EXPERIMENTAL EVIDENCE OF FLUX JUMPS IN Y-Ba-Cu-O SUPERCONDUCTORS

The time dependence of the penetration of a weak ac field into Y-Ba-Cu-O superconductors at various dc fields,0-1500G,was measured at liquid nitrogen temperature.It is found that the signals are very unstable at certain field regions for some of the samples.We believe that this is a direct evidence of the existence of flux jumps which are characteristic of granular superconductors.

A TENTATIVE MODEL FOR HIGH Tc Y-Ba-Cu-O SUPERCONDUCTORS FROM HREM STUDIES

A high Tc Y-Ba-Cu-O superconductor was prepared with a zero-resistance temperature at 89.9K.High resolution electron microscopy(HREM)indicates that the structure of this material is multiphase and looks like some insulating islands surrounded by regions of conductive phase.There exist many defects in the conductive phase which will be transformed into non-crystalline state after prolonged electron bombardment.

Ge Film Contacts to Radio Frequency Sputtered Y-Ba-Cu-O Superconductor Film

The semiconductor-superconductor con tact system of Ge/Y-Ba-Cu-O(YBCO)/SrTiO_(3) has been successfully fabricated by two steps of deposition.The YBCO film in the contact of Ge/YBCO did not lose its superconductivity and its T_(c)(on set)did not degrade as well.The top layer of Ge was polycrystalline with preferred orientation corresponding to the epitaxial structure of the underlayer of YBCO.

FAR IR SPECTRA OF Y-Ba-Cu-O SUPERCONDUCTOR SYSTEM

High Tc superconductivity has recently been discoveredt. The results obtained in our laboratory and reported here confirm high-temperature superconductivity in Y-Ba-Cu-O system and further present some preliminary results of far infrared absorption spectra of YBa2Cu3Ox and YBaCu2Ox at room temperature and liquid ni-

Evolution of Superconducting-Transition Temperature with Superfluid Density and Conductivity in Pressurized Cuprate Superconductors

What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law known as Homes'law,there is a growing consensus in the community that the Tc value of the cuprate superconductors is closely linked to the superfluid density(ρ_(s))of its ground state and the conductivity(σ)of its normal state.However,all the data supporting this empirical law(ρ_(s)=AσT_(c))have been obtained from the ambientpressure superconductors.In this study,we present the first high-pressure results about the connection of the quantities of ρ_(s) and σ with T_(c),through the studies on the Bi_(1.74)Pb_(0.38)Sr_(1.88)CuO_(6+δ)and Bi_(2)Sr_(2)CaCu_(2)O_(8+δ),in which the value of their high-pressure resistivity(ρ=1/σ)is achieved by adopting our newly established method,while the quantity ofρs is extracted using Homes'law.We highlight that the Tc values are strongly linked to the joint response factors of magnetic field and electric field,i.e.,ρ_(s) and σ,respectively,implying that the physics determining T_(c) is governed by the intrinsic electromagnetic fields of the system.

POINT-CONTACT TUNNELING INVESTIGATION OF THE SUPERCONDUCTORS IN Y-Ba-Cu-O SYSTEM

Point-contact tunneling measurements of the oxide superconductor Y-Ba-Cu-O were carried out with both Nb and Mo tips.An energy gap,Δ=18.5meV and 2Δ/kT_(c)=4.7 were obtained.The result is consistent with the strong-coupling theory.The tunneling conductance curves indicate a granular feature of the sample.

Strong Anisotropic Order Parameters at All-Nitride Ferromagnet/Superconductor Interfaces

Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Cooper pairs and ferromagnetic exchange interactions.The proximity effects between transition metal nitrides(TMNs)are scarcely investigated due to the formidable challenges of fabricating high-quality SC/FM interfaces.We fabricated heterostructures comprising SC titanium nitride(TiN)and FM iron nitride(Fe_(3)N)with precise chemical compositions and atomically well-defined interfaces.The magnetoresistance of Fe_(3)N/TiN heterostructures shows a distinct magnetic anisotropy and strongly depends on the external perturbations.Moreover,the superconducting transition temperatureT_(C) and critical field of TiN experience notable suppression when proximity to Fe_(3)N.We observe the intriguing competition of interfacial spin orientations near𝑇T_(C)(∼1.25 K).These findings not only add a new materials system for investigating the interplay between superconductor and ferromagnets,but also potentially provide a building block for future research endeavors and applications in the realms of superconducting spintronic devices.

Controversy Clouds Real Progress in Superconductor Research

In the 8 March 2023 issue of the journal Nature,a paper attracted global attention with the report of a new superconductor material exhibiting ground-breaking properties[1,2].A group led by Ranga P.Dias,assistant professor of mechanical engineering at the University of Rochester(Rochester,NY,USA),described a hydride material that superconducted at around room temperature,albeit at pressures 10000 times greater than atmospheric pressure[3].

Design of high-temperature superconductors at moderate pressures by alloying AlH3 or GaH3

Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achieve this.We focus on a series of alloyed hydrides with the AMH_(6)composition,which can be made via alloying A15 AH_(3)(A=Al or Ga)with M(M=a group IIIB or IVB metal),and study their behavior under pressure.Seven of them are predicted to maintain the A15-type structure,similar to AH_(3)under pressure,providing a platform for studying the effects of alloying on the stability and superconductivity of AH_(3).Among these,the A15-type phases of AlZrH_(6)and AlHfH_(6)are found to be thermodynamically stable in the pressure ranges of 40–150 and 30–181 GPa,respectively.Furthermore,they remain dynamically stable at even lower pressures,as low as 13 GPa for AlZrH_(6)and 6 GPa for AlHfH_(6).These pressures are significantly lower than that required for stabilizing A15 AlH3.Additionally,the introduction of Zr or Hf increases the electronic density of states at the Fermi level compared with AlH3.This enhancement leads to higher critical temperatures(Tc)of 75 and 76 K for AlZrH_(6)and AlHfH_(6)at 20 and 10 GPa,respectively.In the case of GaMH_(6)alloys,where M represents Sc,Ti,Zr,or Hf,these metals reinforce the stability of the A15-type structure and reduce the lowest thermodynamically stable pressure for GaH_(3) from 160 GPa to 116,95,80,and 85 GPa,respectively.Particularly noteworthy are the A15-type GaMH_(6)alloys,which remain dynamically stable at low pressures of 97,28,5,and 6 GPa,simultaneously exhibiting high Tc of 88,39,70,and 49 K at 100,35,10,and 10 GPa,respectively.Overall,these findings enrich the family of A15-type superconductors and provide insights for the future exploration of high-temperature hydride superconductors that can be stabilized at lower pressures.

Prediction of novel layered indium halide superconductors

We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV,respectively.By substituting O with F,both of them become metallic and superconducting at low temperature.The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity.The total electron-phonon coupling strength are 1.86 and 1.48,while the superconducting transition temperature(T_(c))are about 7.2 K and 6.5 K with 10%and 5%F doping for LaOInF_(2)and LaOInCl_(2),respectively.

Two-fold symmetry of the in-plane resistance in kagome superconductor Cs(V_(1-x)Ta_(x))_(3)Sb_(5) with enhanced superconductivity

The kagome superconductor CsV_(3)Sb_(5) has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave(CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electronic orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V_(1-x)Ta_(x))_(3)Sb_(5) by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of x is over 0.07. Concurrently, the superconductivity is enhanced monotonically from T_(c) ~ 2.8 K at x = 0 to 5.2 K at x = 0.12. Intriguingly, in the absence of CDW, Cs(V_(1-x)Ta_(x))_(3)Sb_(5)(x = 0.12) crystals exhibit a pronounced two-fold symmetry of the in-plane angular-dependent magnetoresistance(AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V_(1-x)Ta_(x))_(3)Sb_(5). Our findings demonstrate that Cs(V_(1-x)Ta_(x))_(3)Sb_(5) with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.

Topological superconductors with spin-triplet pairings and Majorana Fermi arcs

We construct a three-dimensional topological superconductor Bogoliubov–de Gennes(BdG)Hamiltonian with the normal state being a three-dimensional topological insulator.By introducing inter-orbital spin-triplet pairings term△3,there are topological Majorana nodes in the bulk and they are connected by Majorana Fermi arcs on the surface,similar to the case of Weyl semimetal.Furthermore,by adding an inversion-breaking term to the normal state,momentum-independent pairing terms with different parities can coexist in the Bd G Hamiltonian,which creates more Majorana modes similar to Andreev bound states and a richer phase diagram.

The Influence of Electron Transfer on Tc in Superconductors

Increase of Tc in Al1−x(SiO2)x cermets with increasing x is caused by electron transfer from the Al grains to the SiO2 phase occupying surface states, expressed by Tc/Tc,max=1−γ⋅n2(*), where n is the electron density in the Al phase and γa characteristic parameter. Decrease of Tc in Pb-Cu-sandwiches is attributed to the electron transfer from the Cu film to the Pb film. γand Tc,maxin equation (*) stands for the influence of the electron-phonon interaction and n2for the influence of the electron-electron Coulomb repulsion on Tc. The result that equation (*) holds for both hole-doped cuprate high-temperature superconductivity (HTSC) and Al1−x(SiO2)x cermets is an important indication that common mechanisms underlie HTSC and classical superconductors. The difference between the two is that in HTSC, electron transfer occurs between different electronic bands, but in Al1−x(SiO2)x cermets between different phases.

Effect of the mixing of s-wave and chiral p-wave pairings on electrical shot noise properties of normal metal/superconductor tunnel junctions

We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.

High Harmonic Spectroscopy Retrieves Electronic Structure of High-pressure Superconductors

High pressure has revealed surprising physics and creates novel states in condensed matter.Exciting examples include near-roomtemperature superconductivity(T_(c)>200 K)in highlypressured hydrides such as H_(3)S and LaH_(10).

Electronic Structure Investigation of 12442 Iron-Based Superconductors Based on Block-Layer Model

Superconducting transition temperature(Tc),as a crucial parameter,exploring its relationship with various macroscopic and microscopic factors helps to understand the mechanism of high-temperature superconductivity from multiple perspectives,aiding in a multidimensional comprehension of high-temperature superconductivity mechanisms.Drawing inspiration from the block-layer structure models of cuprate superconductors,we computationally investigated the interlayer interaction energies in the 12442-type iron-based superconducting materials AkCa_(2)Fe_(4)As_(4)F_(2)(Ak=K,Rb,Cs)systems based on the block-layer model and explored their relationship with Tc.We observed that an increase in interlayer combinative energy leads to a decrease in Tc,while conversely,a decrease in interlayer combination energy results in an increase in Tc.Further,we found that the contribution of the Fe 3d band structure,especially the 3dz2 orbital,to charge transfer is significant.

高T_cY-Ba-Cu-O超导体临界电流密度的研究(英文)

0 Introduction In recent years, the study of Y-Ba-Cu-O superconductor have made much progress. The superconducting applications are showing bright future. Generally, critical current is very lower (especially bulk sample ). The Largest J_c is only 10~3 A/cm^2. Ordinarilly, the typical critical current of Nb-Ti alloy is 10~6 A/cm^2 about 4.2 K. Hence, the level of current density have become a problem interested in by scientists. In this paper, microstrueture of Y_1 Ba_2 Cu_2 O_(7-8) superconductor is examined. The grade intersection-tunnel modal is put forward here. Some mecha-

Y-Ba-Cu-O超导体中氟代氧的研究

以CuF_2为配方试剂之一,用一步合成法制备Y-Ba-cU--(O,F)超导体,其一些主要性能都比不合氟的Y-Ba-Cu-O超导体有一定程度的提高。X-射线,红外及顺磁共振谱等显示,F^-离子进入了123相晶格。文中还讨论了氟对超导电性的作用。

掺氟对Y-Ba-Cu-O高温超导体电子结构的影响

采用Recursion方法计算了不同掺氟量和不同替代位置下Y-Ba-Cu-O的电子结构,从掺氟Y-Ba-Cu-O各晶位的态密度(DOS),可进一步得到Fermi能EF、Fermi能级处的态密度N(EF)以及各晶位原子价等重要数据.各模型的计算结果表明,掺入氟后引起CuO2平面上Cu的原子价升高和O的价位变得更负,使Cu位空穴数目增加和O位空穴数目减少,且以后者的变化为主.掺氟改变了Y-Ba-Cu-O中CuO2平面上载流子的浓度,影响了电荷从CuO2平面向CuO链的转移,增加了Fermi面电子浓度,这可能是对高温氧化物超导电性产生影响的原因.

Y-Ba-Cu-O超导材料的热分析研究

本文制备了T_c=95K的Y-Ba-Cu-O超导体。用热分析方法研究了Y-Ba-Cu-O超导体固相反应的烧结温度。并就烧结温度对超导体性能的影响机制进行了探讨。