Narrow Results

The in-plane resistivity ρ_ab(T) and out-of-plane resistivity ρ_c(T) are measured for Bi₂Sr₂CaCu₂O₈ superconducting thin films successfully deposited by in situ magnetron RF-sputtering on vicinal (100) SrTiO₃ substrates. Oriented film with c axis inclined with respect to the basal plane by a tilt angle α ≈ 4° was obtained. It was found that for the underdoped region ρ_ab(T) deviates from the high T-linear behavior, which evidences the opening of the pseudogap while from the out-of-plane resistivity measurements, we found that the temperature corresponding to the minimum between metallic and semiconducting behavior appears to reflect the opening of the pseudogap for transport along c axis. We also found that the opening of the pseudogap seen in ρ_ab(T) does not coincide with the pseudogap along c axis.

The scaling behavior of the effective activation energy of high-quality epitaxial c-oriented Bi₂Sr₂Ca(Cu_1-xCo_x)₂O_d thin films with 0≤x ≤0.025 has been studied as a function of temperature and magnetic field. For all samples, the effective activation energy scales as U(T, μ_oH)=Uo(1-T/T_c)^mHⁿ with exponent m=1.25±0.03, n=-1/2 and the field scaling 1/μ_oH and -Uμ_oH for thick films and ultra thin films, respectively. The results are discussed taking into account of the influence of the Co substitution with a model in which U(T, H) arises from plastic deformations of the viscous flux liquid above the vortex-glass transition temperature.

The out-of-plane resistivity ρ_c(T) is measured for Bi₂Sr₂CaCu₂O₈ superconducting thin films successfully deposited by in situ magnetron RF–sputtering on vicinal (100) SrTiO₃ substrates. Oriented film with c-axis inclined with respect to the basal plane by a tilt angle α≈4° was obtained. The oxygen content of the film was changed from maximally overdoped state to strongly underdoped nonsuperconducting states. It was found that the temperature corresponding to the minimum between metallic and semiconductive behavior appears to reflect the opening of the pseudogap for transport along c-axis. We found that the opening of the pseudogap along c-axis does not coincide with pseudogap seen in ab plane.

We study the spin oscillations of a quantum dot (QD) embedded in a superconducting ring. The dot is characterized by the Coulomb interaction and the gate voltage. The pairing potential is considered in the superconducting ring. We found that the amplitude and frequency of the oscillations depend sensitively on the pairing potential of superconducting lead, the coupling strength between the dot and superconducting lead. We also show that the magnetic moment on the dot can be controlled by changing the pairing potential of superconducting lead.

MgB₂ thin films were deposited at low temperature substrates, in situ, on c-plane sapphire substrates, with the aluminium nitride (AlN) buffer layers, using the multiple-target sputtering system. The magnetoresistivities were measured using dc-five probe method in applied magnetic field up to 9 Tesla. The upper critical field anisotropy, H_C2(T) and irreversibility field H_irr(T) versus temperature were determined. The Hall coefficients R_H are slightly temperature dependent and positive in the normal state. The critical temperature of 30–32 K and critical current density of 10⁶-10⁷A/cm² at 4.2 K were obtained. Using extracted data, the coherence length ξ_o, anisotropic coefficient γ and penetration depth λ_L were calculated.

The MgB₂ films have been prepared on the c-cut sapphire substrates by ultrasonic spray pyrolysis (USP) technique using Boric acid and Magnesium acetate tetrahydrate dissolved into distillated water and ethanol as starting materials. The overall concentrations were fixed at 0.1mol/L. During the deposition, 96% Ar - 4% H₂ was used as carrier gas. The reaction temperatures were 850 °C, 900 °C and 950 °C . The deposited MgB₂ films showed strongly (1 0 1) plane orientation. In the sample deposited at 950 °C for 5min, MgB₂ film showed a homogeneous surface, with good grain connectivity. The critical temperature (T_c) was observed to be 31.5 K. The crystal structural and microstructural properties of the MgB₂ films prepared by USP were observed to be strongly dependent on the reacting temperature.

The in-plane resistivity ρ_ab(T) are measured for Bi₂Sr₂CaCu₂O₈ superconducting thin films successfully deposited by in situ magnetron RF-sputtering on vicinal (100) SrTiO₃ substrates. Oriented film with c-axis inclined with respect to the basal plane by a tilt angle α≈4° was obtained. The oxygen content of the film was changed from the maximally overdoped state to strongly underdoped nonsuperconducting states. It was found that for underdoped and overdoped regions ρ_ab(T) deviates from the high T-linear behavior at characteristic temperatures T* and T**.

In this paper, a theoretical scheme is proposed to generate the EPR state of two SQUID qubits and create the multipartite cluster states of many SQUID qubits in cavity via Raman transition. We also show how to transfer quantum information from one SQUID qubit to another directly. In this scheme, the cavity field is only virtually excited and thus the cavity decay is suppressed. The quantum information processing and cluster states generation are realized by using only two lower flux states of the SQUID system and the excited state would not be excited. Therefore, the effect of decoherence caused from the levels of the SQUID system is possibly minimized.

This theoretical study of superconductivity examines repulsive forces that, surprisingly, favor the BCS paired state. The value of T_c and the pairing symmetry (s-, p-, d-wave) are obtained exactly as eigenvalues in a given sector of a Fredholm integral equation of the second kind.

We report on the influence of a circular defect on the vortex configuration in a mesoscopic superconducting sample. Effects associated with the pinning force of the circular defect on the configuration and on the vortex entry fields are studied for a very thin disk. We calculate the magnetization loop, vorticity, free energy and superconducting electrons for the disk in presence of an external magnetic field applied perpendicular to the disk plane. The magnetization curves are hysteretic, with paramagnetic response in part of the downward branch, also, in this part we found a vortex–anti-vortex state.

In this paper, we report on the influence of an internal defect on the vortex entrance in a mesoscopic superconducting sample. Effects associated to the pinning force of the defect on the configuration and on the vortex entry fields are studied for a very thin disk. We calculate the supercurrent, magnetization, vorticity, free energy and Cooper pairs density for a disk in presence of external magnetic field applied perpendicular to the disk plane. Due to vortex–defect attraction (repulsion), the vortices always (never) are found to be sitting on the defect position.

In this paper, we solve the Ginzburg–Landau equations for a circular geometry containing a half-circular pillar. We consider the surface of the sample in a complete normal state (|ψ|_surface = 0), this choice, leading to take the extrapolation de Gennes length equal to zero (b = 0). Our results point out that the critical fields, magnetization and vorticity, depend on the chosen boundary condition.

In this paper, we report on the influence of a square (triangular) trench on the superconducting properties of a perforated mesoscopic sample. Effects associated to the pinning force of the hole versus the pinning by the trench and interplay between the shape of the outer boundary and the shape of the inner defects on the vortex configuration are studied for a thin disk. Using the Ginzburg–Landau theory, we calculate the magnetization, vorticity, free energy, magnetic induction, supercurrent and superconducting order parameter as a function of the applied perpendicular magnetic field. We show that only in a restricted range of the magnetic field the vortex configuration obeys the geometry of the trench. Nevertheless, we clearly demonstrate that in our sample new phenomena are possible due to competing interactions of the geometry of the sample and the added geometry of the nanoengineered trench.

In this paper, a double cantilever beam (DCB) specimen incorporating cohesive crack is developed for superconductors which have potential applications in high temperature superconducting cables in space solar power station. The cohesive interface is introduced along the crack front of the DCB model under electromagnetic force. The load-separation relation (i.e. the crack opening displacement) is used as the fracture mechanics parameter and the corresponding curves during fracture process are obtained and verified by the finite element numerical method. Results show that the presence of tensile electromagnetic force makes crack propagate easily. Superconductors with small cracks have good adaptability to the oscillation of magnetic fields while that with large cracks are easier to fracture during the descent of the magnetic field. In addition, the ductility ratio of the cohesive interface can significantly increase the fracture strength. The length of fracture zone decreases as the crack length increases.

More and more studies indicate that the effects of quantum size and energy level statistics play a crucial role in the thermodynamic properties of ultrasmall metallic grains. This paper aims to investigate how they affect the specific heat of ultrasmall metallic grains in magnetic field. As the particle size decreases, fluctuation effects and the impact of energy level separation are becoming more and more important. The method of static path approximation (SPA) is adopted to handle the fluctuation effect. Random matrix theory (RMT) is adopted due to its successful description of the energy level of metal nanoparticles. The normalized specific heat of several typical temperatures and electron spins were taken in the calculation, and the results were analyzed. It was found that spin and the spin-orbit coupling affect the specific heat very obviously, and the suppressed high spin weakens the contribution of electrons to the heat capacity.

We propose a method for realizing quantum logic gates and cluster states with superconducting quantum-interference devices (SQUIDs) in cavity QED via Raman transition. In this proposal, quantum logic gates and cluster states are realized by using only two lower flux states of the SQUID system and the excited state would not be excited. Therefore, the effect of decoherence caused by the levels of the SQUID system is possibly minimized.

This article discusses the main building blocks of a superconducting (SC) linac, the choice of SC resonators, their frequencies, accelerating gradients and apertures, focusing structures, practical aspects of cryomodule design, and concepts to minimize the heat load into the cryogenic system. It starts with an overview of design concepts for all types of hadron linacs differentiated by duty cycle (pulsed or continuous wave) or by the type of ion species (protons, H^-, and ions) being accelerated. Design concepts are detailed for SC linacs in application to both light ion (proton, deuteron) and heavy ion linacs. The physics design of SC linacs, including transverse and longitudinal lattice designs, matching between different accelerating–focusing lattices, and transition from NC to SC sections, is detailed. Design of high-intensity SC linacs for light ions, methods for the reduction of beam losses, preventing beam halo formation, and the effect of HOMs and errors on beam quality are discussed. Examples are taken from existing designs of continuous wave (CW) heavy ion linacs and high-intensity pulsed or CW proton linacs. Finally, we review ongoing R&D work toward high-power SC linacs for various applications.

Based on their great economic value, many current uses and state of the technology, the future of accelerators in medicine, industry, homeland security and research is assured for a long time to come. We review some of the areas in which R&D could have an important impact in the future and mention a few examples.

Part I of this article provides a status update on the ongoing projects for both high-beta and low-beta applications. Some of these projects are already under production, others are perfecting prototypes and future plans. We first cover the funded projects and continue with the planned projects. The update naturally captures the state-of-the-art for superconducting RF (SRF) performance for applications in progress. Part II goes on to present a vision for future prospects for performance progress in the field, along with some advice about the likely fruitful R&D paths to follow. In general, the R&D paths chosen for discussion will benefit most SRF-based accelerators.

Based on their great economic value, many current uses and state of the technology, the future of accelerators in medicine, industry, homeland security and research is assured for a long time to come. We review some of the areas in which R&D could have an important impact in the future and mention a few examples.