Vortex Imaging in Novel Superconductors (original) (raw)
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Vortex imaging in unconventional superconductors
Physica C-Superconductivity and Its Applications, 2012
The real space imaging of vortices in unconventional superconductors not only provides important information about the effectiveness of flux pinning that can inform high current applications, but also yields crucial insights into the form of the superconducting order parameter. For example, the structure of the vortex lattice reflects effective mass and order parameter anisotropies within the material, and profiles of isolated vortices provide a local measure of the magnetic penetration depth that can be used to infer the superfluid density. We describe here the analysis of recent studies whereby state-of-the-art scanning Hall probe microscopy (SHPM) has been used to perform vortex-resolved magnetic imaging on two distinct families of unconventional superconductors. Two sets of results will be analysed in detail; (i) vortex lattice structural transitions in the p-wave superconductor Sr 2 RuO 4 that reflect underlying anisotropies in the system and (ii) a quantitative analysis of vortex profiles in Co-doped 122 pnictide superconductors (SrFe 2Àx Co x As 2 & BaFe 2Àx Co x As 2 ) that allows one to infer the temperature-dependent superfluid density. The latter has then been compared with predictions for different order parameter models for a multiband superconductor.
Vortex Nanoliquid in High-Temperature Superconductors
Physical Review Letters, 2004
Using a differential magneto-optical technique to visualize the flow of transport currents, we reveal a new delocalization line within the reversible vortex liquid region in the presence of a low density of columnar defects. This line separates a homogeneous vortex liquid, in which all the vortices are delocalized, from a heterogeneous ''nanoliquid'' phase, in which interconnected nanodroplets of vortex liquid are caged in the pores of a solid skeleton formed by vortices pinned on columnar defects. The nanoliquid phase displays high correlation along the columnar defects but no transverse critical current.
Direct Observation of a Superconducting Vortex Diode
arXiv (Cornell University), 2023
The interplay between magnetism and superconductivity can lead to unconventional proximity and Josephson effects. A related phenomenon that has recently attracted considerable attention is the superconducting diode effect, in which a non-reciprocal critical current emerges. Although superconducting diodes based on superconducting/ferromagnetic (S/F) bilayers were demonstrated more than a decade ago, the precise underlying mechanism remains unclear. While not formally linked to this effect, the Fulde-Ferrell-Larkin-Ovchinikov (FFLO) state is a plausible mechanism, due to the 2-fold rotational symmetry breaking caused by the finite center-of-mass-momentum of the Cooper pairs. Here, we directly observe, for the first time, a tunable superconducting vortex diode in Nb/EuS (S/F) bilayers. Based on our nanoscale SQUID-on-tip (SOT) microscope and supported by in-situ transport measurements, we propose a theoretical model that captures our key results. Thus, we determine the origin for the vortex diode effect, which builds a foundation for new device concepts.
μSR studies of the vortex state in type-II superconductors
Reviews of Modern Physics, 2000
The authors present a review of recent muon spin rotation (SR) studies of the vortex state in type-II superconductors. There are significant gaps in our understanding of this unusual phase of matter, especially in unconventional superconductors, for which the description of the vortex structure is a subject of great controversy. The SR technique provides a sensitive local probe of the spatially inhomogeneous magnetic field associated with the vortex state. For the case of a regular vortex lattice, the magnetic penetration depth and the coherence length can be simultaneously extracted from the measured internal field distribution. The penetration depth is directly related to the density of superconducting carriers in the material, and measurements of its variation with temperature, magnetic field, and impurities can provide essential information on the symmetry of the order parameter. The coherence length measured with SR is the length scale for spatial variations of the order parameter within a vortex core. A primary goal of this review article is to show that measurements of these fundamental length scales are fairly robust with respect to the details of how the field distribution is modeled. The reliability of the results is demonstrated by a comparison of the SR experiments with relevant theories and with other experimental techniques. The authors also review SR measurements that have focused on the study of pinning-induced spatial disorder and vortex fluctuation phenomena. The SR technique has proven to be a powerful tool for investigating exotic vortex phases, where vortex transitions are directly observable from changes in the SR line shape. Particular emphasis is given to SR experiments performed on high-temperature superconductors since high-quality single crystals have become available. CONTENTS I. Introduction 769 II. The SR Technique 770 A. Asymmetry spectra 771 B. The depolarization function 772 C. Four-counter complex muon polarization 773 D. The rotating reference frame 773 E. The fast Fourier transform 773 F. Low-background apparatus 775 III. Modeling the Internal Magnetic-Field Distribution 776 A. Gaussian field distribution 776 B. Vortex lattice in a conventional s-wave superconductor 777 1. London model 777 2. Vortex core structure 778 3. Temperature dependence of the vortex core size 778 4. Field dependence of the vortex core size 779 5. Vortex core symmetry 779 6. Ginzburg-Landau model 780 7. Vortex lattice geometry 780 C. Vortex lattice in a d x 2 Ϫy 2-wave superconductor 781 1. Two-component Ginzburg-Landau models 781 2. Quasiclassical predictions 782 3. Bogoliubov-de Gennes calculations 782 4. London models 782 5. Experimental observations 783 D. Pinning and thermal fluctuations 785 1. Vortex pinning 785 2. Thermal depinning and vortex lattice melting 785 3. Pancake vortices 787 4. The peak effect 792 IV. The Magnetic Penetration Depth 792 A. Temperature dependence 792 1. Meissner state 792 2. Vortex state 793 B. Magnetic-field dependence 796 1. Nonlinear effects 796 2. Nonlocal effects 797 3. Extension to the vortex state 797 4. Charge and impurity doping 799 V. The Vortex Core Size 801 A. Magnetic-field dependence 802 B. Temperature dependence 805 VI. Summary 806 Acknowledgments 806 References 807
Nature, 2001
Puzzling aspects of high-transition-temperature (high-Tc) superconductors include the prevalence of magnetism in the normal state and the persistence of superconductivity in high magnetic fields. Superconductivity and magnetism generally are thought to be incompatible, based on what is known about conventional superconductors. Recent results, however, indicate that antiferromagnetism can appear in the superconducting state of a high-Tc superconductor in the presence of an applied magnetic field. Magnetic fields penetrate a superconductor in the form of quantized flux lines, each of which represents a vortex of supercurrents. Superconductivity is suppressed in the core of the vortex and it has been suggested that antiferromagnetism might develop there. Here we report the results of a high-field nuclear-magnetic-resonance (NMR) imaging experiment in which we spatially resolve the electronic structure of near-optimally doped YBa2Cu3O7-delta inside and outside vortex cores. Outside the ...
Physical Review B, 2021
Harnessing the properties of vortices in superconductors is crucial for fundamental science and technological applications; thus, it has been an ongoing goal to locally probe and control vortices. Here, we use a scanning probe technique that enables studies of vortex dynamics in superconducting systems by leveraging the resonant behavior of a raster-scanned, magnetic-tipped cantilever. This experimental setup allows us to image and control vortices, as well as extract key energy scales of the vortex interactions. Applying this technique to lattices of superconductor island arrays on a metal, we obtain a variety of striking spatial patterns that encode information about the energy landscape for vortices in the system. We interpret these patterns in terms of local vortex dynamics and extract the relative strengths of the characteristic energy scales in the system, such as the vortex-magnetic field and vortex-vortex interaction strengths, as well as the vortex chemical potential. We also demonstrate that the relative strengths of the interactions can be tuned and show how these interactions shift with an applied bias. The high degree of tunability and local nature of such vortex imaging and control not only enable new understanding of vortex interactions, but also have potential applications in more complex systems such as those relevant to quantum computing.
Search for Vortex Unbinding in Two-Dimensional Superconductors
Physical Review Letters, 1981
luminescence has also been observed from the rough metal surfaces. The mechanism leading to such luminescence is not yet understood. We thank Professor R. K. Chang for providing information about electrolytic cycling on Au and Cu. This work was supported by the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy under Contract No. W-7405-ENG-48. One of us (A.R.B.d.c.
Vortex dynamics and correlated disorder in high-Tc superconductors
Physica A: Statistical Mechanics and its Applications, 1993
ty a contractor of the US. Government under contract No. W-31-104ENG-38. Accordingly. the U.S. Government retains a nonexduske. royaky-lree llcense to pubkh of reproduce the published form of this wntn'bulkn. or aWow DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed. or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
Vortex dynamics in magnetic and superconducting nanostructurs
2012
To my family, for your love, compassion and giving; every single word written here is dedicated to you. Love you so much. A Amjad Al-Taleb, por compartir los buenos y malos momentos. Por tu sinceridad y tu apoyo, gracias ¨Angel párpado¨. A los de Bajas Temperaturas que compartimos más que trabajar en frio, A los cachondos que siempre están ahí para ayudar: Jose Augusto y Roberto, muchas gracias. Y también a Manuel, Ana, Prasana, Charalmbos, y Siya. Y especialmente a Merzak que siempre me ha apoyado, gracias amigo por animarme tanto. Por tu humildad y la amistad que siempre has hecho que la comida entre mejor acompañándola con tus chistes. Gracias por todos estos años y lo que vendrán más. Tomás. A los que ya se han marchado pero han dejado sus huellas Eduardo (gracias por tu actitud de apoyo y ayuda, y la bici), Guillermo y Andrés. A mis primeros amigos en España que casi me adoptaron, por los buenos recuerdos cariñosos y alegres que me habies dado, A los maravillosos Caludio Polini,