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Topological superconductors have long been predicted to host Majorana zero modes which obey non-Abelian statistics and have potential for realizing non-decoherence topological quantum computation. However, material realization of topological superconductors is still a challenge in condensed matter physics. Utilizing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations, we predict and then unveil the coexistence of topological Dirac semimetal and topological insulator states in the vicinity of Fermi energy (EF) in the titanium-based oxypnictide superconductor BaTi2Sb2O. Further spin-resolved measurements confirm its spin-helical surface states around EF, which are topologically protected and give an opportunity for realization of Majorana zero modes and Majorana flat bands in one material. Hosting dual topological states, the intrinsic superconductor BaTi2Sb2O is expected to be a promising platform for further investigation of topological superconductivity. [ABSTRACT FROM AUTHOR]

In this paper, we systematically studied Ca-YBCO and CaLa-YBCO systems by Raman spectroscopy. It is found that is closely related to the vibration of lattice. In the Ca-YBCO system, the phonons around 115 and 335 cm harden as the decreases. Oppositely, the 140 cm mode and the 220 cm mode soften. In the CaLa-YBCO system, the decreases gradually with the content of Ca and La. The Raman peak of 140 cm mode hardens and the 360 cm mode softens. Besides, the fluctuations of phonons of 210 cm mode and 575 cm mode were observed. [ABSTRACT FROM AUTHOR]

200 keV Cu+ ions were implanted into 6H-SiC single crystal at room temperature with fluence of 8 × 1015 cm-2. No ferromagnetism (FM)-related secondary phase was found by the results of high-resolution x-ray diffraction and x-ray photoelectron spectroscopy. Positron annihilation lifetime spectroscopy results indicated that the main defect type was silicon vacancy and the concentration of it increased after Cu implantation. The room-temperature ferromagnetism was detected by superconducting quantum interference device. First-principles calculations revealed that the magnetic moments mainly come from the 2p orbitals of C atoms and 3d orbitals of Cu dopant. The origin of the FM has been discussed in detail. [ABSTRACT FROM AUTHOR]

Superconductors are known for the ability to trap magnetic field. A thermally actuated magnetization (TAM) flux pump is a system that utilizes the thermal material to generate multiple small magnetic pulses resulting in a high magnetization accumulated in the superconductor. Ferrites are a good thermal material candidate for the future TAM flux pumps because the relative permeability of ferrite changes significantly with temperature, particularly around the Curie temperature. Several soft ferrites have been specially synthesized to reduce the cost and improve the efficiency of the TAM flux pump. Various ferrite compositions have been tested under a temperature variation ranging from 77K to 300K. The experimental results of the synthesized soft ferrites—Cu0.3Zn0.7Ti0.04Fe1.96O4, including the Curie temperature, magnetic relative permeability and the volume magnetization (emu/cm3), are presented in this paper. The results are compared with original thermal material, gadolinium, used in the TAM flux pump system. Cu0.3Zn0.7Ti0.04Fe1.96O4 holds superior characteristics and is believed to be a suitable material for next generation TAM flux pump. [ABSTRACT FROM PUBLISHER]

High-temperature superconductors have created the opportunity for a step change in the technology of power applications. Racetrack superconducting coils made from YBCO coated conductors have been used in several engineering applications including SMES, rotor or stator windings of electric machines. AC loss is one of the most important factors that determine the design and performance of superconducting devices. In this paper, a numerical model is developed to calculate the AC losses in superconducting racetrack coils in different magnetic conditions. This paper first discusses the AC losses of the coils in self-field or external field only. It then goes to investigate the AC losses of the coils being exposed to AC ripple field and a DC background field. Finally, the AC losses of the coils carrying DC current and being exposed to AC field are calculated. These two scenarios correspond to using superconducting coils as the rotor field winding of an electric machine. [ABSTRACT FROM AUTHOR]

High Temperature superconductors are able to carry very high current densities, and thereby sustain very high magnetic fields. There are many projects which use the first property and these have concentrated on power generation, transmission and utilization, however there are relatively few which are currently exploiting the ability to sustain high magnetic fields. There are two main reasons for this: high field wound magnets can and have been made from both BSCCO and YBCO but currently their cost is much higher than the alternative provided by low Tc materials such as Nb3Sn and NbTi. An alternative form of the material is the bulk form which can be magnetized to high fields and using flux pumping this can be done in situ. This paper explores some of the applications of bulk superconductors and describes methods of producing field patterns using the highly uniform magnetic fields required for MRI and accelerator magnets as the frame of reference. The patterns are not limited to uniform fields and it is entirely possible to produce a field varying sinusoidally in space such as would be required for a motor or a generator. The scheme described in this paper describes a dipole magnet such as is found in an accelerator magnet. The tunnel is 30\times 50\times 1000\ mm and we achieve a uniformity of better than 200 ppm over the 1000 mm length and better than 1 ppm over the central 500 mm region. The paper presents results for both the overall uniformity and the integrated uniformity which is 302 ppm over the 1000 mm length. [ABSTRACT FROM AUTHOR]

A novel technique is proposed to magnetize bulk superconductors, which has the potential to build up strong superconducting magnets. Instead of conventionally using strong magnetic pulses, periodical magnetic waves with strength as low as that of rare-earth magnets are applied. These magnetic waves travel from the periphery to the center of a bulk superconductor and become trapped little by little. In this way, bulk superconductors can gradually be magnetized. To generate these magnetic waves, a thermally actuated magnet was developed, which is constructed by a heating/cooling switch system, a rare-earth bulk magnet, and a Gadolinium (Gd) bulk. The heating/cooling switch system controls the temperature of the Gd bulk, which, along with the rare-earth magnet underneath, can transform thermal signals into magnetic waves. The modeling results of the thermally actuated magnet show that periodical magnetic waves can effectively be generated by applying heating and cooling pulses in turn. A YBCO bulk was tested in liquid nitrogen under the magnetic waves, and a notable accumulation of magnetic flux density was observed. [ABSTRACT FROM AUTHOR]

This paper presents an SMES coil which has been designed and tested by University of Cambridge. The design gives the maximum stored energy in the coil which has been wound by a certain length of second-generation high-temperature superconductors (2G HTS). A numerical model has been developed to analyse the current density and magnetic field distribution and calculate the AC losses during the charge and discharge process of the coil. A cryostat has been designed and a test of the I-V curve measurement of the coil has been accomplished. In addition, the power electronics control of the SMES coil has been simulated. [ABSTRACT FROM AUTHOR]

Magnets made from bulk YBCO are as small and as compact as the rare earth magnets but potentially have magnetic flux densities orders of magnitude greater than those of the rare earths. In this paper a simple technique is proposed for magnetizing the superconductors. This technique involves repeatedly applying a small magnetic field which gets trapped in the superconductor and thus builds up and up. Thus a very small magnetic field such as one available from a rare earth magnet can be used to create a very large magnetic field. This technique which is applied using no moving parts is implemented by generating a traveling magnetic wave which moves across the superconductor. As it travels across the superconductor it trails flux lines behind it which get caught inside the superconductor. With each successive wave more flux lines get caught and the field builds up and up. The wave could be generated in many different ways but the preferred way is simply to heat a material whose permeability changes with temperature at its edge. As the heat travels across the material so the permeability changes and a magnetic wave is generated. It is in effect the first novel heat pump in a very long time and one which will enable the enormous potential available from these unique and highly versatile superconducting magnets to be fully realized. Within this paper we present results showing the superconductor being progressively magnetized by sequentially applied "heat" pulses. We also demonstrate that the sign of the magnetization is reversed if "cold" pulses are applied instead of heat pulses. These experimental results are supported by modeling. [ABSTRACT FROM AUTHOR]

Bi-based superconducting phases have been studied by transmission electron microscopy. The strong one-dimensional modulations in undoped and Ce-doped monoclinic Bi2 Sr2 CuO6 (2201) samples are different from one another. We have found a new 2201 phase containing Pb and Ca with orthorhombic symmetry in nominal (Bi0.90 Pb0.10 )2 Sr2 CaCu2 O8 crystals. Its structure with space group Bbmb and two-dimensional modulation are analogous to those of the Pb-doped higher members of the structural series Bi2 Sr2 Can-1 Cun O2n+4 . Hence, this new orthorhombic rather than the monoclinic 2201 phase should be the first member of the structural series. [ABSTRACT FROM AUTHOR]

A unique structure, a network of nanotwins, is revealed for the first time in high-energy ion-irradiated YBa[sub 2] Cu[sub 3] O[sub 7-delta] . This structure is shown to form only at ion doses of 1011 cm-2 or greater and thus is not revealed in any earlier electron microscopy studies. In this higher-dose regime, the well known columnar defects are connected by the nanotwin structure, thus affecting bulk superconducting properties. Consequences for a number of published interpretations of such measurements related to pinning and dynamics of magnetic vortices are discussed. [ABSTRACT FROM AUTHOR]

We measured the resistivity and magnetic susceptibility to map out the phase diagram of single crystalline NaFe1-xCoxAs. Replacement of Fe by Co suppresses both the structural and magnetic transitions; however, it also enhances the superconducting transition temperature (Tc) and superconducting component fraction. Magnetic susceptibility exhibits temperature-linear dependence in high temperatures up to 500 K for all the superconducting samples, but such behavior suddenly breaks down for the nonsuperconducting overdoped crystal, suggesting that the superconductivity is closely related to the T-linear dependence of susceptibility. Analysis on the superconducting-state specific heat of the optimally doped crystal provides strong evidence for a two-band s-wave order parameter with gap amplitudes of &Dgr;1(0)/kBTC = 1.78 and &Dgr;2(0)/kBTC = 3.11, being consistent with the nodeless gap symmetry revealed by angle-resolved photoemission spectroscopy experiment. [ABSTRACT FROM AUTHOR]

Sizable single-crystalline samples of Ca10(Pt3As8)((Fe1-x:Ptx)2As2)5 (the 10-3-8 phase) with 0 ≤ x < 0.1 have been grown and have been systematically characterized via x-ray diffraction, magnetic, and transport measurements. The unsubstituted sample is a heavily doped semiconductor with no sign of magnetic order down to 2 K. With increasing Pt content, the metallic behavior appears, and superconductivity is realized for x ≥ 0.023. Tc rises to its maximum of approximately 13.6 K at the doping level of x ∼ 0.06f and then decreases for higher x values. The electronic phase diagram of the 10-3-8 phase was mapped out based on the magnetic and transport measurements. The mass anisotropy parameter &Ggr; ∼ 10, obtained from resistive measurements in magnetic fields, indicates a relatively large anisotropy in the iron-based superconductor family. This strong two-dimensional character may lead to the absence of magnetic order. A linear T dependence of susceptibility at high temperatures is observed, indicating that spin fluctuations exist in the underdoped region as in most of the Fe-pnictide superconductors. [ABSTRACT FROM AUTHOR]

We measured the transport properties and susceptibility of single-crystal Ca1-xLaxFe2As2 (x = 0, 0.05, 0.1, 0.15, 0.19, and 0.25). Large in-plane resistivity anisotropy similar to that in Co-doped 122 iron pnictides is observed although no transition metals were introduced in the FeAs plane. The in-plane resistivity anisotropy gradually increases with La doping below TSDW, being different from the hole-doped 122 superconductors. The susceptibilities of the samples show that La doping leads to suppression of the spin-density wave (SDW) and induces a Curie-Weiss-like behavior at low temperature, which is much stronger than the other 122 iron-based superconductors. [ABSTRACT FROM AUTHOR]

We successfully synthesized two new compounds, RbxFe2-yS2 and CsxFe2-yS2, which are isostructural with a KxFe2-ySe2 superconductor. We systematically investigated the resistivity, magnetism, and thermoelectric power of AxFe2-yS2 (A=K, Rb, and Cs) single crystals. High-temperature resistivity and magnetic measurements show anomalies above 500 K depending on A which are similar to AxFe2-ySe2. A discrepancy between zero-field-cooling (ZFC) and field-cooling (FC) curves was observed in KxFe2-yS2 and RbxFe2-yS2, whereas it disappears in CsxFe2−yS2. Our results indicate similar magnetism between AxFe2−yS2 and AxFe2−ySe2 at high temperature. [ABSTRACT FROM AUTHOR]

The mixed-metal-network layered compound TaFe1+xTe3 has the TaFeTe3 layers formed by Ta-Fe bonded network (Fe1) sandwiched with tellurium layers and the excess iron atoms (Fe2) partially occupying the interstitial site of the tetrahedral (Ta,Fe)Te at random, which are similar to the interstitial iron atoms in the iron-based high-Tc, superconductor Fe1+xTe. The antiferromagnetic (AFM) transition of Fel zigzag chains and spin flop of these interstitial Fe2 atoms under a high magnetic field are studied through susceptibility, magnetoresistance (MR), the Hall effect, and specific heat measurements in high-quality single-crystal TaFe1+yTe3. These properties suggest that the high-temperature AFM transition of the TaFeTe3 layers should be a spin-density-wave-type AFM order. Below TN, the spin flop of these interstitial Fe2 from antiferromagnetism to ferromagnetism induces a sharp drop on resistivity and an anomalous Hall effect. It can be inferred from the spin flop of Fe2 that the local moment of Fe2 atom is about 4 μB/Fe. The possible magnetic structure of TaFe1+yTe3 is proposed from the susceptibility, MR, and Hall effect. The properties related to the spin flop of Fe2 supply a good opportunity to study the coupling between Fe1 and Fe2 in these TaFe1+yTe3 or Fe1+yTe compounds with interstitial Fe2. [ABSTRACT FROM AUTHOR]