High-temperature superconductivity

About: High-temperature superconductivity is a research topic. Over the lifetime, 7263 publications have been published within this topic receiving 175377 citations. The topic is also known as: high-temperature superconductivity.

Instabilities of High Temperature Superconductors

Abstract: We have observed the transition temperature of both the cubic and tetragonal phases of several high-temperature β-W superconductors. The instability of the cubic lattice appears to be characteristic of high-temperature superconductors.

Modeling the microwave properties of superconductors

Abstract: In this paper a macroscopic phenomenological model for the microwave properties of superconductors is presented. The model is based on the idea that there are two kinds of current carriers, and instead of the first London's equation a new equation is derived. This model can be applied to both low- and high-temperature superconductors. Using this model, an expression for the microwave surface resistance is derived and the surface resistance versus frequency is calculated. The results show that the relation between resistance and frequency is not R/sub 3//spl sim//spl omega//sup 2/ as indicated by both BCS theory and London model, but R/sub s//spl sim//spl omega//sup a/, where a is between 1 and 2 (e.g. a=1.35) for thin film high-T/sub c/ superconductors YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. The temperature dependence of R/sub s/ is simulated using the given model. These relations and the values of the surface resistance agree well with experimental results. A residual resistance may be interpreted from this model. >

Microwave/far infrared cavities and waveguides using high temperature superconductors

Abstract: The structures for confining or guiding high frequency electromagnetic radiation have surfaces facing the radiation constructed of high temperature superconducting materials, that is, materials having critical temperatures greater than approximately 35°K. The use of high temperature superconductors removes the constraint of the relatively low energy gaps of conventional, low temperature superconductors which precluded their use at high frequencies. The high temperature superconductors also provide larger thermal margins and more effective cooling. Devices which will benefit from the structures of the invention include microwave cavities, millimeter-wave/far infrared cavities, gyrotron cavities, mode converters, accelerators and free electron lasers, and waveguides.

High-temperature superconductivity and the characteristics of the electronic energy spectrum

Abstract: The possibility is indicated of applying the theory of superconductors with overlapping energy bands to describe the thermodynamic and electromagnetic properties of the high-temperature compounds La2–x(Ba,Sr)xCuO4 and YBa2Cu3O7–δ. The two-band model was used to obtain high values of Tc, two energy gaps 2Δ1/Tc > 3.5 and 2Δ2/Tc < 3.5, large negative values of d ln Tc/d ln V (V is the volume) in lanthanum ceramics, small values of the jump in the electron heat capacity at T = Tc, negative curvature of the upper critical magnetic field H2c near the transition temperature, etc. Such behavior of the above quantities is observed experimentally. A description is also obtained of the decrease in Tc as the disordering of oxygen increases, and also as copper atoms are replaced by a nonmagnetic impurity (Al, Zn, etc.). The main mechanism responsible for this decrease is the interband scattering of electrons by impurities and by randomly distributed oxygen vacancies. A theory has been developed of multiband superconductors which takes into account the points of high symmetry in momentum space. On the basis of this theory one can explain the existence of a plateau in the dependence of Tc on δ for YBa2Cu3O7–δ, and also in the dependence of Tc on x for La2–x(Ba,Sr)xCuO4, that has been observed in a number of experiments. Moreover this theory also explains the presence of two maxima in the dependence of Tc on pressure for Bi2Sr2CaCu2O8.