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Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al–Zn–Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of Tc ≅ 0:05 K. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: The natural boron has two kinds of isotopes which are existed 20 wt% boron-10 (10B) and 80 wt% boron-11 (11B).11B isotope is stable against the neutron irradiation without nuclear transformation. For an advanced fusion application, in-situ PIT process using 11B isotope powder as the boron source material was desirable to enhance low induced radio-activity of MgB2 superconducting wire. We tried to fabricate the in-situ Cu addition MgB2/Ta/Cu multifilamenatry wire using boron isotope powder as the boron source material. In this study, superconductivity and microstructure of MgB2 wire using boron isotope powder were investigated. Tc value of MgB2 wire using 11B powder was shown to about 37K by the low temperature diffusion reaction, and its value was higher than commercial natural powder. However, Jc value of MgB2 wire using 11B isotope powder was remarkably lower than that of commercial natural powder. This is caused by the forming of much impurity phase and decrease of MgB2 volume fraction due to the remaining of much non-reactive 11B isotope powder. [Copyright &y& Elsevier]

V3Ga compound has a shorter radioactive decay time compared with Nb-based compounds and it will be one of the candidate superconducting magnet materials for advanced low activation fusion reactor systems including shutdown scenario and material recycle. Recently, we succeeded in developing new V3Ga multifilamentary wires fabricated via the Powder In-Tube (PIT) process using high Ga content Cu-Ga binary phase compounds. We also found that high Ga content in the precursor promoted the formation of the stoichiometric V3Ga phase and it was effective in improving superconducting properties. [ABSTRACT FROM AUTHOR]

Research and development of Nb3Al strands and cables for a high field accelerator magnet is ongoing under the framework of the CERN-KEK collaboration. In this program, new Ta-matrix Nb3Al strands were developed and their mechanical properties and superconducting properties were studied. The non-Cu Jc values of these strands were 750\sim 800\ \A/mm^2 at 15 T and 4.2 K. Using these strands, test fabrication of 27-strand Rutherford cable was carried out in collaboration with NIMS and Fermilab. The properties of the strands extracted from the cable were examined and it was found that there was no degradation of the superconducting properties of the strands. In this paper, we report the fabrication of the strands and the cable in brief and present some of the results obtained by studying their properties. [ABSTRACT FROM AUTHOR]

Rapid heating, quenching and transformation (RHQT)-processed Nb3Al wires possess better strain tolerance than Nb3Sn wires. However, RHQT-processed Nb3Al wires so far developed show lower non-copper critical current density (Jc) than recently developed high-(Jc) Nb3Sn wires in the field range of 12-15 T. Therefore, the development of Nb3Al wires having enhancing Jc in this field range is a major concern for accelerator magnet designers. Among a number of fabrication parameters that might affect properties, we analysed the effect of thickness of Al and Nb foils in the jelly-roll-shaped filaments embedded in the precursor wires. Mechanical and superconducting properties of these wires with various Al-foil thicknesses in the filaments were investigated. [ABSTRACT FROM AUTHOR]

We present a muon-spin rotation study of the optimally doped cuprate superconductor (BiPb)2(SrLa)2 CuO6+ δ . The measured magnetic field dependence of the in-plane magnetic penetration λ ab suggests superconductivity with a dominant d-wave order parameter. The comparison of the temperature dependence of λ ab with calculations, assuming the angular gap symmetry as obtained from photoemission measurements, is consistent with a partial suppression of the quasi-particle weight towards the anti-nodal region of the Fermi surface. This suggests that the superconducting and the pseudogap state are dominated by different parts of the Fermi surface. [ABSTRACT FROM AUTHOR]

Abstract: We found that the length of the Fermi arc decreases with increasing out-of-plane disorder by performing angle resolved photoemission spectroscopy (ARPES) measurements in the superconducting state of optimally doped R=La and Eu samples of Bi2Sr2− x R x CuO y . Since out-of-plane disorder stabilizes the antinodal pseudogap as was shown in our previous study of the normal state, the present results indicate that this antinodal pseudogap persists into the superconducting state and decreases the Fermi arc length. We think that the shrinkage of the Fermi arc reduces the superfluid density, which explains the large suppression of the superconducting transition temperature when out-of-plane disorder is increased. [Copyright &y& Elsevier]

We attempted to reduce the matrix ratio down to 0.5 and 0.25 for RHQT (rapid-heating, quenching and transformation) Nb3 Al wires, which is directly related to improvement of the non-Cu Jc. The Ta matrix was chosen to improve the wire strength. It was found that the matrix ratio of 0.25 is too small to carry out RHQ treatment although drawing was possible by using cassette-roller dies (CRDs) as well as conical dies. The reduction of the matrix ratio down to 0.5 can also be achieved. However, the scale-up would make the drawing very difficult. It would be necessary for the scale-up to improve adhesion among the jelly-roll (JR) cores and also the outer Ta sheath in the multi-billet. The RHQ treatment was possible for the wire with a matrix ratio of 0.5. However, it was successful only when the wire diameter was less than 1.13 mm. It is necessary to suppress the experienced bend strain in the operation. The non-Cu Jc was found to be improved by about 20% by the reduction of the matrix ratio, compared to conventional Nb3Al wires. [ABSTRACT FROM AUTHOR]

Two Cu stabilized Nb3Al strands, F1 (Nb matrix) and F3 (Ta matrix), fabricated at NIMS were wound into Rutherford cables at Fermilab in collaboration with NIMS. A Small Race-track magnet using F! Rutherford cable, the first Nb3Al dipole magnet in the world, was constructed and tested to full current at Fermilab. This magnet was tested extensively to full short sample data and its quench characteristics were studied and reported. The 3-D magnetic field calculation was done with ANSYS to find the peak field. The quench characteristics of the magnet are explained with the characteristics of the Nb3 Al strand and Rutherford cable. The Small Racetrack magnet built using Ta matrix F3 strand was constructed and will be tested in the near future. The advantages and disadvantages of these Nb3Al cables are briefly discussed. [ABSTRACT FROM AUTHOR]

In the development of RHQT-processed Nb3Al wires for high-field accelerator magnet applications, one of the major objectives is to increase the non-copper critical current density in the field range of 12-15 T. To pursue this goal, a low-matrixratio wire was fabricated, and the effects of the RHQ conditions and the area reduction after the RHQ treatment on the properties of the wire were investigated. This paper describes the details and results of this study. [ABSTRACT FROM AUTHOR]

Characteristics of recently developed Nb3Al strand though the RHQT (rapid heating/quenching and transformation) process are described. One kilometer-long copper stabilized Nb3 Al round strands were economically fabricated with ion-plating and electroplating. The copper electroplating was successfully done with the high velocity of 5 m/h. A strong bonding between the copper and the precursor was achieved, and the mechanical rolling test did not show the separation of the copper stabilizer from the precursor. The rolled Nb3 Al strands showed no degradation both in critical current density and RRR value. Magnetic instability at 4.2 K at low fields was apparently improved on the recent F3 strand, relative to the previously F1 stand because a tantalum was used for the interfilament matrix of precursor. The large magnetic flux jumps, which were observed with the F! strand, were suppressed at 4.2 K, although appeared again below 3.0 K. The twisted strands are shown to be effective to reduce the time-dependent eddy current coupling. It was obtained 48 μm of Deff on F3 strand with twist pitch of 45 mm. In addition, the transverse pressure test for the F1 Nb3 Al strand was performed at 4.2 K and 12 T. The critical, current did not degrade with the transverse pressure up to 210 MPa. [ABSTRACT FROM AUTHOR]

In conventional superconductors, the superconducting gap in the electronic excitation spectrum prevents scattering of low-energy electrons. In high-temperature superconductors (HTSs), an extra gap, the pseudogap, develops well above the superconducting transition temperature TC. Here, we present a new avenue of investigating the pseudogap state, using scanning tunnelling microscopy (STM) of resonances generated by single-atom scatterers. Previous studies on the superconducting state of HTSs have led to a fairly consistent picture in which potential scatterers, such as Zn, strongly suppress superconductivity in an atomic-scale region, while generating low-energy excitations with a spatial distribution—as imaged by STM—indicative of the d-wave nature of the superconducting gap. Surprisingly, we find that similar native impurity resonances coexist spatially with the superconducting gap at low temperatures and survive virtually unchanged on warming through TC. These findings demonstrate that properties of impurity resonances in HTSs are not determined by the nature of the superconducting state, as previously suggested, but instead provide new insights into the pseudogap state. [ABSTRACT FROM AUTHOR]

The authors have been developing the Nb3Al conductors through transformation process, where the Nb3AL phase forms from the BCC (body-centered cubic) Nb(Al) supersaturated solid solution phase; the BCC phase is quenched by rapid-cooling from a temperature around 2000°C. It was reported several times that deformation to the quenched BCC Nb(AI) phase influences the superconducting properties, usually improving Jc. But, the results have not been discussed in detail so far from a metallurgical viewpoint. This work investigates the fundamental relationship between the BCC-deformation, transformation temperature, microstructure and superconducting properties. The transformation temperature is identified by DTA measurement, detecting the release of the free energy between the BCC and the Nb3Al phases. It was found that the transformation temperature has a tendency of monotonic decrease with the deformation. But, the transformation temperature does not seem to go down below a temperature of about 720°C even by strong deformation. The microstructures observed by FESEM suggests that the grain size is reduced almost proportionally with the deformation. In case of reduction in area of 99%, the grain size is reduced down to about 250 nm from 1.2 μm. The Jc increases with deformation, not showing a peak. The Jc of the wire (ME365) with reduction in area of 86% shows the best performance of the Nb3A1 wire ever reported. But, at least high-field Jc seems to saturate at a certain value. [ABSTRACT FROM AUTHOR]

To demonstrate the RHQT Nb3Al conductor to be really a candidate for a high-field magnet, we have fabricated 1 km-class Cu stabilized RHQT Nb3Al flat-wires, manufactured two insert real-sized coils #A and #B, and tested in a superconducting back-up field of 15 T at 4.2 K. Using the coil #A, a thinning of insulator, a winding technique, a new transformation annealing profile in a vacuum with a fast temperature-ramp above 500°C, decarbonization, an impregnation technique used for the Nb3Sn coil were preliminarily checked to be no matter. The coil #B that was wound with a 764 m piece could produce an additional 4.5 T (total 19.51) at 4.2 K in a clear bore of 30 mm without any training, when the coil current achieved the Ic of short samples that were simultaneously transformation annealed with the coil #B. [ABSTRACT FROM AUTHOR]

Recent studies of RHQ-processed Nb3Al wires for future accelerator magnets are presented and discussed. Test wires were prepared with different fabrication parameters, such as the Nb matrix ratio, RHQ current, area reduction ratio of the wire after an RHQ treatment and the 2nd heat treatment condition. Measurements of the critical current density (Jc) and n-value have been performed during the past several years. Recently, we performed the critical temperature (Tc) measurement, and the relationship between Jc and Tc was investigated by an RHQ treatment, a 2nd heat treatment, the Nb matrix ratio, and the area reduction effect. [ABSTRACT FROM AUTHOR]

Tightly shrunk Sn-Ta ingots with good workability were prepared by the reaction at 750°C–800°C from the mixed powder of Sn and Ta containing 25–30at%Ta. Then Jelly Roll processed wires were fabricated starting from Sn-Ta/Nb composites in which thick (Nb, Ta)3Sn layers were produced after the heat treatment. A few wt% Cu addition to the Sn-Ta mixed powder reduces the heat treatment temperature. Moreover, a few at% Ti substitution for Sn + Ta enhances the formation of (Nb, Ta)3Sn layer, and improves the non-Cu Jc of the wire. In the present study, effect of the Sn-Ta-Ti-Cu sheet composition on the structure and high-field performance of the wire has been studied. It has been found that a small amount of Ti and Cu addition decreases the amount of Ta in the sheet from 25–30at% to 10at%, which is favorable for the material cost reduction. Moreover, it has been revealed that thick (Nb, Ta)3Sn layers are synthesized even if the Cu concentration in the sheet is decreased less than lwt% when a few at% Ti is substituted. A non-Cu Jc of ∼ 150 A/mm2 has been obtained at 22 T and 4.2 K in the wires with different sheet composition after the heat treatment at 725°–750°C. [ABSTRACT FROM AUTHOR]

Feasibility study of Cu stabilized Nb3AI strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb3A1 strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A/mm² at 15 Tesla at 4.2 K, a copper content of 50%, and filament size of about 50 microns. Rutherford cables with 27 Nb3Al strands of 1.03 mm diameter were fabricated and tested. Quench tests on a short cable were done to study its stability with only its self field, utilizing a high current transformer. A pair of 2 meter long Nb3Al cables was tested extensively at CERN at 4.3 and 1.9 K up to 11 Tesla including its self field with a high transport current of 20.2 kA. In the low field test we observed instability near splices and in the central region. This is related to the flux-jump like behavior, because of excessive amount of Nb in the Nb3Al strand. There is possibility that the Nb in Nb3Al can cause instability below 2 Tesla field regions. We need further investigation on this problem. Above 8 Tesla, we observed quenches near the critical surface at fast ramp rate from 1000 to 3000 A/sec, with quench velocity over 100 m/sec. A small racetrack magnet was made using a 14 m of Rutherford cable and successfully tested up to 21.8 kA, corresponding to 8.7 T. [ABSTRACT FROM AUTHOR]

Abstract: Three kinds of stabilized rapid-heating, quenching and transformation annealing (RHQT) Nb3Al round wires have been developed for nuclear fusion devices; the Ag internally stabilized Nb matrix, the Cu internally stabilized Ta matrix and Cu ion-plated/electroplated wires. The critical current densities J c of Nb3Al filaments are almost the same as the conventional Cu clad stabilized flat-wire, as long as the J c is optimized by mechanical deformation of wire after quenching but before the final transformation annealing. To demonstrate the applicability of RHQT Nb3Al wire to nuclear fusion devices, we have trial manufactured a cable-in-conduit conductor (CICC) using the Ag internally stabilized round strands and confirmed the critical current of CICC to be nearly the same with the strain-free designed one. [Copyright &y& Elsevier]

Recent developments in RHQ Nb3A1 wire for accelerator magnets are presented and discussed. The main items of the development are to increase the critical current density (Jc) and to find a good stabilization method. For the former item, test wires with different Nb-matrix/filament ratios were made, and the effect of the ratio on Jc was investigated in correlation with the heat treatment and the area reduction after the RHQ process. For the latter item, a special copper electroplating technique was developed to deposit a thick C u layer on the surface of the wire. The mechanical bonding strength and the electrical characteristics of the Cu layer were studied by bending and drawing the wire, and by measuring the resistance. Although the present piece length of the C u stabilized Nb3A1 wire is about 40 cm, we can draw and reduce the wire down to 60% of the original diameter, without breaking the wire or damaging the bonding of the Cu stabilizer. The highest noncopper Jc achieved during this study was 2156 A/mm² at 10 T and 4.2 K. [ABSTRACT FROM AUTHOR]

We have studied about annealing effect on V-based Laves phase compound multifilamentary superconducting wire using the Rapidly Heating and Quenching (RHQ) process in order to improve superconducting property. We found that the reaction layer within 10 microns was formed between powder mixture filament and V matrix after the RHQ process. The transport Jc values of samples post-annealed at 600°C for 10 hours were increased remarkably compared with as-quenched samples, and then Hc2 value calculated by Kramer's formula was increased from 14 T to 16 T by additional annealing. In this paper, the post-annealing condition effect on both microstructure and Jc-B property of V-based Laves phase compound superconductor made through RHQ process was investigated. [ABSTRACT FROM AUTHOR]

The replacement of Nb matrix with Ta for rapid-heating, quenching and transformation annealing (RHQT) processed Nb3Al conductor seems to be advantageous for facilitating the RHQ operation due to a higher mechanical strength at elevated temperatures and less reactivity with the molten Ga in the quench bath and suppressing flux jumps in low magnetic fields. We have fabricated three grades of the Ta matrix precursor, in which the volume fraction of Ta matrix is different, so as to examine the drawability of such Ta matrix precursors. Also examined are the effects of using the Ta matrix on the RHQ condition, Tc values after quenching and subsequent annealing, respectively, Jc (core), overall residual resistivity, and magnetization curves. We have succeeded in drawing all of Ta matrix precursors and confirmed the favorable existence of a plateau region in the IRHQ - Tc relationship even for the Ta matrix RHQT Nb3Al conductors. The resulting superconducting properties were comparative to those of Nb matrix conductors. The replacement of Nb matrix with Ta was very effective in suppressing flux jumps even at 4.2 K. [ABSTRACT FROM AUTHOR]

The bcc supersaturated solid solution, Nb(Al)ss obtained by rapid heating and quenching of a multifilamentary Nb/Al composite wire has shown a change from a disordered to an ordered structure before finally transforming to the A15 Nb3Al phase. It is believed that such ordering is responsible for suppressing the critical temperature, Tc, the upper critical magnetic field, Bc2, and the critical current density, Jc. The ordering of the bcc phase can be suppressed by increasing the heating rate, and therefore this should improve the superconducting properties of the resulting Nb3Al wires. Enhancement of Jc can also be achieved if the Nb(Al)ss phase is mechanically deformed before transformation. The transformation process was studied in as-quenched and mechanically deformed Nb/Nb(Al)ss wires by in-situ resistance measurement under heating at two different rates, 200°C/h and 800°C/h. The electrical resistivities of the wires decrease abruptly during the transformation from bcc to A15 phases and the process is much faster for mechanically deformed wires. Also, the healing rate affects the onset temperature of the A15 transformation. The results also show that the Jc of the transformed Nb3Al wires increases with increasing reduction in area. [ABSTRACT FROM AUTHOR]

Whereas Nb3Sn wires are commercially available and produced in long lengths for the fabrication of large high field magnets, Nb3Al is emerging as a candidate material for even higher fields, particularly for nuclear fusion devices. We are therefore investigating the basic superconducting parameters of both materials, such as the transition temperature, the critical current densities and the upper critical fields, as a function of gamma dose and fast neutron fluence. Whereas the transition temperature of these multifilamentary wires is found to decrease slightly, both Jc and the upper critical fields (as determined from Kramer plots) increase with neutron fluence, in agreement with previous work on A15 systems. The enhancement of the critical currents amounts to approximately 15%. Further irradiation work to higher fluences is under way, in order to investigate the limits of these materials for applications in a radiation environment. [ABSTRACT FROM AUTHOR]

We tried to enlarge a Nb/Al strand dimension to enhance a current capacity of RHQT-Nb3AI further, So far good fsRHQ operation could be made by using the strand dimension of less than ø 1.35 mm. This time we tried to make RHQ operation by using a Nb/Al rectangular strand of 1.45 × 2.2 mm2 which is double cross-section area of ø 1.35 mm. Bcc phases could he formed even in the large cross-section rectangular strand by RHQ operation. The samples were post-annealed at 800° C for transforming into A15. The resultant Ic and core Jc were 232.5 A and 130 A/mm2 at 4.2 K, 22 T, respectively. These values largely surpassed Ic of 57.5 A and Jc of 72.7 A/mm2 at 4.2 K, 22 T for the sample which was made by using a conventional ø 1.35 mm strand. [ABSTRACT FROM AUTHOR]

We have examined the critical current Ic and n-values of RHQT processed Nb3Al conductors at 4.2 K in a wide range of fields from 14.5 to 25 T in relation to the microstructures obtained. For a point and a tail of Cu-clad rectangular conductor used for a winding, the n-values were determined by fitting the voltage over a taps spacing of 110 or 220 mm to a relationship of V = CIn, in a range from 10-5 to 10-4 V/m. Such n-values were almost the same with each other, indicating the uniformity of a 370 m length of RHQT Nb3Al conductor as the Ic consistency does. The n-value increased monotonously with decreasing a field from 25 T to 18 T, but got saturated to be around 35 at 4.2 K in fields less than 18 T. The n-value at 21 T and 4.2 K, corresponding to 23.5 T and 1.8 K, was about 25, and confirmed to be large enough for NMR uses. [ABSTRACT FROM AUTHOR]

Studies the superconducting properties and rapid heating condition in transformed jelly-roll Nb[sub 3]Al multifilamentary superconducting wire. Critical temperature and magnetization properties; Temperature rise during rapid heating; Critical current density as a function of annealing time.

Multifilamentary Nb/sub 3/Al superconducting wires for high field magnets above 20 T have been developed by a rapid-quenching process. A long length wire was produced, and a coil was fabricated using the wire. J/sub c/ of this wire was 195A/mm/sup 2/ at 20 T, 4.2 K and 486A/mm/sup 2/ at 20 T, 1.8 K, B/sub c2/ of the coil was 24.6 T at 4.2 K and 26.9 T at 1.8 K and the T/sub c/ was 17.8 K. In addition to investigating the stability, the residual resistance ratio was measured, the value was 16.9. Scattering of J/sub c/ in the longitudinal direction was examined and found to be within /spl plusmn/10%. [ABSTRACT FROM PUBLISHER]

A complicating factor in unravelling the theory of high-temperature (high-\(T_c\)) superconductivity is the presence of a ‘pseudogap’ in the density of states, the origin of which has been debated since its discovery. Some believe the pseudogap is a broken symmetry state distinct from superconductivity whereas others believe it arises from short-range correlations without symmetry breaking. A number of broken symmetries have been imaged and identified with the pseudogap state, but it remains crucial to disentangle any electronic symmetry breaking from the pre-existing structural symmetry of the crystal. We use scanning tunnelling microscopy to observe an orthorhombic structural distortion across the cuprate superconducting \(Bi_{2}Sr_{2}Ca_{n−1}Cu_{n}O_{2n+4+x}\) (BSCCO) family tree, which breaks two-dimensional inversion symmetry in the surface BiO layer. Although this inversion-symmetry-breaking structure can impact electronic measurements, we show from its insensitivity to temperature, magnetic field and doping, that it cannot be the long-sought pseudogap state. To detect this picometre-scale variation in lattice structure, we have implemented a new algorithm that will serve as a powerful tool in the search for broken symmetry electronic states in cuprates, as well as in other materials., Physics, Other Research Unit

Abstract: Specific heat measurements were performed on a high-quality single crystal of . Peaks at the superconducting transition temperature and the antiferromagnetic transition temperature indicate sharp transitions compared to our previous data. The temperature dependence of specific heat below 0.3K is well described by the equation of with and , evidencing line nodes in the superconducting gap. [Copyright &y& Elsevier]

Abstract: Magnetism and superconductivity in the heavy-fermion superconductor have been studied under pressure. The antiferromagnetic and superconducting transition temperatures, and , respectively, decrease by applying pressure. becomes zero around 0.6–0.7GPa, while the pressure dependence of exhibits a shoulder-like feature around 0.7GPa, and superconductivity is found to persist in the pressure range up to about 1.5GPa. A broad peak around 5K in the temperature derivative of thermal expansion and electrical resistivity at ambient pressure begins to shift to higher temperatures above 0.7GPa. These results suggest that a critical pressure exists around 0.6–0.7GPa in . [Copyright &y& Elsevier]

Abstract: Magnetic and superconducting properties have been investigated on a single crystal of CePt3Si which is the recently discovered heavy-fermion superconductor. The effect of magnetic field on the antiferromagnetic transition temperature was studied by the iso-field thermal expansion coefficient. From these results, together with the results of the electrical resistivity under magnetic fields, magnetostriction and magnetization measurements, we have constructed the magnetic and superconducting phase diagrams for and [001]. [Copyright &y& Elsevier]

Abstract: We have studied how the phase diagram of the Bi2Sr2−x R x CuO y system depends on the rare earth element R. The angle-resolved photoemission spectroscopy (ARPES) measurement revealed that the pseudogap is larger for the R =Eu sample than the R =La sample when compared at the same carrier concentration while the transition temperature T c of the R =La sample is larger. This implies that changing the R element to one with a smaller ionic radius stabilizes the pseudogap phase and suppresses at the same time the high-T c superconducting phase. [Copyright &y& Elsevier]

A correction to the article "Visualization of the interplay between high-temperature superconductivity, the pseudogap and impurity resonances" that was published in the 2008 issue is presented.

The unclear relationship between cuprate superconductivity and the pseudogap state remains an impediment to understanding the high transition temperature (Tc) superconducting mechanism. Here, we used magnetic field-dependent scanning tunneling microscopy to provide phase-sensitive proof that d-wave superconductivity coexists with the pseudogap on the antinodal Fermi surface of an overdoped cuprate. Furthermore, by tracking the hole-doping (p) dependence of the quasi-particle interference pattern within a single bismuth-based cuprate family, we observed a Fermi surface reconstruction slightly below optimal doping, indicating a zero-field quantum phase transition in notable proximity to the maximum superconducting Tc. Surprisingly, this major reorganization of the system's underlying electronic structure has no effect on the smoothly evolving pseudogap. [ABSTRACT FROM AUTHOR]

We have studied the momentum dependence of the energy gap of Bi2(Sr,R)2CuOy by angle-resolved photoemission spectroscopy (ARPES), particularly focusing on the difference between R=La and Eu. By comparing the gap function and characteristic temperatures between the two sets of samples, we show that there exist three distinct energy scales, Δpg, Δsc0, and Δsc0eff, which correspond to T* (pseudogap temperature), Tonset (onset temperature of fluctuating superconductivity), and Tc (critical temperature of coherent superconductivity). The results not only support the existence of a pseudogap state below T* that competes with superconductivity, but also the duality of competition and superconducting fluctuation at momenta around the antinode below Tonset. [ABSTRACT FROM AUTHOR]

Abstract: The heavy fermion state in the f-electron systems is due to competition between the RKKY interaction and the Kondo effect. The typical compound is . To understand the electronic state, we studied the Fermi surface properties via the de Haas–van Alphen (dHvA) experiment and energy band calculation for , and nowadays, transuranium compounds. Pressure is also an important technique to control the electronic state. The Néel temperature decreases with increasing pressure P and becomes zero at the critical pressure for . The typical compound is an antiferromagnet , which we studied from the dHvA experiment under pressure. A change of the 4f-electronic state from localized to itinerant is realized at , revealing the first-order phase transition, together with a divergent tendency of the cyclotron mass at . It is stressed that appearance of superconductivity in is closely related to the heavy fermion state. It is also noted that the parity-mixed novel superconducting state might be realized in a pressure-induced superconductor without inversion symmetry in the crystal structure. [Copyright &y& Elsevier]

We present a muon-spin rotation study of the optimally doped cuprate superconductor (BiPb)2(SrLa)2 CuO6+ δ . The measured magnetic field dependence of the in-plane magnetic penetration λ ab suggests superconductivity with a dominant d-wave order parameter. The comparison of the temperature dependence of λ ab with calculations, assuming the angular gap symmetry as obtained from photoemission measurements, is consistent with a partial suppression of the quasi-particle weight towards the anti-nodal region of the Fermi surface. This suggests that the superconducting and the pseudogap state are dominated by different parts of the Fermi surface. [ABSTRACT FROM AUTHOR]

Abstract: Revolution of the pressure-induced heavy fermion state and superconductivity in an antiferromagnet CeRhIn5 have been established by high-pressure Fermi surface studies using the de Haas–van Alphen technique. A marked change of the 4f-electron nature from localized to itinerant is realized at a critical pressure under magnetic fields, together with a divergent tendency of the cyclotron mass at . The electronic state of CeIrSi3 with the non-centrosymmetric tetragonal structure is also tuned from the antiferromagnetic state to the superconducting state as a function of pressure. The upper critical field at pressure of 2.65GPa is found to be highly anisotropic: for and for , with the superconducting transition temperature . A large magnitude of and a large anisotropy of are characteristic, which reveals a new type of superconductivity closely related to the spin–orbit interaction based on the non-centrosymmetric crystal structure. [Copyright &y& Elsevier]

Abstract: Magnesium diboride (MgB2) superconducting wires are interesting as alternative conductor of Nb-based superconducting wire applying for the advanced nuclear fusion reactor from viewpoint of decay time of induced radioactivity. However, J c property of MgB2 wire is insufficient for alternative material of Nb-based superconductor, and it is necessary to improve further J c property. In order to improve J c property, we tried to fabricate the several trace amounts of Cu addition MgB2/Fe-sheathed wires through PIT process using Mg2Cu as Cu addition source. T c values of Cu addition samples were higher than those of non-Cu addition samples and they were improved with increasing amount of Cu addition. On the other hand, core J c value were decreased with increasing amount of Cu addition and the maximum core J c values were estimated to be over 100A/mm2 at 4.2K under 8T for 1 and 3at% Cu addition sample. [Copyright &y& Elsevier]

MgB2 can be synthesized through a new route using Mg2Cu instead of pure Mg. When the temperature is elevated to around the melting point of Mg2Cu (568 °C), the Tc for Mg2Cu/B Fe-sheathed wires increases rapidly to about 37.5 K. Mg2Cu with its low melting point promotes the diffusion reaction to form a high Tc MgB2 at low temperatures. A lot of second phases forms with small amounts of MgB2 in the core of the wires. However, the transport Jc value, which is greater than 105 A/cm2 at 4.2 K in ambient fields, is rather high. Since the Jc value is estimated from a net-cross-sectional area of MgB2 it is expectedly high. Moreover, Mg2 Cu/B/metal-substrate layered composites were also prepared in this study. After a heat treatment at 600 °C for 10 h in a vacuum, a 50 μm thick MgB2 diffusion layer forms with a high-density microstructure. Cu is released from Mg2Cu, and collects on the surface of the diffusion layer. This behavior of Cu is similar to that of the bronzed process used for Nb3 Sn practical conductors. [Copyright &y& Elsevier]

Abstract: We measured the electrical resistivity in antiferromagnets (a Néel temperature ) and (, ) under pressure. In , superconductivity was found in a wide pressure region from 1.8GPa to about 3.5GPa, where the superconducting transition temperature is at a critical pressure at which the Néel temperature becomes zero. On the other hand, the antiferromagnetic ordering of is stable up to 8GPa. [Copyright &y& Elsevier]

Abstract: We investigated the magnetic properties of (T: Ru, Os, Co, Rh, Ir, Pd and Pt) and (T: Co, Rh and Ir) by measuring their electrical resistivity and magnetic susceptibility. , and do not order magnetically, with a large Kondo temperature of about . The other compounds order antiferromagnetically, and are very similar to each other in their magnetic and electronic properties, which is related to a large crystalline electric field (CEF) splitting energy of the electron, about in . [Copyright &y& Elsevier]

Abstract: We have determined the pressure-temperature phase diagram of heavy-fermion superconductor by the AC heat capacity measurement. The Néel temperature decreases with increasing pressure and becomes zero at the critical pressure . On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to about 1.5GPa. The phase diagram of is thus very unique and has never been reported before for other heavy fermion superconductors. [Copyright &y& Elsevier]