Much of what we know about the electronic states of high-temperature superconductors is due to photoemission and scanning tunneling spectroscopy studies of the compound Bi2212. The demonstration of well-defined quasiparticles in the superconducting state has encouraged many theorists to apply the conventional theory of metals, Fermi-liquid theory, to the cuprates. In particular, the spin excitations observed by neutron scattering at energies below twice the superconducting gap energy are commonly believed to correspond to an excitonic state involving itinerant electrons. Here, we present the first measurements of the magnetic spectral weight of optimally-doped Bi2212 in absolute units. The lack of temperature dependence of the local spin susceptibility across the superconducting transition temperature, T_c, is incompatible with the itinerant calculations. Alternatively, the magnetic excitations could be due to local moments, as the magnetic spectrum is similar to that in LBCO where quasiparticles and local moments coexist.
A facility capable of testing superconducting cables with current of tens of kA is essential for the development of large superconducting magnets. A superconducting transformer (SCT) is a suitable choice as a high DC current source for testing superconducting cables. In this work, we will present our experimental results of a SCT up to output current of 45 kA. The properties of this SCT is characterized at 4.2 K. Its behaviors during quenches at different current levels are studied.
Charge order is commonly believed to compete with superconducting order. An intertwined form of superconducting wave function, known as pair-density-wave (PDW) order, has been proposed; however, there has been no direct evidence, theoretical or experimental, that it forms the ground state of any cuprate superconductor. As a test case, we consider \lbco\ with $x=1/8$, where charge and spin stripe orders within the CuO$_2$ planes compete with three-dimensional superconducting order. We report measurements of the superconducting critical current perpendicular to the planes in the presence of an i…
$3d_{z^2}$ orbital delocalization and magnetic collapse in superconducting (La,Pr)$_3$Ni$_2$O$_{7-δ}$ films
Diamond Light Source（钻石光源）；National Synchrotron Radiation Laboratory and School of Nuclear Science and Technology, University of Science and Technology of China（中国科学技术大学核科学与技术学院和同步辐射实验室）；Southern University of Science and Technology（南方科技大学）；Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所和北京凝聚态物理国家研究中心）；University of Chinese Academy of Sciences（中国科学院大学）；Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area（粤港澳大湾区量子科学中心）
A simple tabletop setup based on a superconducting quantum interference device is proposed for testing the gravitational interaction. A D-shaped superconducting loop has the straight segment immersed inside a massive sphere while the half-circle segment is wrapped around the sphere. The superconducting condensate within the straight arm of the loop thus bathes inside a gravitational simple harmonic oscillator potential while the condensate in the half-circle arm bathes in the constant gravitational potential around the sphere. The resulting phase difference at the Josephson junctions on both s…
We present a phenomenological calculation of the quasiparticle-interference (QPI) pattern and inelastic Neutron scattering (INS) spectra in iron-pnictide and layered iron-selenide compounds by using materials specific band-structure and superconducting (SC) gap properties. As both the QPI and the INS spectra arise due to scattering of the Bogolyubov quasiaprticles, they exibit an one-to-one correspondence of the scattering vectors and the energy scales. We show that these two spectroscopies complement each other in such a way that a comparative study allows one to extract the quantitative and …
Superconducting single flux quantum (SFQ) circuits can process information at extremely high speeds, in the range of hundreds of GHz. SFQ circuits are based on Josephson junction cells for switching logic and ballistic transmission for transferring SFQ pulses. Multi-chip modules (MCM) are often used to implement larger complex designs, which cannot be fit onto a single chip. We have optimized the design of wideband interconnects for transferring signals and SFQ pulses between chips in flip-chip MCMs and evaluated the importance of several design parameters such as the geometry of bump pads on …
Over the past several decades, a rich series of experiments has repeatedly verified the quantum nature of superconducting devices, leading some of these systems to be regarded as artificial atoms. In addition to their application in quantum information processing, these `atoms' provide a test bed for studying quantum mechanics in macroscopic limits. Regarding the last point, we present here a feasible protocol for directly testing time reversal symmetry through the verification of the microreversibility principle in a superconducting artificial atom. Time reversal symmetry is a fundamental pro…
Terahertz imaging system with on-chip superconducting Josephson plasma emitters for nondestructive testing
National Institute of Advanced Industrial Science and Technology (AIST)（产业技术综合研究所）；James Watt School of Engineering, University of Glasgow（格拉斯哥大学詹姆斯·瓦特工程学院）；Faculty of Pure and Applied Sciences, University of Tsukuba（筑波大学理工学群）
Bending-like stress induced by solder joint under uniaxial tensile testing in 2G-HTS tapes: Impact and optimization approach
School of Electrical Engineering, Shanghai Jiao Tong University（上海交通大学电气工程学院）；State key Laboratory of High-Efficiency special cable technology, Shanghai Jiao Tong University（上海交通大学高效特种电缆技术国家重点实验室）；Key Laboratory of Applied Superconductivity, Institute of Electrical Engineering, Chinese Academy of Sciences（中国科学院电气工程技术研究所超导应用重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）
Superconductivity in the iron pnictides and chalcogenides is closely connected to a bad-metal normal state and a nearby antiferromagnetic order. Therefore, considerable attention has been focused on the role of electron correlations and spin dynamics. In this article, we summarize some key experiments that quite directly imply strong electron correlations in these materials, and discuss aspects of the recent theoretical studies on these issues. In particular, we outline a $w$-expansion, which treats the correlation effects using the Mott transition as the reference point. For the parent system…
We present a practical design and implementation of a broadband sample holder suitable for microwave experiments with superconducting integrated circuits at millikelvin temperatures. Proposed design can be easily integrated in standard dilution cryostats, has flat pass band response in a frequency range from 0 to 32 GHz, allowing the RF testing of the samples with substrate size up to 4x4 mm. The parasitic higher modes interference in the holder structure is analyzed and prevented via design considerations. The developed setup can be used for characterization of superconducting parametric ampl…
Large high field superconducting magnets often requires high current superconducting cables. In order to develop these cables, a facility capable of providing high magnetic field with large sampling area as well as electrical current of tens of kA is essential. A superconducting transformer is an energy-efficient and low-cost way to provide large current to superconducting cables. Previously, we co-developed a superconducting transformer and successfully tested it to a maximum output current of 45 kA in zero magnetic field. In this work, this superconducting transformer is installed to the 12 …
The Continuous Spontaneous Localization (CSL) model is an alternative formulation of quantum mechanics which introduces a noise coupled non linearly to the wave function to account for its collapse. We consider CSL effects on quantum computers made of superconducting transmon qubits. As a direct effect CSL reduces quantum superpositions of the computational basis states of the qubits: we show the reduction rate to be negligibly small. However, an indirect effect of CSL, dissipation induced by the noise, also leads transmon qubits to decohere, by generating additional quasiparticles. Since the …
In superconducting circuits with interbit untunable (e.g., capacitive) couplings, ideal local quantum operations cannot be exactly performed on individual Josephson qubits. Here we propose an effective dynamical decoupling approach to overcome the "fixed-interaction" difficulty for effectively implementing elemental logical gates for quantum computation. The proposed single-qubit operations and local measurements should allow testing Bell's inequality with a pair of capacitively-coupled Josephson qubits. This provides a powerful approach, besides spectral-analysis [Nature \textbf{421}, 823 (20…
A dirty BCS superconductor with magnetic impurities is studied. Asymptotic solution of the thermodynamics of such superconductor with spin $1/2$ and $7/2$ magnetic impurities, is found. To this end, the system's free energy $f(H, β)$ is bounded from above and below by mean-field type bounds, which are shown to coalesce almost exactly in the thermodynamic limit, provided the impurity concentration is sufficiently small. The resulting mean-field equations for the gap $Δ$ and a parameter $ν$, characterizing the impurity subsystem, are solved and the solution minimizing $f$ is found for various va…
The (Ca_xLa_(1-x))(Ba_(1.75-x)La_(0.25+x))Cu_(3)O_(y) system is ideal for testing theories of high temperature superconductivity, since nearly the full range of doping is controlled by y, and T_(c)^max is continuously controlled by x, with minimal structural changes. We investigate this system with both transverse and longitudinal field MuSR. This allows us to re-examine the Uemura relation, the nature of the spontaneous magnetic fields below T_(c), and the relation between their appearance temperature T_(g) and T_(c)^max . Our major findings are: (I) the Uemura relation is respected by CLBLCO…
Since the discovery of the unconventional copper-oxide high-transition-temperature superconductors (HTS), researchers have explored many methods to fabricate superconducting tunnel junctions from these materials for both superconducting electronics operating at the practical temperature of liquid nitrogen (77 K) and for fundamental measurements essential for testing and guiding theories of these remarkable superconductors. The difficulty is that the traditional estimate of the superconducting coherence length is very short and anisotropic in these materials, typically ~2 nm in the a-b plane an…
The field of electron spin resonance is in constant need to improve its capabilities. Among other things, this means having better resonators which would provide improved spin sensitivity, as well as enable larger microwave magnetic field power conversion factors. Surface micro resonators, made of small metallic patches on a dielectric substrate, provide very good absolute spin sensitivity and high conversion factors due to their very small mode volume. However, such resonators suffer from having a relatively low quality factor, which offsets some of their significant potential advantages. The…
The search for new superconducting materials approaching room temperature benefits from having a variety of testing methodologies to confirm and characterize the presence of superconductivity. Often the first signatures of new superconducting species occur incompletely and in very small volume fractions. These trace amounts may be too weak to produce an observable Meissner effect and the resistance may not go completely to zero if the percolation threshold is not met. Under these conditions, secondary behavior--such as transitions or cross overs in the temperature dependence of magnetoresistan…
Experimental studies of the electronic structure remain the basic means for understanding the nature of high-temperature superconductivity (HTSC) and testing relevant theoretical models. Appreciable contributions to establish the overall picture in HTSC have recently been made by investigations on the charge dynamics in BSCCO (ref. 1) and the spin dynamics in YBCO, using Angle Resolved Photoemission Spectroscopy (ARPES) and Inelastic Neutron Scattering (INS), respectively. Concentration of each of these techniques on a "suitable" compound turns out to be a barrier on the way to a crucial quant…
