Early Studies of Superconductive Materials and Superconducting Magnet in China(1962～1966)

On the basis of the published literature and the interviews with some participants,this paper introduces the early history of the studies of superconductive materials and superconducting magnet during 1962～ 1966 in China,narrates the achievements of other relevant experimental and theoretical studies of superconductivity in that period briefly,and tries to give the authors' comments on that history.

INFLUENCE OF GEOMETRICAL CONFIGURATION OFSUPERCONDUCTING MATERIAL ON GROWTH OF Nb_3 Sn

Boundary conditions constructed by two typical geometrical configurations related to the manufacturing methods of bronze process and tin-rich Nb tube method have been considered in a diffusion model in which the diffusion of Sn in CuSn matrix plays a major role is as- sumed.The dependence of thickness of Nb_3Sn layer on reaction time has been derived.It is shown that the growth rate of Nb_3Sn relates to the configuration of the superconductor,the geometrical parameters of Nb filaments and CuSn matrix.The theory is qualitatively con- sistent with the experimental results.

Texture Analysis of High T_c.Superconducting YBa_2Cu_3O_(7-x) Ceramic Material

YBaCuO(YBCO) is one of thesuperconducting oxides with transition tem-perature above 90K.It has a orthorhombic crystal structrure ofa layered-perovskite-type with oxygen defi-ciency.This kind of material shows differentdegree of preferred orientation after the

CERAMICS AS CANDIDATE STRUCTURAL MATERIALS FOR CRYOGENIC APPLICATIONS

The use of zirconia-based ceramic materials as smpport materidls for superconducting magnets and in cryopenic engineeriny generally has been considered. The relationship between compsition and mechanical properties at cryogenic temperature has also been investigated.

Elastic, thermodynamic, electronic, and optical properties of recently discovered superconducting transition metal boride NbRuB:An ab-initio investigation

The elastic, thermodynamic, electronic, and optical properties of recently discovered and potentially technologically important transition metal boride NbRuB, are investigated using the density functional formalism. Both generalized gradient approximation （GGA） and local density approximation （LDA） are used for optimizing the geometry and for estimating various elastic moduli and constants. The optical properties of NbRuB are studied for the first time with different photon polarizations. The frequency （energy） dependence of various optical constants complement quite well the essential features of the electronic band structure calculations. Debye temperature of NbRuB is estimated from the thermodynamical study. All these theoretical estimates are compared with published results, where available, and discussed in detail. Both electronic band structure and optical conductivity reveal robust metallic characteristics. The NbRuB possesses significant elastic anisotropy. Electronic features, on the other hand, are almost isotropic in nature. The effects of electronic band structure and Debye temperature on the emergence of superconductivity are also analyzed.

Superconducting Magnetic Flux Transformer at 77K

Superconducting Quantum Interference Device (SQUID) magnetometer is a kind of magnetic flux sensor with high sensitivity, and therefore can be used in geological prospect and biomagnetic field etc.. But the SQUID magnetometer used before has to be used at the temperature of 4.2K provided by liquid helium and thus its application is limited. Since the discovery of high Tc oxide superconductors, scientists have been trying hard to put the SQUID magnetometer into use at 77K. Recently, a new kind of high Tc superconducting magnetic flux transformer winded with one piece of BiPbSrCaCuO superconducting wire is produced. The magnetic flux transformer can be designed to be insensitive to both uniform fields and fields with a constant gradient. In this letter, the fabrication and the properties of the high Tc superconducting magnetic flux transformer is described.

Observation of lateral long range order in superconducting FeTe thin films

We find that the superconductivity in the thin films of the formerly believed non-superconducting parent compound FeTe is accompanied by an emergence of second order with a correlation length of 742 nm and 258 nm at 10 K and 300 K, respectively. The structural phase transition found in iron pnictide superconductors, in non-superconducting FeTe bulk samples, and in FeSe superconducting thin films is not observed in the superconducting FeTe thin films. The interplay between superconductivity and long range order may suggest the crucial role of competition between electronic localization and itinerancy which leads to strong quantum fluctuations in the FeTe system.

Signature of Superconductivity in Pressurized La_(4)Ni_(3)O_(10)

The discovery of high-temperature superconductivity near 80K in bilayer nickelate La_(3)Ni_(2)O_(7)under high pressures has renewed the exploration of superconducting nickelate in bulk materials.The extension of superconductivity in other nickelates in a broader family is also essential.Here,we report the experimental observation of superconducting signature in trilayer nickelate La_(4)Ni_(3)O_(10)under high pressures.By using a modified solgel method and post-annealing treatment under high oxygen pressure,we successfully obtained polycrystalline La_(4)Ni_(3)O_(10)samples with different transport behaviors at ambient pressure.Then we performed high-pressure electrical resistance measurements on these samples in a diamond-anvil-cell apparatus.Surprisingly,the signature of possible superconducting transition with a maximum transition temperature(T_(c))of about 20K under high pressures is observed,as evidenced by a clear drop of resistance and the suppression of resistance drops under magnetic fields.Although the resistance drop is sample-dependent and relatively small,it appears in all of our measured samples.We argue that the observed superconducting signal is most likely to originate from the main phase of La_(4)Ni_(3)O_(10).Our findings will motivate the exploration of superconductivity in a broader family of nickelates and shed light on the understanding of the underlying mechanisms of high-T_(c) superconductivity in nickelates.

HIGH-Tc SUPERCONDUCTIVITY AND PERCOLATION

On microscopic and microstructural levels, the relations between high Tc superconductivity and percolation have been discussed. On the microscopic level, the critical oxygen concentration in YBa2Cu3O7 with Tc around 90 K has been obtained in terms of percolation. On the microstruc(?)ural level, the percolation considerations have provided, usefully theoretical basis for materials design of metal/high-Tc superconducting phase ( nonmetal) composites.

Decoupling of Rattling Mode and Superconductivity in Filled-Skutterudite Ba_(x)Ir_(4)Sb_(12)

The rattling mode,an anharmonic vibrational phonon,is widely recognized as a critical factor in the emergence of superconductivity in caged materials.Here,we present a counterexample in a filled-skutterudite superconductor Ba_(x)Ir_(4)Sb_(12)(x=0.8,0.9,1.0),synthesized via a high-pressure route.Transport measurements down to liquid 3He temperatures reveal a transition temperature(T_(c))of 1.2 K and an upper critical field(H_(c2))of 1.3 T.Unlike other superconductors with caged structures,the Ba_(x)Ir_(4)Sb_(12)(X=P,As,Sb)family exhibits a monotonic decreasing T_(c) with the enhancement of the rattling mode,as indicated by fitting the Bloch–Grüneisen formula.Theoretical analysis suggests that electron doping from Ba transforms the direct bandgap IrSb3 into a metal,with the Fermi surface dominated by the hybridization of Ir 5d and Sb 5p orbitals.Our findings of decoupled rattling modes and superconductivity distinguish the Ba_(x)Ir_(4)Sb_(12) family from other caged superconductors,warranting further exploration into the underlying mechanism.

Clear evidence against superconductivity in hydrides under high pressure

The Meissner effect,magnetic field expulsion,is a hallmark of superconductivity.Associated with it,superconductors exclude applied magnetic fields.Recently,Minkov et al.[Nat.Commun.13,3194(2022)]presented experimental results reportedly showing“definitive evidence of the Meissner effect”in sulfur hydride and lanthanum hydride under high pressure,and Eremets et al.[J.Supercond.Nov.Magn.35,965(2022)]argued that“the arguments against superconductivity(in hydrides)can be either refuted or explained.”Instead,we show here that the evidence presented in those papers does not support the case for superconductivity in these materials.Together with experimental evidence discussed in earlier papers,we argue that this strongly suggests that hydrides under pressure are not high-temperature superconductors.

Effects of Current-Injection on Superconductivity of YBa_2Cu_3O_(7-δ) in La_(0.8)Te_(0.2)MnO_3/YBa_2Cu_3O_(7-δ)Bilayer

La_(0.8)Te_(0.2)MnO_3/YBa_2Cu_3O_(7-δ)(F/S)bilayers were fabricated by electrophoretic technique. The thickness of La_(0.8)Te_(0.2)MnO_3 is ~70 μm, the dimensions of YBa_2Cu_3O_(7-δ) superconductor are 5 mm×10 mm×0.5 mm. The image of cross-sectional profile was measured by scanning electron microscopy (SEM). Standard four-probe method was used for YBa_2Cu_3O_(7-δ) superconducting resistance measurements. Either 1 mA current is injected from S layer to F layer ((+I_(inj))) or from F layer to S layer (-I_(inj)),the normal resistance is lower than that without current injection. The critical transition temperature is higher than that without current injection.

Superconductivity and Structure of BiSrCaEuCuO Compound

Since the discovery of superconductivity of the BiSrCuO system at 20K, the work of synthesizing high Tc superconductors without rare-earths by adding some elements other than rare-earths in the BiSrCuO system has made a lot of progress. Recently, N. Fukushima et al. have synthesized Bi4Sr4RE2Cu4O16+δ (RE = Nd, Eu or Y) by substituting RE for Ca in the Bi4Sr4Ca2Cu4O16+δ superconductor and revealed that it has a crystal structure identical with this superconductor, but it is an insulator. In this paper, the authors report the superconductivity and structure of the BiSrCaEuCuO compound synthesized by adding 5 at% of rare-earth Eu in the BiSrCaCuO system.

Nodeless superconductivity in a quasi-two-dimensional superconductor AuTe2Se(4/3)

We performed ultra-low temperature thermal conductivity measurements on the single crystal of a new gold-based quasi-two-dimensional superconductor Au Te2Se（4/3）, which has a superconducting transition temperature Tc = 2.70 K. A negligible residual linear term κ0/T in zero magnetic field is observed, which suggests fully gapped superconducting state.Furthermore, the field dependence of κ0/T is similar to that of the multi-band s-wave superconductor Ba Fe1.9 Ni0.1 As2 at low field. These results reveal multiple nodeless superconducting gaps in this interesting quasi-two-dimensional superconductor with Berezinsky–Kosterlitz–Thouless topological transition.

High-throughput research on superconductivity

As an essential component of the Materials Genome Initiative aiming to shorten the period of materials research and development, combinatorial synthesis and rapid characterization technologies have been playing a more and more important role in exploring new materials and comprehensively understanding materials properties. In this review, we discuss the advantages of high-throughput experimental techniques in researches on superconductors. The evolution of combinatorial thin-film technology and several high-speed screening devices are briefly introduced. We emphasize the necessity to develop new high-throughput research modes such as a combination of high-throughput techniques and conventional methods.

Effect of Pb Content on Phase Composition and Property of Bi-Pb-Sr-Ca-Cu-O System Superconductors

The addition of Pb in the superconductors of BiSrCaCuO system is very helpful for growth of the high-Tc phase (Tc 110K). We prepared a series of samples with nominal composition of Bi2-xPbxSr2Ca2Cu3Oy (0.1&lex&le2). The zero resistance transition temperature Tc of 106K and the critical transport current density Jc of 1 × 103A/cm2 at 77K have been obtained for the samples of Bi2-xPbxSr2Ca2Cu3Oy (x=0.2 and 0.3). The X-ray diffraction analysis and measurement of AC magnetic susceptibility confirmed that the material is comprised of single high-Tc phase. We also report the magnetic properties of this material as well as the results of TEM observation.

An Extended Model for Coexistence of Superconductivity and Paramagnetism in High-T_c Superconductors

In the present work, the total magnetization in superconducting state is separated into critical state and paramagnetic components in terms of an H（x）-dependent magnetic flux density. Utilizing this model, we reproduce successfully M-H curves measured by Sandu et al. [Phys. Rev. B 74 （2006） 184511] and Sandu et al. [J. Supercond. Incorp. Novel Magn. 17 （2004） 701] for different forms of Jc.

A short review of the recent progresses in the study of the cuprate superconductivity

The last 15 years have witnessed important progresses in our understanding of the mechanism of superconductivity in the high-Tc cuprates.There is now strong evidence that the strange metal behavior is induced by the quantum critical fluctuation at the pseudogap end point,where the Fermi surface changes its topology from hole-like to electron-like.However,experiments show that the quantum critical behavior in the high-Tc cuprates is qualitatively different from that observed in the heavy Fermion systems and the iron-based superconductors,in both of which the quantum critical behavior can be attributed to the quantum phase transition toward a symmetry breaking phase.The fact that the pseudogap exists as a spectral gap without a corresponding symmetry breaking order,together with the fact that the strange metal behavior occurs as a quantum critical behavior without a corresponding symmetry breaking phase transition,exposes the central difficulty of the field:the lack of a universal low energy effective theory description of the high-Tc phenomenology beyond the Landau paradigm.Recent experiments imply that the dualism between the local moment and the itinerant quasiparticle character of the electron in the high-Tc cuprates may serve as an organizing principle to go beyond the Landau paradigm and may hold the key to the mystery of the pseudogap phenomena and the strange metal behavior.It is the purpose of this review to provide an introduction to these recent progresses in the study of the high-Tc cuprate superconductors and their implications on the construction of a coherent picture for the high-Tc problem.

Heat Treatment of Nd_(1+x)Ba_(2-x)Cu_3O_(7-δ) Superconductors

Two kinds of Nd 1+ x Ba 2- x Cu 3O 7- δ , the sintered samples and zone melted samples, were treated in pure Ar at 950 ℃. The substitution of Nd ions for Ba ions in the Nd 1+ x Ba 2- x Cu 3O 7- δ before and after the heat treatment was investigated by XRD. In order to know the effects of heat treatment, the T c and J c of samples with and without the heat treatment in Ar were comparatively studied. The results show that the substitution of Nd for Ba decreases, whereas T c and J c increase after the treatment. The Nd 1+ x Ba 2- x Cu 3O 7- δ samples were oxygenated in pure oxygen at 300 ℃ . Based on the XRD spectra it was found that the samples with x <0.4 can transform from tetragonal phase into orthorhombic phase after the oxygenation, whereas in the sample with x >0.4 no phase transition occurs even after a long time oxygenation.

Recent advances in quasi-2D superconductors via organic molecule intercalation

Superconductivity at the 2D limit shows emergent novel quantum phenomena, including anomalously enhanced H_(c2),quantum metallic states and quantum Griffiths singularity, which has attracted much attention in the field of condensed matter physics. In this article, we focus on new advances in quasi-2D superconductors in the bulk phase using an organic molecular electrochemical intercalation method. The enhanced superconductivity and emergent pseudogap behavior in these quasi-2D superconductors are summarized with a further prospect.