1,721,018 research outputs found
Spontaneous magnetic moments in YBa2Cu3O7-x thin films
No full textWe have observed spontaneous magnetic moments with random signs in c-axis-oriented thin films of the high-Tc cuprate superconductor YBa2Cu3O7-d , imaged with a scanning superconducting quantum interference device microscope. These moments arise when the samples become superconducting, and appear to be associated with nonferromagnetic defects in the films. In contrast with granular high-Tc samples, which also show spontaneous moments with random signs, the present samples shield diamagnetically
Weak links in high critical temperature superconductors
No full textThe traditional distinction between tunnel and highly transmissive barriers does not currently hold for high critical temperature superconducting Josephson junctions, both because of complicated materials issues and the intrinsic properties of high temperature superconductors (HTS). An intermediate regime, typical of both artificial superconductor– barrier–superconductor structures and of grain boundaries, spans several orders of magnitude in the critical current density and specific resistivity. The physics taking place at HTS surfaces and interfaces is rich, primarily because of phenomena associated with d wave order parameter (OP) symmetry. These phenomena include Andreev bound states, the presence of the second harmonic in the critical current versus phase relation, a doubly degenerate state, time reversal symmetry breaking and the possible presence of an imaginary component of the OP. All these effects are regulated by a series of transport mechanisms, whose rules of interplay and relative activation are unknown. Some transport mechanisms probably have common roots, which are not completely clear and possibly related to the intrinsic nature of high-TC superconductivity. The d-wave OP symmetry gives unique properties to HTS weak links, which do not have any analogy with systems based on other superconductors. Even if the HTS structures are not optimal, compared with low critical temperature superconductor Josephson junctions, the state of the art allows the realization of weak links with unexpectedly high quality quantum properties, which open interesting perspectives for the future. The observation of macroscopic quantum tunnelling and the qubit proposals represent significant achievements in this direction. In this review we attempt to encompass all the above aspects, attached to a solid experimental basis of junction concepts and basic properties, along with a flexible phenomenological background, which collects ideas on the Josephson effect in the presence of d-wave pairing for different types of barriers
Intrinsic and extrinsic d-wave effects in YBaCuO grain boundary Josephson junctions: implications for pi-circuitry
No full textWe have investigated the properties of biepitaxial YBa2Cu3O72d grain boundary Josephson junctions, which appear to be characterized by low barrier transmission probabilities. Extrinsic and intrinsic d-wave effects are discussed within the framework of novel designs for p-circuitry and qubits. The absence of spontaneous magnetization and of the consequent additional noise, in a wide range of experimental conditions, seems to be encouraging for designs of ‘‘quiet’’ device
CONSEQUENCES OF UNCONVENTIONAL ORDER PARAMETER SYMMETRY - HIGH CRITICAL TEMPERATURE STRUCTURES
No full textBARONE A. Invited at THE NOBEL JUBELEE SYMPOSIUM "CONDENSATION AND COHERENCE IN CONDENSED SYSTEMS"
CONSEQUENCES OF UNCONVENTIONAL ORDER PARAMETER SYMMETRY - HIGH CRITICAL TEMPERATURE STRUCTURES
No full textBARONE A. Invited at THE NOBEL JUBELEE SYMPOSIUM "CONDENSATION AND COHERENCE IN CONDENSED SYSTEMS"
CONSEQUENCES OF UNCONVENTIONAL ORDER PARAMETER SYMMETRY - HIGH CRITICAL TEMPERATURE STRUCTURES
No full textBARONE A. Invited at THE NOBEL JUBELEE SYMPOSIUM "CONDENSATION AND COHERENCE IN CONDENSED SYSTEMS"
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tunneling Measurements of the cuprate superconductors
No full textAfter a very brief description of what has been learned from tunneling measurements in conventional
superconductors, we provide an overview of general concepts relevant to the cuprates. These include
the types of junction structures used, effects due to variable junction transparency from the point contact
to the tunneling regimes, proximity effects, Andreev scattering, unconventional pairing symmetry,
and possible broken time reversal symmetry. We describe the various methods used for obtaining tunneling
junctions in the high-temperature cuprate superconductors. We describe how the unconventional
pairing symmetry of the cuprate superconductors leads to π-rings and 0–π-junctions, and how these
effects have been used to determine that the gap in the cuprates has predominantly dx2−y2 pairing symmetry.
We then turn to tunneling spectroscopy. The superconducting gap, the pseudogap, and zero bias
conductance peaks are closely interrelated. The superconducting gap and zero bias conductance peaks
can be understood in terms of transport between electrodes with dx2−y2 pairing symmetry through low
and high transmissivity barriers. It is controversial whether the pseudogap represents an order competing
with superconductivity or preformed Cooper pairs. Similarly, there are many indications of broken
time reversal symmetry in tunneling spectroscopy measurements, but not in measurements of π-ring
and 0–π-junctions. Conductivity modulations in atomically resolved scanning tunneling spectroscopy
certainly can arise from quasiparticle interference effects, but there is also evidence for nondispersive
conductivity modulations, expected from stripe models. We describe tunneling evidence for strong coupling
effects involving phonon and magnon interactions with the quasiparticles in the superconducting
state
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