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.

High-temperature superconductivity in monolayer Bi 2 Sr 2 CaCu 2 O 8+δ

Abstract: Although copper oxide high-temperature superconductors constitute a complex and diverse material family, they all share a layered lattice structure. This curious fact prompts the question of whether high-temperature superconductivity can exist in an isolated monolayer of copper oxide, and if so, whether the two-dimensional superconductivity and various related phenomena differ from those of their three-dimensional counterparts. The answers may provide insights into the role of dimensionality in high-temperature superconductivity. Here we develop a fabrication process that obtains intrinsic monolayer crystals of the high-temperature superconductor Bi2Sr2CaCu2O8+δ (Bi-2212; here, a monolayer refers to a half unit cell that contains two CuO2 planes). The highest superconducting transition temperature of the monolayer is as high as that of optimally doped bulk. The lack of dimensionality effect on the transition temperature defies expectations from the Mermin–Wagner theorem, in contrast to the much-reduced transition temperature in conventional two-dimensional superconductors such as NbSe2. The properties of monolayer Bi-2212 become extremely tunable; our survey of superconductivity, the pseudogap, charge order and the Mott state at various doping concentrations reveals that the phases are indistinguishable from those in the bulk. Monolayer Bi-2212 therefore displays all the fundamental physics of high-temperature superconductivity. Our results establish monolayer copper oxides as a platform for studying high-temperature superconductivity and other strongly correlated phenomena in two dimensions. Transport and scanning tunnelling microscopy studies of freestanding monolayers of an unconventional layered copper oxide establish that the superconducting properties of copper oxides are not changed in the 2D limit.

Evidence from angle-resolved resonant photoemission for oxygen-2p nature of the Fermi-liquid states in Bi2CaSr2Cu2O8

Abstract: It has been generally accepted that a strong on-site Coulomb repulsion of the Cu 3d electrons dominates the electronic structure of the high-transition-temperature (high-Tc) superconductors. The on-site Coulomb repulsion has been evaluated as 6–7 eV, comparable with the valence-band width1,2. This strong correlation is thought to cause the Cu 3d electrons to be localized as in a Mott insulator, and doped holes may be transferred to oxygen sites, as the charge transfer energy is small compared with the correlation energy. These doped holes yield a substantial density of states at the Fermi level, characteristic of metals. There has been great effort to find and characterize the electronic states at the Fermi level, because these states relate directly to the mechanism of the high-Tc superconductivity by providing Cooper pairs below Tc. Here we report the first direct evidence for the dominant oxygen-2p nature of the Fermi-liquid state in the high-Tc superconductor, obtained using the technique of angle-resolved resonant photoemission.

Effect of bismuth on high-Tc cuprate superconductors: Electronic structure of Bi2Sr

Abstract: The electronic structure of the new Bi-based high-temperature superconductor, with ${T}_{c}$ onsets above 110 K, is shown to be altered considerably from that of the other cuprate superconductors by the presence of Bi. There are Bi-O bands which cross the Fermi level, and the two-dimensional character of the bands is even greater than that of previous cuprates. Like the other cuprates, band critical points occur at the Fermi level.

Spin fluctuations in YBa 2 Cu 3 O 6.6

Abstract: An important feature of the high-transition-temperature (high-Tc) copper oxide superconductors is the magnetism that results from the spins associated with the incomplete outer electronic shells (3d9) of the copper ions. Fluctuations of these spins give rise to magnetic excitations of the material, and might mediate the electron pairing that leads to superconductivity. If the mechanism for high-Tc superconductivity is the same for all copper oxide systems, their spin fluctuations should be universal. But so far, theopposite has seemed to be the case: neutron scattering data reveal clear differences between the spin fluctuations for two major classes of high-Tc materials, La2−xSrxCuO4 (1-3) and YBa2Cu3O7−x (4-6), whose respective building blocks are CuO2 layers and bilayers. Here we report two-dimensional neutron-scattering imaging of YBa2Cu3O6.6, which reveals that the low-frequency magnetic excitations are virtually identical to those of similarly doped La2−xSrxCuO4. Thus, the high-temperature (Tc ≲ 92 K) superconductivity of the former materials may be related to spatially coherent low-frequency spin excitations that were previously thought to be unique to the lower-Tc (<40 K) single-layer La2−xSrxCuO4 family.

Flux pinning and creep in very anistropic high temperature superconductors

Abstract: The effect of thermal fluctuations on collective flux-pinning and creeps is investigated for thin-film superconductors and layered superconductors with weak Josephson coupling between the layers in a field normal to the layers and much less than B c2 . Temperature and field dependences of the critical current j c in a two-dimensional (2D) system are obtained. The activation barriers for 2D flux-creep are shown to grow infinitely as U ( j )∝ j -μ at j ⪡ j c , which is characteristics for the vortex-glass state. At very small currents this behaviour is cut off by the plastic motion of edge-dislocation pairs which are either induced by disorder or thermally created, leading to linear current-voltage behaviour inhibiting the existence of a vortex-glass state in 2D systems. The Josephson coupling in layered superconductors changes the dimensionality of the vortex lattice. It is shown that a sufficiently large field when the lattice constant a o becomes less than the characteristic length of the interlayer coupling a 0 r 3D =( R j a 0 ) 1 2 or B > B 2D =Ф 0 / R 2 J , ( R J =Г 1 2 s is the effective Josephson length, s is the interlayer spacing and Г= m z / m is the mass anisotropy), the fluctuations of the vortex lines become of 2D nature. This means in particular that 3D-lattice melting will take place at T = T m , T m is the dislocation-mediated melting temperature of a 2D vortex-lattice. The mixed state at B > B 2D is studied and the possibility of different regimes of pinning and creep is demonstrated. The crossover from 2D to 3D pinning is found when the pinning length R c exceeds r 3D . The crossover conditions are derived and displayed in a schematic phase diagram.