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Pairing of fermions is ubiquitous in nature, underlying many phenomena. Examples include superconductivity, superfluidity of ³He, the anomalous rotation of neutron stars, and the crossover between Bose-Einstein condensation of dimers and the BCS (Bardeen, Cooper and Schrieffer) regime in strongly interacting Fermi gases. When confined to two dimensions, interacting many-body systems show even more subtle effects (1), many of which are not understood at a fundamental level. Most striking is the (as yet unexplained) phenomenon of high-temperature superconductivity in copper oxides, which is intimately related to the two-dimensional geometry of the crystal structure. In particular, it is not understood how the many-body pairing is established at high temperature, and whether it precedes superconductivity. Here we report the observation of a many-body pairing gap above the superfluid transition temperature in a harmonically trapped, two-dimensional atomic Fermi gas in the regime of strong coupling. Our measurements of the spectral function of the gas are performed using momentum-resolved photoemission spectroscopy (2,3), analogous to angle-resolved photoemission spectroscopy in the solid state (4). Our observations mark a significant step in the emulation of layered two-dimensional strongly correlated superconductors using ultracold atomic gases., One essential mechanism to establish collective quantum phases in Fermi systems, such as superconductivity or superfluidity, is fermionic pairing. In the case of weak attractive interactions between spin-up and spin-down [...]

An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high [T.sub.c] cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped [YBa.sub.2][Cu.sub.3][O.sub.6+x], revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in [T.sub.c] in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability. fermi surface | high temperature superconductivity | metal-insulator transition | quantum oscillations | quantum critical point doi/10.1073/pnas.0913711107

The question of how thin cuprate layers can be white stilt retaining high-temperature superconductivity (HTS) has been challenging to address, in part because experimental studies require the synthesis of near-perfect ultrathin HTS layers and ways to profile the superconducting properties such as the critical temperature and the superfluid density across interfaces with atomic resolution. We used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal ([La.sub.1.65][Sr.sub.0.45]Cu[O.sub.4]) and a cuprate insulator ([La.sub.2]Cu[O.sub.4]) in which each layer is just three unit cells thick. We selectively doped layers with isovalent Zn atoms, which suppress superconductivity and act as markers, to show that this interface HTS occurs within a single Cu[O.sub.2] plane. This approach may also be useful in fabricating HTS devices. 10.1126/science.1178863

An intense investigation of possible non-Fermi liquid states of matter has been inspired by two of the most intriguing phenomena discovered in the past quarter century, namely, high-temperature superconductivity and the fractional quantum Hall effect. Despite enormous conceptual strides, these two fields have developed largely along separate paths. Two widely employed theories are the resonating valence bond theory for high-temperature superconductivity and the composite fermion theory for the fractional quantum Hall effect. The goal of this perspective article is to note that they subscribe to a common underlying paradigm: They both connect these exotic quantum liquids to certain ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation yields numerous nontrivial experimental consequences, exposing these theories to rigorous and definitive tests.

The realization of high-transition-temperature (high-[T.sub.c]) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications (1, 2) and the opportunity to study quantum phenomena in reduced [...]

In this paper, the transient performance of a magnetic core fault current limiter (FCL) saturated by high temperature superconducting (HTS) dc bias winding is investigated by using both 3-D field-circuit coupled simulation and magnetic circuit analysis. A high voltage is induced on the dc HTS winding during the fault current state. The induced voltage is computed and a short circuit coil for the reduction of induced voltage is studied. The numerical computations are verified by the experiment results on an FCL prototype. Index Terms--Fault current limiter (FCL), field-circuit coupled simulation, high temperature superconductor (HTS), magnetic circuit analysis, saturated core.

AC losses in bulk high-temperature superconductivity rods are calculated using the finite element method. The effect of anisotropy is introduced to the E-J power law considering field dependent critical current density along the axial and azimuthal direction. Influence of the external field on the ac loss components is investigated. Index Terms--Anisotropic critical current density, finite element method, high-temperature bulk superconductors.

High-temperature superconductivity in cuprates was discovered almost exactly 20 years ago, but a satisfactory theoretical explanation for this phenomenon is still lacking. The isotope effect has played an important role in establishing electron-phonon interaction as the dominant interaction in conventional superconductors. Here we present a unified picture of the oxygen isotope effect in cuprate superconductors based on a phonon-mediated d-wave pairing model within the Bardeen-Cooper-Schrieffer theory. We show that this model accounts for the magnitude of the isotope exponent as functions of the doping level as well as the variation between different cuprate superconductors. The isotope effect on the superconducting transition is also found to resemble the effect of pressure on the transition. These results indicate that the role of phonons should not be overlooked for explaining the superconductivity in cuprates. electron-phonon interaction | high-temperature superconductivity | pressure effect

The characteristics analysis of a high-Tc superconducting power supply considering flux creep effect is described. The results suggest that the normal zone resistance and various inductances due to the time constant bring on the current saturation.

It is difficult to accurately simulate supercurrent in high-temperature superconducting bulk even by adopting the finite-element method. The equivalent electrical conductivity of high-temperature superconducting bulk, which has a strong nonlinearity according to the E--J power law, is introduced for the supercurrent analysis. However, the strong nonlinearity results in bad convergency of the nonlinear equation solvers, i.e., the Newton--Raphson (NR) method. Consequently, the unsuitable and/or undulating supercurrent is observed. Therefore, in this paper, the accuracy of the supercurrent analysis in the high-temperature superconducting bulk is discussed and a new method is proposed for the accurate high-temperature superconducting bulk simulation. Then, the method combined a line search with the NR method is adopted as a nonlinear equation solver, and the improvement of convergency and computation time are investigated. Index Terms--E-J power law, high-temperature superconducting (HTS) bulk, nonlinear equation solver, supercurrent distribution.

The flux dynamics method is used to study the electromagnetic phenomena in High Temperature Superconducting (HTS) bulk. The flux evolution, electromagnetic oscillation, the effect of anisotropy and the role of transverse rotating field are discussed.

The main objective of the study is focusing primarily on the acquisition of the V-I characteristic curve under applied magnetic field conditions through the design and implementation of cryogenic HTS measurements apparatus is discussed. In the conclusion the overall operation and output of the measurement apparatus appeared to meet the design goals and produced a vast amount of characteristics data that is useful for the development of power applications involving HTS tape technology.

A versatile co-evaporation system to fabricate coated conductor tape in a continuous way has been built and successfully implemented is studied. Longer coated conductor samples with thicker YBCO films follow to demonstrate that thermal evaporation is one of the most promising candidates for the production of second-generation HTS wire.

A mass boil-off measurement system is used to examine the ac loss of high-temperature superconductor (HTS) coils at frequencies between 50 MHz and 200 MHz, and in applied ac fields of up to 0.04 T.

A high temperature superconducting (HTS) synchronous motor is described and discussed. A magnet with iron plates serves as a field coil and solid nitrogen (SN[subscript 2]) as a cryogen .

A linear actuator with double-sided primary and high-temperature superconducting (HTS) bulk secondary was designed and constructed. Experimental results and analyses are reported.

The transition of trapped fields is investigated, applying an external AC magnetic field to a disk-shaped YBCO bulk.

Fabrication and testing of 10 KVA high temperature superconductive (HTS) transformers are described. Test results demonstrate reliability and overload capability.

Five kinds of cryocooler-cooled high-temperature superconductive (HTS) coils were fabricated and tested to examine the applicability of HTS wires for use with superconducting magnetic energy storage (SMES) applications.

The senisitivity of R[subscript s]-measurement of high-temperature superconductive (HTS) thin films with reference to three resonating techniques is investigated. Shielded dielectic resonator (SDR) is recommended as a possible standard technique.

Interface-engineered junctions on LAAlO[subscript 3] (LAO) and sapphire substrates have been fabricated, using in situ vacuum annealing edge treatment. Improvements in electrical characteristics because of junction narrowing are reported.

The Levitated Dipole Experiment is discussed in the context of the high temperature superconducting levitation coil.

Research describing the propagation of microwave radiation through thin, high temperature superconducting films is presented. Single crystal and bare substrates were investigated in the 60-600 GHz frequency range.

Synthesis in the calcination reaction was facilitated by a coprecipitate precursor.

Charge transport over symmetrical and asymmetrical grain boundaries were studied in YBCO bicrystals grown by liquid phase epitaxy.

Measurements of the microwave surface resistance of YBCO films simultaneously sputtered on both sides of CeO2 coated sapphire wafers are presented.

A demonstration of the unclear temperature dependencies of chi (T) and lambda (T) at Tc-T << Tc for shielding susceptibilities for high-Tc superconductors.

A new study compares conventional and intermodulation measurements of the non-linear microwave response of high-temperature superconductive thin films.

Progress on the development of HTS-coated stainless steel tapes produced by a new high-rate pulsed-laser-deposition method is reported.

The response of YbaCuO bolometers forming an elementary array and thermal crosstalk between adjacent pixels can be predicted using a theoretical modelling approach.

Research describing the behavior of high temperature superconducting power cables when subjected to a short circuit is presented. Simulated tests are analysed with respect to degradation of the cable and cryogenic coolant response.

Research describing the behavior of high temperature superconducting tapes subjected to overcurrents is presented. The effects of short circuits on cable conductors is examined by successive critical current measurements.

The dielectric resonator technique was used to measure surface resistance of high-Tc superconducting films at microwave frequencies.

A new microwave broadband method for measuring the complex resistivity of high temperature superconducting thin films is proposed.

A probe coupling microstrip line resonator was used in the development of a new surface resistance measurement method of high temperature superconductors.

Longitudinal compressive strain effects on critical current in high temperature superconducting tapes were studied.

Doped precursor powders were prepared so that the fabrication of large grain high temperature superconductors could be undertaken.

Bi(Pb)223 bulks were prepared using magnetic melt processing and oriented crystal growth was observed.

A 50Hz single phase high temperature superconducting transformer has been designed, built and characterized.

Bi-Sr-Ca-Cu-O wires with transposed filaments were studied to determine reduction of transport current losses.

Research is presented describing the study and fabrication of a high temperature superconducting convert for use with the sigma-delta A/D bandwidth.

The microstructure of YBa2Cu3O7 superconductor high temperature thin films during thermal cycling was studied using scanning electron microscopy.