Superconductors

We discuss the close link between intermittent events ('quakes') and extremal noise fluctuations which has been advocated in recent numerical and theoretical work. From the idea that record-breaking noise fluctuations trigger the quakes, an approximate analytical description of non-equilibrium aging as a Poisson process with logarithmic time arguments can be derived. Theoretical predictions for measurable statistical properties of mesoscopic fluctuations are emphasized, and supporting numerical evidence is included from simulations of short-ranged Ising spin-glass models, of the ROM model of vortex dynamics in type II superconductors, and of the Tangled Nature model of biological evolution.

Fermilab is developing and investigating different high-field magnet designs for present and future accelerators. The magnet R&D program was focused on the 10-12 T accelerator magnets based on Nb 3 Sn superconductor and explored both basic magnet technologies for brittle superconductors-wind-and-react and react-and-wind. Magnet design studies in support of LHC upgrades and VLHC are being performed. A series of 1-m long single-bore models of cos-theta Nb 3 Sn dipoles based on wind-andreact technique was fabricated and tested. Three 1-m long flat racetracks and the common coil dipole model, based on a singlelayer coil and wide reacted Nb 3 Sn cable, have also been fabricated and tested. Extensive theoretical studies of magnetic instabilities in Nb3Sn strands, cable and magnet were performed which led to successful 10 T dipole model. This paper presents the details of the Fermilab's high field accelerator magnet program, reports its status and major results, and formulates the program next steps.

Retrieved from its original version.

Well known for its accessibility to graduate students and experimental physicists, this volume emphasizes physical arguments and minimizes theoretical formalism. The second edition of this classic text features revisions by the author that improve its user-friendly qualities, and an introductory survey of latter-day developments in classic superconductivity enhances the volume’s value as a reference for researchers. Starting with a historical overview, the text proceeds with an introduction to the electrodynamics of superconductors and presents expositions of the Bardeen-Cooper-Schrieffer theory and the Ginzburg-Landau theory. Additional subjects include magnetic properties of classic type II superconductors; the Josephson effect (both in terms of basic phenomena and applications and of the phenomena unique to small junctions); fluctuation effects in classic superconductors; the high-temperature superconductors; special topics (such as the Bogoliubov method, magnetic perturbations and gapless superconductivity, and time-dependent Ginzburg-Landau theory); and nonequilibrium superconductivity. 1996 edition.

Nucleation of vortices in a superconductor below the first critical field can be assisted by transverse sound in the GHz frequency range. Vortices will enter and exist the superconductor at the frequency of the sound. We compute the threshold parameters of the sound and show that this effect is within experimental reach.

The correlated metal UCoGe is a weak itinerant ferromagnet with a Curie temperature T C = 3 K and a superconductor with a transition temperature T s = 0.6 K. We review its basic thermal, magnetic  on the macro and microscopic scale  and transport properties, as well as the response to high pressure. The data unambiguously show that superconductivity and ferromagnetism coexist below T s = 0.6 K and are carried by the same 5f electrons. We present evidence that UCoGe is a p-wave superconductor and argue that superconductivity is mediated by critical ferromagnetic spin fluctuations.

We analyze the magnetic and electronic properties of the quantum critical heavy fermion superconductor β-YbAlB4, calculating the Fermi surface and the angular dependence of the extremal orbits relevant to the de Haas-van Alphen measurements. Using a combination of the realistic materials modeling and single-ion crystal field analysis, we are led to propose a layered Kondo lattice model for this system, in which two dimensional boron layers are Kondo coupled via interlayer Yb moments in a Jz = ±5/2 state. This model fits the measured single ion magnetic susceptibility and predicts a substantial change in the electronic anisotropy as the system is pressure-tuned through the quantum critical point.

We report pressure and temperature dependent electrical resistivity measurements in the Ce 2 Rh 1Àx Ir x In 8 alloys. Our results revealed two phases with zero resistance. One of these phases is induced by pressure, occurring for a range of compositions situated near the Rhrich extreme, consistent with the behavior observed for the pure Ce 2 RhIn 8 compound. The second transition occurs for intermediate concentrations ðx$0:520:7Þ, and in sharp contrast with the first transition, is progressively eliminated by the application of pressure. We compare the findings in the Ce 2 Rh 1Àx Ir x In 8 alloys to its related CeRh 1Àx Ir x In 5 , discussing how the occurrence of the superconducting phases may become unfavorable for the bi-layer alloys due to higher dimensionality and stronger disorder. r

Polycrystalline samples of FeSe 1-x Te x (x = 0.00, 0.25, 0.50, 0.75 and 1.00) were synthesized by solid-state reaction to study the effects of substituting Se with Te in the system. The magnetization properties of the resulting compounds were investigated and the crystallographic structures of the samples analyzed through X-ray diffraction. Mössbauer spectroscopy was used to determine the ionic state of the Fe ions and the hyperfine fields. The magnetic susceptibility curves of the samples with x = 0.25, 0.50 and 0.75 show superconducting behavior. The lattice parameters and the cell volume increase monotonically with increasing Te concentration and the Mössbauer spectra reveal the absence of internal magnetic hyperfine fields.

A preparation process for YBalCu,O, (afterhere YBCO) superconducting ceramics is presented, in which partial substitution of the copper oxide component by metallic copper is used. The results of an investigation for improving the critical current in YBCO superconductors are also presented. These results show that the YBCO superconductors can be successfully prepared by using the partial metallic copper substitution process. The sintered superconducting ceramics all contain the same pure single phase. The critical current J , of these samples is linearly dependent on the substituted metallic copper content up to 50 wt%. For samples substituted with about 50 wtoh of the copper content J , is improved by a factor of about 1.5, i.e. J , > 300 A/cm2. The experimental values of J , measured at a temperature of 77 K and zero field show that J , is limited by the intergrain tunneling weak-link effect. The linear dependence of J , on the normal state tunneling resistance is in good agreement with the Ambegaokar-Baratoff theory. The energy gap of YBCO superconductors is estimated based on the Ambegaokar-Baratoff theory to be as high as 24 = 7.84kT.

The phonon densities of states (DOS) of insulating BaBi03 and superconducting Bap 6Kp 4Bi03 and the variation of the phonon spectrum of the superconducting compound upon oxygen-isotope (' 0, ' 0) substitution are determined by inelastic neutron scattering (INS) and molecular-dynamics (MD) simulations. The MD simulations are carried out with an effective interaction potential which includes steric effects, Coulomb interactions, and the charge-dipole interactions due to the electronic polarizability of 0 The MD results are in good agreement with the INS experiments and electron-tunneling measurements. Partial DOS of Ba, K, Bi, and 0 in BaBi03 and Bap 6Kp 4Bi03 are also determined from MD simulations. In the superconducting material, the phonon spectrum softens and is comprised of broad bands around 15, 30, and 60 meV. The partial DOS reveal that phonons above 20 meV are due to oxygen vibrations, whereas phonons below 20 meV are due to Ba, K, and Bi. The reference oxygen-isotope-effect exponent, ao, =-t}ln(cp)/t)lnMo, of Bap 6Kp 4BiO, is determined to be ao"=0. 42+0.05 from the mass (Mo) 16O 180 variation of the first moment of the phonon DOS, (cp) and c(cp). This value is close to the oxygenisotope-effect exponent, ao, determined from the variation of T, (0.41+0.03 by Hinks et al. and 0.35+0.05 by Kondoh et al.), indicating that Bap 6Kp 4BiO, is a weak-to moderate-coupling BCS-like superconductor and that the high T, (-30 K) results from large electron-phonon matrix elements involving high-energy oxygen-related phonons.

We consider the theoretical setting of a superfluid like 3He in a rotating container, which is set between the two layers of a type-II superconductor. We describe the superfluid vortices as a 2-dimensional Ising-like model on a triangular lattice in presence of local magnetic fields. The interaction term of the superfluid vortices with the Abrikosov vortices of the superconductor appears then as a symmetry breaking term in the free energy. Such a term gives a higher probability of quantum tunnelling across the potential barrier for bubbles nucleation, thus favouring quantum cavitation.

We have demonstrated advances in mosaic hybridization that will enable very large format far-infrared detectors. Specifically we have produced electrical detector models via mosaic hybridization yielding superconducting circuit paths by hybridizing separately fabricated sub-units onto a single detector unit. The detector model was made on a 100mm diameter wafer while four model readout quadrant chips were made from a separate 100mm wafer. The individually fabricated parts were hybridized using a flip-chip bonder to assemble the detector-readout stack. Once all of the hybridized readouts were in place, a single, large and thick silicon substrate was placed on the stack and attached with permanent epoxy to provide strength and a Coefficient of Thermal Expansion match to the silicon components underneath. Wirebond pads on the readout chips connect circuits to warm readout electronics; and were used to validate the successful superconducting electrical interconnection of the model mosaic-hybrid detector. This demonstration is directly scalable to 150 mm diameter wafers, enabling pixel areas over ten times the area currently available.

The de Haas-van Alphen effect was observed in the underdoped cuprate YBa2Cu3O6.5 via a torque technique in pulsed magnetic fields up to 59 T. Above a field of approximately 30 T the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, closed, and coherent, Fermi surface in the pseudogap phase of cuprates.

Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare recombination rate of quasiparticles, the Cooper pair-breaking rate and the electron-phonon coupling constant, $\lambda=1.1\pm0.1,$ which is in excellent agreement with theoretical estimates.

This report reviews the analysis used to extract the complex conductivity of a compound from a microwave cavity perturbation measurement. We intend to present a generalized treatment valid for any spheroidally shaped sample of arbitrary conductivity which is placed at either the electric or magnetic field antinode of the cavity. To begin with, we establish the relationship between the measured parameters and the conductivity for a spherical sample. Next, we extend these results to the case of spheroids; and for the first time, we cover all different configurations that one can possibly use to study an arbitrary conducting sample inside a cavity: in particular, all possible orientations of the sample with respect to the applied field are solved.

The synthesis of fullerenes was carried out using dc arc discharge technique. The separation and identification of higher fullerene C 84 was done by high performance liquid chromatography (HPLC). The raw soot collected from the high temperature region was dissolved in toluene and then toluene-extracted soot dissolved in n-hexane and kept in laboratory environment for more than one month. The peaks of C 60 and C 70 along with C 84 were observed. The existence of C 84 was confirmed by using linear regression between capacity factor log [k′] and the carbon number.

The oxygenation process of the top seeded melt-grown (TSMG) single-grain YBa2Cu3O7/Y2BaCuO5 (123/211) bulk superconductors was studied by microstructure observations. It is shown that the c-cracks in these bulks are formed in the oxygenated orthorhombic layer along the a/b-macrocracks. The lattice contraction of the 123 phase in a/b-plane induces tensile stresses in the oxygenated layer, which cannot be relaxed by twin boundary motion. The critical spacing of the c-macrocracks, λcr=14 μm, at oxygenation temperature 380 °C, estimated using Thoules’s model, is in a good agreement with the c-macrocrack spacing measures on standard TSMG 123/211 single-grain samples.

For the Cooper/BCS model interaction in superconductors (SCs) it is shown: a) how BCS-Bose crossover picture transition temperatures Tc, defined self-consistently by both the gap and fermion-number equations, require unphysically large couplings to differ significantly from the Tc of ordinary BCS theory defined without the number equation since here the chemical potential is assumed equal to the Fermi energy; how although ignoring either hole- or electron-Cooper-pairs in the recent "complete boson-fermion model": b) one obtains the precise BCS gap equation for all temperatures T, but c) only half the zero-temperature BCS condensation energy emerges. Results (b) and (c) are also expected to hold for neutral-fermion superfluids (SFs)--such as liquid $^3$He, neutron matter and trapped ultra-cold fermion atomic gases--where the pair-forming two-fermion interaction of course differs from the Cooper/BCS one for SCs.

Hysteresis effects in superconducting MgB 2 have been studied systematically by Magnetovoltage Measurements ( curves) as a function of transport current ( ), temperature ( ) and sweep rate of external magnetic field ( ), (d d ). It was observed that time dependent effects appear as the field sweep rate (d d ) varies. This reflects itself as a decrease in the width of loops with decreasing of d d .

The Caldeira-Leggett Hamiltonian describes the interaction of a discrete harmonic oscillator with a continuous bath of harmonic oscillators. This system is a standard model of dissipation in macroscopic low temperature physics, and has applications to superconductors, quantum computing, and macroscopic quantum tunneling. The similarities between the Caldeira-Leggett model and the linearized Vlasov-Poisson equation are analyzed, and it is shown that the damping in the Caldeira-Leggett model is analogous to that of Landau damping in plasmas (Landau, 1946 [1]). An invertible linear transformation (Morrison and Pfirsch, 1992 [18]; Morrison, 2000 [19]) is presented that converts solutions of the Caldeira-Leggett model into solutions of the linearized Vlasov-Poisson system.

A programmable voltage standard of fundamental accuracy has been realized with a binary sequence of nonhysteretic junctions. The series arrays of intrinsically shunted superconductor-insulator-normal conductor-insulator-superconductor (SINIS) Josephson junctions have been fabricated using the reliable Nb-Al/AlO x technology. The arrays of 8192 junctions (14 bit) are arranged in a new, improved design allowing a large Shapiro step width of 1 mA to be achieved.

In this work, the structural effects of the Ca substitution in YBa2Cu307_~ (Ca-123) have been studied by X-ray single crystal structure analysis for the first time. The structure refinements of three single crystals show that at low Ca concentrations (< 11%) y3+ ions are substituted, while at higher concentrations Ca 2÷ also replaces Ba 2÷. Remarkably, no difference in the structural changes has been observed that are due to the apparent substitution for Ba 2+ with Ca 2+ in the more heavily doped samples. Changes in atomic parameters and bond lengths are observed upon Ca doping which are similar in Ca-124 and Ca-247 single crystals. In contrast to ceramic samples, our Ca-123 single crystals are not superconducting probably due to AI doping from the crucible. However, considering doped superconductors, the discussion of structural changes with doping is quite interesting as this work is the first structure refinement of Ca-123 single crystals.

The common features in the Raman data of high temperature superconductors: (the cuprates, bismathates, alkali doped fullerides and some organic superconductors), are analyzed. It was shown that qualitative understanding of the data can be achieved in terms of non-Fermi liquid models for their normal state, with appropiate bag mechanisms for the superconducting state.

We present here combined resistivity and micro-Raman spectroscopy measurements for the superconductor EuBa 2 Cu 3 O 6 + x (Eu-123, EuBCO). We found an important dependence of microstructure and critical temperature on preparation temperature. We also show a strong orientation effect and a T c of 93 K in samples prepared at high temperature relative to those prepared at lower temperature, which exhibit lower T c , broad transitions, and no grain orientation. In addition, we show the influence of annealing conditions on superconducting properties by preparing samples with the same oxygen content (x 0.38) but with various T and P(O 2 ). The peculiar behavior of Eu-123 with temperature by considering a different hole injection sequence for Eu-123 with respect to Y-123 is explained. Micro-Raman measurements seem to support this hypothesis.

The application of flat superconductor rings has been investigated in the structure of inductive shieldtype high temperature superconducting fault current limiters, HT c-SFCL. A laboratory scale inductive shield-type HT c-SFCL has been designed and fabricated using flat superconductor rings. The fabrication process has been fully presented. YBCO powder has been used for the fabrication of superconductor rings. This fabrication process, being quite innovative, is introduced completely. The method of the trapped field measurement has been used for the critical current density measurement of the fabricated superconductor rings. The device with nominal current of 2 A was tested in a 30 V circuit. The SFCL successfully limited the fault currents of up to 10 times the nominal current to an approximately fixed value of 3 A. The voltage-current characteristic of the fabricated prototype has also been obtained and has shown compatibility with the fault current limitation results.

The ground state phase diagram of the 1D Hubbard chain with pair-hopping interaction is studied. The analysis of the model is performed using the continuum-limit field theory approach and exact diagonalization studies. At half-filling the phase diagram is shown to consist of two superconducting states with Cooper pair center-of-mass momentum Q = 0 (BCS-η0 phase) and Q = π (ηπ-phase) and four insulating phases corresponding to the Mott antiferromagnet, the Peierls dimerized phase, the charge-density-wave (CDW) insulator as well as an unconventional insulating phase characterized by the coexistence of a CDW and a bond-located staggered magnetization. Away from half-filling the phase diagram consists of the superconducting BCS-η0 and ηπ phases and the metallic Luttingerliquid phase. The BCS-η0 phase exhibits smooth crossover from a weak-coupling BCS type to a strong coupling local-pair regime. The ηπ phase shows properties of the doublon (zero size Cooper pair) superconductor with Cooper pair center-of-mass momentum Q = π. The transition into the ηπ-paired state corresponds to an abrupt change in the groundstate structure. After the transition the conduction band is completely destroyed and a new ηπ-pair band corresponding to the strongly correlated doublon motion is created.

A deep understanding of the character of superconductivity in the recently discovered Fe-based oxypnictides ReFeAsO 1-x F x (Re = rareearth) necessarily requires the determination of the number of the gaps and their symmetry in k space, which are fundamental ingredients of any model for the pairing mechanism in these new superconductors. In the present paper, we show that point-contact Andreev-reflection experiments performed on LaFeAsO 1-x F x (La-1111) polycrystals with T c ~ 27 K and SmFeAsO 0.8 F 0.2 (Sm-1111) polycrystals with T c ~ 53 K gave differential conductance curves exhibiting two peaks at low bias and two additional structures (peaks or shoulders) at higher bias voltages, an experimental situation quite similar to that observed by the same technique in pure and doped MgB 2 . The single-band Blonder-Tinkham-Klapwijk model is totally unable to properly fit the conductance curves, while the two-gap one accounts remarkably well for the shape of the whole experimental dI/dV vs. V curves. These results give direct evidence of two nodeless gaps in the superconducting state of ReFeAsO 1-x F x (Re = La, Sm): a small gap, 1, smaller than the BCS value (2 1 / k B T c ~ 2.2 -3.2) and a much larger gap 2 which gives a ratio 2 2 / k B T c ~ 6.5 -9. In Sm-1111 both gaps close at the same temperature, very similar to the bulk T c , and follow a BCS-like behaviour, while in La-1111 the situation is more complex, the temperature dependence of the gaps showing remarkable deviations from the BCS behaviour at T close to T c . The normal-state conductance reproducibly shows an unusual, but different, shape in La-1111 and Sm-1111 with a depression or a hump at zero bias, respectively. These structures survive in the normal state up to T * ~ 140 K, close to the temperatures at which structural and magnetic transitions occur in the parent, undoped compound.

We evaluate the low-temperature cutoff for quantum interference 1/τ ϕ induced in a d-wave superconductor by the diffusion enhanced quasiparticle interactions in the presence of disorder. We carry out our analysis in the framework of the non-linear σ-model which allows a direct calculation of 1/τ ϕ , as the mass of the transverse modes of the theory. Only the triplet amplitude in the particle-hole channel and the Cooper amplitude with is pairing symmetry contribute to 1/τ ϕ . We discuss the possible relevance of our results to the present disagreement between thermal transport data in cuprates and the localization theory for d-wave quasiparticles.

We foresee applications and interesting possibilities of incorporating the photonic crystals concept into superconducting electronics. In this paper, we present interesting features of the computed lower band structure of a nondissipative superconductor-dielectric superlattice using the two-fluid model and the transcendental equation [Pochi Yeh, Optical Waves in Layered Media, Wiley Series in Purl and Applied Optics (Wiley, New York, 1988)]. The necessary conditions for approximating the complex conductivity by an imaginary conductivity is derived and the feasibility of achieving the conditions are discussed. The superlattice dispersion obtained is similar to that of the phonon-polariton dispersion in ionic crystal. We found a nonlinear temperature-dependent "polariton gap" and a low-frequency (plasma) gap, and suggested the existence of a photon-superelectron hybrid around the polariton gap. The polariton gap may be observed in an infrared-microwave regime using a high-T-c, superconductor with sufficiently low normal-fluid relaxation time (approximate to 10(-15) s), and in an optical regime using lower penetration depth (approximate to 50 nm) and extremely low relaxation time (approximate to 10(-17) s).

We give a review of recent results on the heavy fermion superconductor CeRhIn5 which presents ideal conditions to study the interplay of antiferromagnetism and superconductivity. The main results are the appearance of domains of microscopic coexistence of antiferromagnetism and superconductivity under both, pressure and magnetic field scans. At zero magnetic field, under pressure coexistence appears from the onset of pressure induced superconductivity up to the critical pressure p ⋆ c where antiferrmognetism disappears abruptly. Under magnetic field, re-entrance of magnetic order inside the superconducting state occurs in the pressure range from p ⋆ c up to pc. The antiferromagnetic quantum critical point is hidden by the onset of superconductivity. A striking point is the similarity of the phase diagram of CeRhIn5 and that of the high Tc cuprate superconductors where for the cuprates the carrier concentration replaces the pressure. Both systems are characterized by: hidden magnetic quantum criticality, field reentrance of magnetism and the strong link to a Fermi surface instability.

The frequency response of pinned vortex lattice in type-II superconductors is investigated. If frequency is not too low than the AC-absorption is caused by oscillations of the vortex lattice near equilibrium state (Campbell regime). We calculate the field and temperature dependencies ofboth Campbell penetration depth and surface resistance, taking into account the effect of the thermal depinning. In the region of low frequencies jumps of lattice regions between different metastable states (two-level systems) come into play and give main contribution to the AC-response. The field and temperature dependencies of the penetration depth and surface resistance in the last region are also found.

We report a detailed study of the electronic and structural properties of the 39K superconductor \mgbtwo and of several related systems of the same family, namely \mgalbtwo, \bebtwo, \casitwo and \cabesi. Our calculations, which include zone-center phonon frequencies and transport properties, are performed within the local density approximation to the density functional theory, using the full-potential linearized augmented plane wave

During the Engineering Design Activity (EDA) of the ITER program a major effort is being devoted to conductor R&D for the ITER magnets systems. This program includes all aspects of cable-in-conduit-conductor (CICC) manufacturing development such as superconducting strand, large multistage cables, and fabrication of thick-wall and thin-wall conduits. It also includes an extensive program of small scale laboratory measurements and experiments designed to predict the full-size conductor and magnet performance, and to quantify elements of the conductor design guidelines. A description of the manufacturing development and experimental program is given, including experiments for determining AC losses in the superconductor, CICC stability under DC and fast ramped conditions of field and current, and development of novel quench detection techniques.

We report quantum oscillation measurements in SrFe 2 As 2-which is an antiferromagnetic parent of the iron-arsenide family of superconductors-known to become superconducting under doping and the application of pressure. The magnetic field and temperature dependences of the oscillations between 20 and 55 T in the liquid helium temperature range suggest that the electronic excitations are those of a Fermi liquid. We show that the observed Fermi surface comprising small pockets is consistent with the formation of a spin-density wave. Our measurements thus demonstrate that high T c superconductivity can occur on doping or pressurizing a conventional metallic spin-density wave state.

Now a team led by MIT's Plasma Science and Fusion Center (PSFC) and MIT spinout company Commonwealth Fusion Systems (CFS), has developed and extensively tested an HTS cable technology that can be scaled and engineered into the high-performance magnets. [30] Using a clever technique that causes unruly crystals of iron selenide to snap into alignment, Rice University physicists have drawn a detailed map that reveals the "rules of the road" for electrons both in normal conditions and in the critical moments just before the material transforms into a superconductor. [29] Superconducting quantum microwave circuits can function as qubits, the building blocks of a future quantum computer. [28] Physicists have shown that superconducting circuits-circuits that have zero electrical resistance-can function as piston-like mechanical quantum engines. The new perspective may help researchers design quantum computers and other devices with improved efficiencies. [27] This paper explains the magnetic effect of the superconductive current from the observed effects of the accelerating electrons, causing naturally the experienced changes of the electric field potential along the electric wire. The accelerating electrons explain not only the Maxwell Equations and the Special Relativity, but the Heisenberg Uncertainty Relation, the wave particle duality and the electron's spin also, building the bridge between the Classical and Quantum Theories. The changing acceleration of the electrons explains the created negative electric field of the magnetic induction, the Higgs Field, the changing Relativistic Mass and the Gravitational Force, giving a Unified Theory of the physical forces. Taking into account the Planck Distribution Law of the electromagnetic oscillators also, we can explain the electron/proton mass rate and the Weak and Strong Interactions. Since the superconductivity is basically a quantum mechanical phenomenon and some entangled particles give this opportunity to specific matters, like Cooper Pairs or other entanglements, as strongly correlated materials and Exciton-mediated electron pairing, we can say that the secret of superconductivity is the quantum entanglement.

A new test for measurement of the mechanical properties of granular powders is proposed, consisting of upsetting the powder inside a metal tube. Varying the tube material as well as its wall thickness allows superimposing of a variable radial pressure. By pre-compacting the powder inside the tube in a closed die it is possible to test the powder at different densities. The radial pressure is found by correlating measurements of radial bulging of the tube with numerical analysis of tube bulging. Estimates of the error on the determination of the radial pressure are given and it is found that this error may be kept less than T 4%. The coefficient of friction between powder and tube for a specific case is evaluated and found to be between 0.05 and 0.1 at p c > 400 MPa. Data from the test with axial pressures up to 1100 MPa and radial pressures up to 500 MPa are presented. Data on the yield surface for BSCCO (ceramic powder (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x for manufacturing of superconductors) at 74% density are given and found to be in good agreement with previously published data determined by closed die compaction and fracture tests.

nature materials | VOL 2 | JULY 2003 | www.nature.com/naturematerials 487 A fter early studies of high-temperature superconducting materials such as YBaCuO revealed that high-angle grain boundaries act as severe weak links for current transport 1,2 , substantial research has been directed towards the development of long lengths of crystallographically aligned superconductors 3 . One approach has been to induce alignment using the epitaxial growth of oxide films on rollingassisted biaxially textured substrates (RABiTS) 4 .Rolled Ni substrates are recrystallized under conditions that lead to a high degree of biaxial {001}<100> cube texture. Subsequent growth of epitaxial oxide buffer layers (typically CeO 2 and YSZ as chemical barriers) and superconducting YBCO preserves the alignment, enabling high critical current densities, J c > 10 6 cm -2 . Conventional monochromatic X-ray ωand φ-scans typically reveal macroscopic biaxial texture to withiñ 5°-10°full-width at half-maximum (FWHM) for all layers,but do not describe local microstructural features that control the materials properties.We note that in the case of brittle oxide films on ductile metal substrates, epitaxial growth involves strain interactions between two materials with disparate elastic properties. Understanding and controlling the local texture and microstructural evolution of processes associated with heteroepitaxial growth,differential thermal contraction and cracking remain significant challenges in this complex system 5,6 , as well as in many other technologically important thin-film applications.

The behavior of electromagnetic fields in high-Tc superconductors (HTSs) is studied in order to examine their effects in classical electromagnetic boundary value problems. It is shown that an HTS can not be simply treated as a low loss conductor and boundary conditions of HTSs cannot be considered as perfect conducting boundaries like conventional treatments. The electromagnetics of HTS are investigated in terms of complex conductivity, surface impedance with applied magnetic fields, and computational electrodynamics using the proposed model

NbN superconductor and wide band gap AlN thin films were deposited using sputtering at room temperature. Study of the nitride interfaces are forerunner to the growth Josephson junctions that are considered able to work in the terahertz frequency. We find that to be compatible with lithography technology and to have a high critical transition temperature, the substrate should not be overheated, and this means working in low power regime to limit the induced heating of the plasma. X-ray photoelectron spectroscopy and X-ray diffraction analysis were performed on samples deposited on crystalline, amorphous, flexible, and nanostructured substrates. The experimental results suggest us how to improve the deposition process in order to obtain the best nitride films as well as NbN/AlN/NbN trilayers for Josephson junction applications.

In this study, Ferrite A (undoped barium hexaferrite), Ferrite B (MnCuNi-doped barium hexaferrite), Ferrite C (MnCuSr-doped barium hexaferrite), Ferrite D (MnCoNi-doped barium hexaferrite) and Ferrite E (MnCoSr-doped barium hexaferrite) powders were prepared by sol-gel processing. The produced powders were calcined at 550°C for 6 h and sintered at 1000°C for 5 h to obtain the required phases. The powders were characterized by differential thermal analysis/thermogravimetric analysis (DTA/TG), X-ray diffractometry (XRD) and scanning electron microscopy (SEM), and vibrating-sample magnetometry (VSM). The XRD patterns indicated that the pure barium ferrite phase was not obtained. The presence of M-type BaFe11.6Mn0.4O19 was confirmed in the Ferrite B and Ferrite D patterns. In the Ferrite C pattern, there were the phases of BaFe12O19, Ba2Cu2Fe12O22 (X or Z-type) and Sr3Fe2O6.16. The Ba0.5Sr0.5Fe12 phase was easily observed in the Ferrite E pattern. The results showed that the dopant materials significantly change the particle shape of Ferrite A powders, but also lower the value of the coercivity. A higher saturation magnetization was observed for the Ferrite D powder.

The density-functional theory (DFT) is used to simulate clusters of the formula FenAsm. We optimize the bond lengths and angles to determine the stable structure for integer values of n and m. We calculate the vibrational frequencies for all of the clusters and hence determine the largest frequency of each cluster as a function of number of As atoms. For

Several interesting experiments in the advanced laboratory require an accurate measurement of a slowly varying, extremely small voltage. Lock-in detection is a powerful technique to recover such a signal, even in the presence of broadband noise whose magnitude is several times greater than the signal itself. We have implemented a versatile, low-cost digital lock-in analyzer completely in software. No specialized

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