Suchergebnisse

We examine coherent phonons in a strongly driven sample of optimally-doped high temperature superconductor YBa2Cu3O7−δ . We observe a nonlinear lattice response of the 4.5 THz copper-oxygen vibrational mode at high excitation densities, evidenced by the observation of the phonon third harmonic and indicating the mode is strongly anharmonic. In addition, we observe how high-amplitude phonon vibrations modify the position of the electronic charge transfer resonance. Both of these results have important implications for possible phonon-driven nonequilibrium superconductivity ; This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreement No. 758461 and was supported by Spanish MINECO (Severo Ochoa Grants No. SEV-2015-0522 and No. SEV-2015-0496), Ramón y Cajal programme RYC2013-14838, and Fondo Europeo de Desarrollo Regional FIS2015-67898-P (MINECO/FEDER), MAT2014-51778- C2-1-R as well as Fundació Privada Cellex, and CERCA Programme/Generalitat de Catalunya. ; Peer reviewed

After half a century of debate, superconductivity in doped SrTiO3 has come to the fore again with the discovery of interfacial superconductivity in the LaAlO3 /SrTiO3 heterostructures. While these interfaces share the interesting properties of bulk SrTiO3, quantum confinement generates a complex band structure involving bands with different orbital symmetries whose occupancy is tunable by electrostating doping. Multigap superconductivity has been predicted to emerge in LaAlO3 /SrTiO3 at large doping, with a Bose-Einstein condensation character at the Lifshtiz transition. In this article, we report on the measurement of the upper critical magnetic field Hc2 of superconducting (110)-oriented LaAlO3 /SrTiO3 heterostructures and evidence a two-gap superconducting regime at high doping. Our results are quantitatively explained by a theoretical model based on the formation of an unconventional s±-wave superconducting state with a repulsive coupling between the two condensates. ; This work was supported by the ANR PRC (QUANTOP), by the QuantERA ERA-NET Cofund in Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Program (QUANTOX) and the Île de France SESAME program, by the PID2020-118479RB-I00, PID2020-112548RB-100 and Severo Ochoa FUNFUTURE (CEX2019-000917-S) projects of the Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033), by the Generalitat de Catalunya (2017 SGR 1377), by Sapienza Università di Roma, through the projects, Ateneo 2018 (Grant No. RM11816431DBA5AF), Ateneo 2019 (Grant No. RM11916B56802AFE), Ateneo 2020 (Grant No. RM120172A8CC7CC7), and by the Italian Ministero dell'Istruzione, dell'Università e della Ricerca, through the Project No. PRIN 2017Z8TS5B. G.S. acknowledges financial support from the Beatriu de Pinós Programme and the Ministry of Research and Universities of the Government of Catalonia, with research Grant No. 2019 BP 00207. ; With funding from the Spanish government through the 'Severo Ochoa Centre of ...

I The Superconducting State of Materials and Methods of Estimating It -- The Phenomenon of Superconductivity -- Empirical Rules -- Methods of Measuring the Critical Superconducting Characteristics of Metals and Alloys -- Low-Temperature Technique -- Metallography of Superconducting Alloys -- Literature Cited -- II Superconducting Elements -- Properties of Superconducting Elements -- Effect of Deformation and Interstitial Impurities on the Superconducting Properties of the Elements -- Literature Cited -- III Superconducting Compounds -- Compounds with the Cr3Si Structure -- Interstitial Phases and Certain Other Compounds of Metals with Nonmetals -- Sigma and Laves Phases and Similar Compounds -- Superconducting Compounds with Other Types of Structures -- Effect of Alloying Elements and Impurities on the Structure and Properties of Compounds -- Effect of Heat Treatment and Other Factors on the Superconducting Characteristics of Compounds -- Literature Cited -- IV Physicochemical Analysis of Superconducting Systems -- Binary Superconducting Systems -- Ternary and More Complex Superconducting Systems -- Literature Cited -- V Production of Superconducting Materials -- Effect of Composition, Deformation, and Heat Treatment on the Critical Current of Superconducting Alloys -- Technology of the Production of Superconducting Alloys -- Properties and Production Technology of Parts Made from Superconducting Compounds -- Literature Cited -- VI Applications -- Superconducting Magnets -- Computing Technology -- Electronics and Measuring Technology -- Nuclear Power and Space -- Electrical Machines -- Conclusion -- Literature Cited.

Abstract
Electronic anisotropy ("nematicity") has been detected in cuprate superconductors by various experimental techniques. Using angle-resolved transverse resistance (ARTR) measurements, a very sensitive and background-free technique that can detect 0.5% anisotropy in transport, we have observed it also in La2-xSrxCuO4 (LSCO) for 0.02 ≤ x ≤ 0.25. A central enigma in LSCO is the rotation of the nematic director (orientation of the largest longitudinal resistance) with temperature; this has not been seen before in any material. Here, we address this puzzle by measuring the angle-resolved transverse magnetoresistance (ARTMR) in LSCO. We report the discovery of colossal transverse magnetoresistance (CTMR)—an order-of-magnitude drop in the transverse resistivity in the magnetic field of 6 T. We show that the apparent rotation of the nematic director is caused by anisotropic superconducting fluctuations, which are not aligned with the normal electron fluid, consistent with coexisting bond-aligned and diagonal nematic orders. We quantify this by modeling the (magneto-)conductivity as a sum of normal (Drude) and paraconducting (Aslamazov–Larkin) channels but extended to contain anisotropic Drude and Cooper-pair effective mass tensors. Strikingly, the anisotropy of Cooper-pair stiffness is much larger than that of the normal electrons. It grows dramatically on the underdoped side, where the fluctuations become quasi-one-dimensional. Our analysis is general rather than model dependent. Still, we discuss some candidate microscopic models, including coupled strongly-correlated ladders where the transverse (interladder) phase stiffness is low compared with the longitudinal intraladder stiffness, as well as the anisotropic superconducting fluctuations expected close to the transition to a pair-density wave state.

Modulation of carrier concentration in strongly correlated oxides offers the unique opportunity to induce different phases in the same material, which dramatically change their physical properties, providing novel concepts in oxide electronic devices with engineered functionalities. This work reports on the electric manipulation of the superconducting to insulator phase transition in YBa2Cu3O7−δ thin films by electrochemical oxygen doping. Both normal state resistance and the superconducting critical temperature can be reversibly manipulated in confined active volumes of the film by gate-tunable oxygen diffusion. Vertical and lateral oxygen mobility may be finely modulated, at the micro- and nano-scale, by tuning the applied bias voltage and operating temperature thus providing the basis for the design of homogeneous and flexible transistor-like devices with loss-less superconducting drain–source channels. We analyze the experimental results in light of a theoretical model, which incorporates thermally activated and electrically driven volume oxygen diffusion. ; We acknowledge the financial support from Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-51778-C2-1-R), co-financed by the European Regional Development Fund. We also thank the support from the European Union for NanoSC Cost Action (MP1201), NANOCOHYBRI (CA 16218) and ERC-2014-ADG-669504, and from the Catalan Government with 2014-SGR-753 and Xarmae. A.F.-R. and J.C.G.-R. thank Spanish Ministry of Economy for his FPI Spanish grants (BES-2016-077310, BES-2012-053814). ; Peer reviewed

We show that the magnetic ordering of coupled atomic dimers on a superconductor is revealed by their intragap spectral features. Chromium atoms on the superconductor β-Bi2Pd surface display Yu-Shiba-Rusinov bound states, detected as pairs of intragap excitations in tunneling spectra. By means of atomic manipulation with a scanning tunneling microscope's tip, we form Cr dimers with different arrangements and find that their intragap features appear either shifted or split with respect to single atoms. These spectral variations are associated with the magnetic coupling, ferromagnetic or antiferromagnetic, of the dimer, as confirmed by density functional theory simulations. The striking qualitative differences between the observed tunneling spectra prove that intragap Shiba states are extremely sensitive to the magnetic ordering on the atomic scale ; We thank Javier Zaldivar and Joeri de Bruijckere for developing the deconvolution process and Sebastian Bergeret for discussions. D.-J. C. and J. I. P. thank the European Union for support under the H2020-MSCA-IF-2014 Marie-Curie Individual Fellowship program (Proposal No. 654469), Spanish MINECO (MAT2016-78293-C6-1-R), Diputacion Foral de Gipuzkoa for Grant No. 64/15, and the European Regional Development Fund (ERDF). N. L. thanks Spanish MINECO (Grant No. MAT2015-66888-C3-2-R). M. M. U. acknowledges Spanish MINECO (MAT2014-60996-R). E. H., I. G., and H. S. acknowledge FIS2014-54498-R and MDM-2014-0377, COST MP16218 nanocohybri, ERC PNICTEYES Grant Agreement No. 679080, and Departamento Administrativo de Ciencia, Tecnología e Innovación, COLCIENCIAS (Colombia), Programa doctorados en el exterior and convocatoria 568-2012, as well as Comunidad de Madrid through program Nanofrontmag-CM (Grant No. S2013/MIT-2850)

It has been recently shown [I. Errea, B. Rousseau, and A. Bergara, Phys. Rev. Lett. 106, 165501 (2011)] that the phonons of the high-pressure simple cubic phase of calcium are stabilized by strong quantum anharmonic effects. This was obtained by a fully ab initio implementation of the self-consistent harmonic approximation including explicitly anharmonic coefficients up to fourth order. The renormalized anharmonic phonons make possible to estimate the superconducting transition temperature in this system, and a sharp agreement with experiments is found. In this work, this analysis is extended in order to study the effect of anharmonicity in the isotope effect. According to our calculations, despite the huge anharmonicity in the system, the isotope coefficient is predicted to be 0.45, close to the 0.5 value expected for a harmonic BCSsuperconductor. ; I.E. is grateful to the Department of Education, Universities and Research of the Basque Government for financial support. The authors acknowledge financial support from UPV/EHU (Grant No. IT-366-07) and the Spanish Ministry of Science and Innovation (Grant No. FIS2010-19609-C02-00). ; Peer reviewed

The conventional solid-state reaction method was utilized to prepare a series of superconducting samples of the nominal composition Bi2-xPb0.3WxSr2Ca2Cu3O10+d with 0≤x≤0.5 of 50 nm particle size of tungsten sintered at 8500C for 140h in air . The influence of substitution with W NPs at bismuth (Bi) sites was characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and dc electrical resistivity. Room temperature X-ray diffraction analysis revealed that there exists two phases, i.e. Bi-(2223) and Bi-(2212), in addition to the impurity phases of (SrCa) 2Cu2O3, Sr2Ca2Cu7Oδ, Ca2PbO4, CaO, and WO. It was found that the crystallographic structure of all samples was orthorhombic. Lattice parameter values and the volume fraction of the (2223)-phase of the prepared samples were also calculated. The superconductivity transition temperature (Tc) for samples subjected to substitution with W NPs was found to be higher than that for the pure sample. The optimal value of W NPs content in (Bi, Pb)-2223 system was found to be at x=0.3.

In this work, the characteristics of the phase transition face-centered cubic crystal — homogeneous phase in
helium are calculated based on the correlation cell-cluster expansion. The theoretical data were compared
with experimental data and good agreement was obtained. It is discussed the use of data on phase transitions
in helium to estimate thermodynamic characteristics phase transition in a quantum system of hard spheres.

6 pags., 2 figs. -- ERRATUM: Publisher's Note: Simulating superluminal physics with superconducting circuit technology [Phys. Rev. A 96, 032121 (2017)] Carlos Sabín, Borja Peropadre, Lucas Lamata, and Enrique Solano Phys. Rev. A 96, 049904 (2017) ; We provide tools for the quantum simulation of superluminal motion with superconducting circuits. We show that it is possible to simulate the motion of a superconducting qubit at constant velocities that exceed the speed of light in the electromagnetic medium and the subsequent emission of Ginzburg radiation. We also consider possible setups for simulating the superluminal motion of a mirror, finding a link with the super-radiant phase transition of the Dicke model. ; Financial support from the Fundación General CSIC is acknowledged by C.S. We also acknowledge support from Spanish MINECO/FEDER FIS2015-69983-P and FIS2015- 70856-P, Ramón y Cajal Grant No. RYC-2012-11391, CAM PRICYT Project QUITEMAD+ S2013/ICE-2801, Basque Government IT986-16, and UPV/EHU UFI 11/55. ; Peer Reviewed

A variety of bulk high-entropy alloy superconductors have been recently discovered; however, for thin films, only the TaNbHfZrTi highentropy alloy system has been investigated for its superconducting properties. Here, (TiZrNbTa)1-xWx and (TiZrNbTa)1-xVx superconducting films have been produced by DC magnetron sputtering at different growth temperatures. The phase formation and superconducting behavior of these films depend on the content of alloying x and deposition temperature. A single body-centered cubic (bcc) phase can be formed in the low x range with enough driving energy for crystallinity, but phase transition between amorphous or two bcc structures is observed when increasing x. The highest superconducting transition temperature Tc reaches 8.0 K for the TiZrNbTa film. The superconducting transition temperature Tc of these films deposited at the same temperature decreases monotonically as a function of x. Increasing deposition temperature to 400 °C can enhance Tc for these films while retaining nearly equivalent compositions. Our experimental observations suggest that Tc of superconducting high entropy alloys relate to the atomic radii difference and electronegativity difference of involved elements beyond the valence electron number. ; Funding: Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; VINNOVA Competence Centre FunMat-II [2016-05156]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW-2020.0196]; Swedish Research Council [2021-03826]