High Critical Temperature Superconductors Research Articles

Superconducting magnetic energy storage and superconducting self-supplied electromagnetic launcher

Superconductors can be used to build energy storage systems called Superconducting Magnetic Energy Storage (SMES), which are promising as inductive pulse power source and suitable for powering electromagnetic launchers. The second generation of high critical temperature superconductors is called coated conductors or REBCO (Rare Earth Barium Copper Oxide) tapes. Their current carrying capability in high magnetic field and their thermal stability are expanding the SMES application field. The BOSSE (Bobine Supraconductrice pour le Stockage d’Energie) project aims to develop and to master the use of these superconducting tapes through two prototypes. The first one is a SMES with high energy density. Thanks to the performances of REBCO tapes, the volume energy and specific energy of existing SMES systems can be surpassed. A study has been undertaken to make the best use of the REBCO tapes and to determine the most adapted topology in order to reach our objective, which is to beat the world record of mass energy density for a superconducting coil. This objective is conflicting with the classical strategies of superconducting coil protection. A different protection approach is proposed. The second prototype of the BOSSE project is a small-scale demonstrator of a Superconducting Self-Supplied Electromagnetic Launcher (S3EL), in which a SMES is integrated around the launcher which benefits from the generated magnetic field to increase the thrust applied to the projectile. The S3EL principle and its design are presented.

Spin and charge excitations in artificial hole- and electron-doped infinite layer cuprate superconductors

The asymmetry between electron and hole doping in high critical-temperature superconducting (HTS) cuprates is key information for the understanding of Cooper pair formation mechanisms. Despite intensive studies on different cuprates, a comprehensive description of related magnetic and charge excitations is still fragmentary. In the present work, artificial cuprates were used to cover the entire phase diagram within the same HTS family. In particular, Cu ${L}_{3}$-edge resonant inelastic x-ray scattering (RIXS) measurements were performed on artificial $n$- and $p$-type infinite layer (IL) epitaxial films. Beside several similarities, RIXS spectra show noticeable differences in the evolution, with doping level, of magnetic and charge intensity and damping. Compatible trends can be found in spectra measured on bulk cuprates, as well as in theoretical calculations of the spin dynamical structure factor $S(\mathbf{q},\ensuremath{\omega})$. The findings give a deeper insight into the evolution of collective excitations across the cuprate phase diagram, and on underlying general features, only connected to the doping type. Moreover, they pave the way to the exploration of general properties of HTS physics over a broad range of conditions, by means of artificial compounds not constrained by the thermodynamic limitations governing the chemical stability of bulk materials.

鉄系超伝導体の薄膜成長とデバイス作製

Iron-based superconductors have been receiving much attention as a new family of high-critical temperature superconductors since 2008 owing to their unique properties and distinct difference from cuprates and conventional superconductors. This paper reviews our research on iron-based superconductors' thin-film with an emphasis on growth, critical current properties, and device fabrication.

NanoSQUID magnetometry of individual cobalt nanoparticles grown by focused electron beam induced deposition

We demonstrate the operation of low-noise nano superconducting quantum interference devices (SQUIDs) based on the high critical field and high critical temperature superconductor YBa2Cu3O7 (YBCO) as ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have been patterned by focused ion beam milling. This allows us to precisely define the lateral dimensions of the SQUIDs so as to achieve large magnetic coupling between the nanoloop and individual MNPs. By means of focused electron beam induced deposition, cobalt MNPs with a typical size of several tens of nm have been grown directly on the surface of the sensors with nanometric spatial resolution. Remarkably, the nanoSQUIDs are operative over extremely broad ranges of applied magnetic field (–1 T 1 T) and temperature (0.3 K 80 K). All these features together have allowed us to perform magnetization measurements under different ambient conditions and to detect the magnetization reversal of individual Co MNPs with magnetic moments (1–30) . Depending on the dimensions and shape of the particles we have distinguished between two different magnetic states yielding different reversal mechanisms. The magnetization reversal is thermally activated over an energy barrier, which has been quantified for the (quasi) single-domain particles. Our measurements serve to show not only the high sensitivity achievable with YBCO nanoSQUIDs, but also demonstrate that these sensors are exceptional magnetometers for the investigation of the properties of individual nanomagnets.

Evidence for the movement of macro-vortices on high critical temperature superconductors

In this work, a procedure for inserting currents in rings and their respective vortices was developed. The current circulating around the ring was determined by measuring the magnetic field in its axis. Current and vortices were separated by eliminating the current using a resistor placed in the section through which the whole current circulates. The vortices undergo a Lorentz force traveling over the superconducting net and it dissipate energy. This movement is interrupted by the obstacles found on their way (pinning) and can be seen on the decaying curves especially toward the end of the experiment when the forces get weaker due to the decreasing vortices. This movement of vortices was evidenced by resorting to a long time, during which the vortices have come to a stop. The vortices amount was manipulated by means of the injection of anti-vortices that allowed us to eliminate part of them. This allowed us to observe the decrease in travel speed and the dissipation of energy.

Magnetic properties and pairing tendencies of the iron-based superconducting ladderBaFe2S3: Combinedab initioand density matrix renormalization group study

The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe$_2$S$_3$ [H. Takahashi et al., Nature Materials 14, 1008 (2015)] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi one-dimensional iron-based high critical temperature superconductor. Similarly as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe$_2$S$_3$. The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; (ii) pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, Orbital Selective Mott Phase characteristics develop with doping, with only one Wannier orbital receiving the hole carriers while the other remains half-filled. These results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high critical temperature superconductors.

Superconductor-ferromagnet-superconductor nanojunctions from perovskite materials

The lateral superconductor-ferromagnet–superconductor (SFS) nanojunctions based on high critical temperature superconductor YBa2Cu3Ox (YBCO) and half-metallic ferromagnet La0.67Sr0.33MnO3 (LSMO) thin films were prepared to investigate a possible presence of long range triplet component (LRTC) of Cooper pairs in the LSMO. We applied Ga3+ focused ion beam patterning to create YBCO/LSMO/YBCO lateral type nanojunctions with LSMO length as small as 40nm. The resistivity vs. temperature, critical current density vs. temperature and resistance vs. magnetic field dependence were studied to recognize the LRTC of Cooper pairs in the LSMO. A non-monotonic temperature dependence of junction critical current density and a decrease of the SFS nanojunction resistance in increased magnetic field were observed. Only weak manifestations of LRTC and some qualitative agreement with theory were found out in SFS nanojunctions realized from the perovskite materials. The presence of equal-spin triplet component of Cooper pairs in half-metallic LSMO ferromagnet is not such apparent as in SFS junctions prepared from low temperature superconductors NbTiN and half-metallic ferromagnet CrO2.

Local transport properties of coated conductors by laser-scan imaging methods

Abstract To observe the superconducting current and structural properties of high critical temperature ( T c ) superconductors (HTS), we suggest the following imaging methods: Room temperature imaging (RTI) through thermal heating, low-temperature bolometric microscopy (LTBM) and Raman scattering imaging. RTI and LTBM images visualize thermal-electric voltages as different thermal gradients at room temperature (RT) and superconducting current dissipation at near- T c , respectively. Using RTI, we can obtain structural information about the surface uniformity and positions of impurities. LTBM images show the flux flow in two dimensions as a function of the local critical currents. Raman imaging is transformed from Raman survey spectra in particular areas, and the Raman vibration modes can be combined. Raman imaging can quantify the vibration modes of the areas. Therefore, we demonstrate the spatial transport properties of superconducting materials by combining the results. In addition, this enables visualization of the effect of current flow on the distribution of impurities in a uniform superconducting crystalline material. These imaging methods facilitate direct examination of the local properties of superconducting materials and wires.

Electrical transport anisotropy of uniaxial polycrystalline samples and the effective medium approximation: An application to HTS

In this paper we have applied the effective medium approximation (EMA) to a polycrystalline sample made up of uniaxial crystallites with similar behavior to the high critical temperature superconductors (HTS) at the normal state (σab ≫ σc). As a result the dependence of the anisotropy parameter at the level of the sample, μ=σx/σz, on orientation probability of the grains’ a-axes along a certain preferential direction, γxa is obtained. The intrinsic and shape anisotropy parameters of the crystallites constitute input data. In addition, the dependence of the orientation factor, f, which has been introduced in current models on the transport properties of HTS, is calculated as a function of γxa. These results offer a tool to interpret electrical transport measurements at normal state in granular uniaxial superconducting materials with certain texture degree, by means of the correlation between microstructure and electrical transport properties. Moreover, the comparison between the model and some experimental data suggests the presence of intragranular planar defects in the polycrystalline superconductors. They may affect the measurement of paracoherent resistivity and consequently the determination of f mainly in Bi based samples.

Over-Current Properties of MgB2Wire Cooled by Liquid Hydrogen Under Magnetic Field

Liquid hydrogen (LH 2 ) has excellent properties such as large latent heat, low viscosity, and so on. Because of these properties, LH 2 is expected to be used as a coolant for a high-critical-temperature superconductor (HTS), including MgB 2 . The over-critical-current properties of an HTS are important for the stable designs of HTS devices cooled by LH 2 ; however, the temperature change of a sheathed superconducting wire cannot be revealed only by current-voltage properties beyond critical current, since the current-sharing ratio among MgB 2 and sheath materials is not unknown. In this study, transient over-critical-current tests were performed on a short MgB 2 sample cooled by LH 2 under magnetic field, and the sample temperatures were calculated from test data. In addition, the test sample temperature based on the test was compared with that of the computer simulation result. It was found that the temperature change of the wire just after the transport current exceeds the critical current is affected by external magnetic fields.

A Tale of Two Entangled Instabilities—The Dual Role of δ-O in HgBa2Can-1CunO2(n+1)+δ

Low-energy instabilities in the hole-doped cuprates include, besides short range antiferromagnetic fluctuations and superconductivity, also ubiquitous translational and rotational symmetry breakings. The overwhelming majority of interpretations of these possibly related properties rely on mappings onto three bands spanned by the three atomic orbitals Cu3d(x2−y2)(σ), O2px(σ), and O2py(σ), these three local orbitals spanning the Zhang–Rice band (ZRB), the lower Hubbard bands (LHB) and the upper Hubbard bands (UHB), respectively. Here we demonstrate by means of supercell Density Functional Theory (DFT) (a) how oxygen intercalation affects the structures of the buffer layers, and (b) how the attenuated crystal field pulls two additional oxygen bands in the CuO2 plane to the Fermi level. The self-consistent changes in electronic structure reflected in the corresponding changes in external potential comprise formal properties of the Hohenberg–Kohn theorems. Validation of present days’ approximate exchange-correlation potentials to capture these qualitative effects by means of supercell DFT is made by comparing computed doping dependent structural shifts to corresponding experimentally observed correlations. The simplest generalization of Bardeen–Cooper–Schrieffer (BCS) theory is offered to articulate high-critical temperature superconductivity (HTS) from a normal state where crystal field causes states related to two non-hybridizing bands to coalesce at EF.

Towards a Hybrid High Critical Temperature Superconductor Junction With a Semiconducting InAs Nanowire Barrier

We investigate a new architecture for the implementation of Josephson junctions combining high critical temperature superconductors (HTS) and semiconductor (Sm) nanowires (NWs). The devices are obtained starting from pre-patterned YBaCuO (YBCO) electrodes and assembling suspended InAs-NWs bridges between nearby superconductive banks. Such a non-standard approach is necessary in the case of HTS since growth conditions for cuprates are incompatible with thermal stability of the Sm nanostructures. We investigate the device behavior as a function of the length L of the InAs bridge. For L > 200 nm, all junctions display a tendency to insulation at low temperatures. For L ∼ 200 nm, a metallic-like behavior is obtained, signaling the possible onset of a superconductive transition of the junction. Technological limitations on the width of the gap separating the YBCO banks currently prevent a further scaling. Our results suggest that a further reduction of the size of the trench between the YBCO electrodes can lead to functional YBCO/InAs-NWs/YBCO Josephson junctions.

Fabricating Nanogaps inYBa2Cu3O7−δfor Hybrid Proximity-Based Josephson Junctions

The advances of nanotechnologies applied to high-critical-temperature superconductors (HTSs) have recently given a huge boost to the field, opening new prospectives for their integration in hybrid devices. The feasibility of this research goes through the realization of HTS nanogaps with superconductive properties close to the as-grown bulk material at the nanoscale. Here we present a fabrication approach allowing the realization of YBa2Cu3O7-delta (YBCO) nanogaps with dimensions as small as 35 nm. To assess the quality of the nanogaps, we measure, before and after an ozone treatment, the current-voltage characteristics and the resistance versus temperature of YBCO nanowires with various widths and lengths, fabricated by using different lithographic processes. The analysis of the superconducting transition with a thermally activated vortex-entry model allows us to determine the maximum damage the nanowires undergo during the patterning which relates to the upper bound for the dimension of the nanogap. We find that the effective width of the nanogap is of the order of 100 nm at the superconducting transition temperature while retaining the geometrical value of about 35 nm at lower temperatures. The feasibility of the nanogaps for hybrid Josephson devices is demonstrated by bridging them with thin Au films. We detect a Josephson coupling up to 85 K with an almost ideal magnetic-field response of the Josephson current. These results pave the way for the realization of complex hybrid devices, where tiny HTS nanogaps can be instrumental to study the Josephson effect through barriers such as topological insulators or graphene.

Transport Properties of Melt-Cast-Processed Bi-2212 Bulk Superconductor Bars

Bulk materials of high-critical-temperature superconductors (HTSs) are promising for current leads and fault-current limiters because of negligibly small Joule heating under current transport and very low thermal conductivity. We consider that a Bi-2212 bulk superconductor prepared by the melt-casting process (MCP) is one of the best materials for these applications. In addition, MCP is well known to be a simple and economic process, and also served as a method for obtaining any sizes of HTS bulks consent to requirements for practical applications. In this paper, we present a study on the transport and quench properties of Bi-2212 bulk superconductors doped with $\hbox{K}_{2}\hbox{CO}_{3}$ . First, the MCP samples doped with $\hbox{K}_{2}\hbox{CO}_{3}$ were analyzed by using an X-ray diffractometer and X-ray fluorescence spectrometry. In addition, the critical temperatures of the MCP samples doped with $\hbox{K}_{2}\hbox{CO}_{3}$ were observed. Then, we have investigated the relations between the critical current value and the doping quantity of $\hbox{K}_{2}\hbox{CO}_{3}$ . The value of the direct-current critical current was determined at 77 K, and the self-fields derived from the electric field versus the transport current characteristics were obtained using a criterion of 1 $\mu\hbox{V/cm}$ . Finally, the alternating-current transport properties of the MCP sample were measured, and we have discussed the frequency dependence of the critical current with current distributions

A Full Scale Superconducting Magnetic Levitation (MagLev) Vehicle Operational Line

This paper describes the construction and main components of a full-scale superconducting magnetic levitation vehicle. The prototype, comprising four 1.5-m-long wagons, will travel a short test line of 200 meters, connecting two buildings inside the campus of the Federal University of Rio de Janeiro. The efforts to implement this technology started thirteen years ago with a small-scale prototype in an attempt to prove the concept. The second step was the construction of a functional prototype that could levitate more than one Ton. The actual stage of this project is the construction of an operational prototype mentioned above, designed to transport up to 24 passengers. This work has been reported in several previous editions of the ASC conference. New details about the elevated test line, the permanent magnetic (Nd-Fe-B) guideways, the cryostats with YBCO high critical temperature superconductors, the energy conditioning, the linear induction motor and its regenerative braking, as well as the automatic supply system of liquid nitrogen will be presented in the proposed paper. Tests with this operational prototype demonstrate the technology feasibility.

Comparative study of pure and Co-dopedBaFe2As2

We present a comparative calculation of the electronic structure of the high critical temperature superconductor Co-doped ${\text{BaFe}}_{2}{\text{As}}_{2}$ and its parent compound at the electron correlation level by the embedded cluster method; the electron correlation is calculated through the second-order M\o{}ller-Plesset perturbation theory. The superconducting doped material is represented by the ${\text{Ba}}_{4}{\text{CoFe}}_{4}{\text{As}}_{8}$ cluster. The analysis of the orbital populations in this cluster reveals the formation of an antiferromagnetic order in the Fe plane with a spin-density increase on the central Co atom with respect to the spin density of the central Fe atom of the undoped case. This increase is associated with an increase of the ${d}_{{z}^{2}}$ orbital population of the central atom. However, the formation mechanism of the local magnetic moment implies also a spin transfer from the nearest-neighbor Fe atoms and from the next-nearest-neighbor As atoms to the central Co atom, and it corresponds to a ${J}_{1}\ensuremath{-}{J}_{2}$ antiferromagnetic Heisenberg model. Some particular features of ${d}_{yz}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbitals in the triplet and in the singlet cluster states are interpreted to correspond to a spinless fermion. This result, as well as the result relative to the formation mechanism of the magnetic moments, can be connected with a model of resonating-valence-bond (RVB) superconductors suggested recently by Poilblanc et al. [Phys. Rev. B 89, 241106 (2014)] and based on the Anderson RVB theory.

Modulation effect of interlayer spacing on the superconductivity of electron-doped FeSe-based intercalates.

FeSe-based intercalates are regarded as promising candidates for high-critical temperature (Tc) superconductors. Here we present new Na- and Sr-intercalated FeSe superconductors with embedded linear diamines (H2N)CnH2n(NH2) (abbreviated as DA; n = 0, 2, 3, or 6) prepared using a low-temperature ammonothermal method to investigate the effect of interlayer spacing on the superconductivity of electron-doped FeSes. The embedded DA formed a monolayer or bilayer in the interlayer of FeSe. The interlayer spacing between nearest FeSe layers could be tuned from 0.87 to 1.14 nm without significant change in the Na/Sr content or the ratio of Fe to Se. Importantly, bilayer phases Na/ethylenediamine- and Sr/hydrazine-FeSe show improved structural stability compared to that of Na/NH3-FeSe. The series of Na- and Sr-intercalated FeSe samples exhibited nearly the same high Tc values of 41-46 and 34-38 K, respectively, irrespective of rather different interlayer spacing d. The peculiar insensitivity for both series can be ascribed to the negligible dispersions of bands along the c axis; i.e., Fermi surfaces are nearly two-dimensional when d is larger than a certain threshold value (dsat) of ∼0.9 nm. The Fermi surface shape is already optimal for Tc, and a larger d will not enhance Tc further. On the other hand, the difference in Tc between two series may be explained by the higher carrier doping level in Na/DA-FeSes compared to that in Sr/DA-FeSes, resulting in the increased density of states at the Fermi level and superconducting pairing strength.

Highly Sensitive Magnetic Nanoparticle Imaging Using Cooled-Cu/HTS-Superconductor Pickup Coils

We developed a highly sensitive measurement system of ac magnetic fields for magnetic nanoparticle imaging (MPI). First, we developed a detection system using pickup coils made of cooled Cu Litz-wire and high-critical-temperature superconductor (HTS) tape. The pickup coils were connected to a resonant capacitor in order to enhance the signal voltage generated in the pickup coils. The magnetic field noise at the resonant frequency of about 9 kHz was as low as 13 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and 12 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> for the Cu and HTS coils, respectively. Next, we demonstrated the detection of nanoparticles using the cooled Cu coil and the third harmonic signal generated by the nonlinear magnetization of nanoparticles. An excitation field having a frequency of 3 kHz and root mean square value of 1.6 mT was applied to the magnetic particles, and the third harmonic signal at 9 kHz was detected that reduced the interference from the excitation field. We demonstrated the detection of 100 μg of magnetic nanoparticles. We obtained a clear contour map of the magnetic field from the particles, and could detect the particles located as far as 100 mm under the pickup coil.

YBa2Cu3O7−δ nanorings to probe fluxoid quantization in High Critical Temperature Superconductors

We have realized YBa2Cu3O7−δ (YBCO) nanorings and measured the magnetoresistance R(B) close to the superconducting transition. The large oscillations that we have measured can be interpreted in terms of vortex dynamics triggering the nanowires to the resistive state. The Fast Fourier Transform spectrum of the magnetoresistance oscillations shows a single sharp peak for nanorings with narrower loop arm width: this peak can be univocally associated to a h/2e periodicity as predicted for optimally doped YBCO. Moreover it is a clear evidence of a uniform vorticity of the order parameter inside the rings, confirming a high degree of homogeneity of our nanostructures. This result gives a boost to further investigations of YBCO nanorings at different dopings within the superconducting dome, where in the underdoped regime a R(B) periodicity different from the conventional h/2e has been predicted.

Superconductivity-Induced Transparency in Terahertz Metamaterials

A plasmonic analogue of electromagnetically induced transparency is activated and tuned in the terahertz (THz) range in asymmetric metamaterials fabricated from high critical temperature (Tc) superconductor thin films. The asymmetric design provides a near-field coupling between a superradiant and a subradiant plasmonic mode, which has been widely tuned through superconductivity and monitored by Fourier transform infrared spectroscopy. The sharp transparency window that appears in the extinction spectrum exhibits a relative modulation up to 50% activated by temperature change. The interplay between ohmic and radiative damping, which can be independently tuned and controlled, allows for engineering the electromagnetically induced transparency of the metamaterial far beyond the current state-of-the-art, which relies on standard metals or low-Tc superconductors.