 and YBa2Cu3O7 (YBCO), the third-order intercept (IP3) of the Hg-1212 filter is consistently higher than that in the YBCO and Tl-2212. The surprising similarity in the curves of dc critical current density Jc and the rf JIP3 derived from the IP3 against reduced temperature suggests that the magnetic vortex depinning in HTS materials dominates the microwave nonlinearity at elevated temperatures. These encouraging results have marked Hg-1212 out as a promising alternative material for passive microwave devices at above 77 K operating temperature