Search results for "Multidisciplinary"
showing 10 items of 4640 documents
Possible light-induced superconductivity in K3C60 at high temperature.
2015
The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity. Nonlinear excitation of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc. This effect was accompanied by the disruption of competing charge-density-wave correlations, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increas…
Coherent quantum phase slip
2012
A hundred years after discovery of superconductivity, one fundamental prediction of the theory, the coherent quantum phase slip (CQPS), has not been observed. CQPS is a phenomenon exactly dual to the Josephson effect: whilst the latter is a coherent transfer of charges between superconducting contacts, the former is a coherent transfer of vortices or fluxes across a superconducting wire. In contrast to previously reported observations of incoherent phase slip, the CQPS has been only a subject of theoretical study. Its experimental demonstration is made difficult by quasiparticle dissipation due to gapless excitations in nanowires or in vortex cores. This difficulty might be overcome by usin…
Detection of Geometric Phases in Superconducting Nanocircuits
2000
When a quantum mechanical system undergoes an adiabatic cyclic evolution it acquires a geometrical phase factor in addition to the dynamical one. This effect has been demonstrated in a variety of microscopic systems. Advances in nanotechnologies should enable the laws of quantum dynamics to be tested at the macroscopic level, by providing controllable artificial two-level systems (for example, in quantum dots and superconducting devices). Here we propose an experimental method to detect geometric phases in a superconducting device. The setup is a Josephson junction nanocircuit consisting of a superconducting electron box. We discuss how interferometry based on geometrical phases may be real…
Superconductivity mediated by spin fluctuations in the heavy-fermion compound UPd2 Al3
1999
It is well known that any weak attractive electron–electron interaction in metals can in principle cause the formation of Cooper pairs, which then condense into a superconducting ground state1. In conventional superconductors, this attractive interaction is mediated by lattice vibrations (phonons). But for the heavy-fermion and high-temperature superconductors, alternative pairing interactions are considered to be possible2. For example, the low-temperature properties of heavy-fermion systems are dominated by antiferromagnetic spin fluctuations, which have been considered theoretically3 as a possible cause for Cooper-pair formation. This picture recently received some experimental support: …
Strong vacuum squeezing from bichromatically driven Kerrlike cavities: from optomechanics to superconducting circuits
2015
AbstractSqueezed light, displaying less fluctuation than vacuum in some observable, is key in the flourishing field of quantum technologies. Optical or microwave cavities containing a Kerr nonlinearity are known to potentially yield large levels of squeezing, which have been recently observed in optomechanics and nonlinear superconducting circuit platforms. Such Kerr-cavity squeezing however suffers from two fundamental drawbacks. First, optimal squeezing requires working close to turning points of a bistable cycle, which are highly unstable against noise thus rendering optimal squeezing inaccessible. Second, the light field has a macroscopic coherent component corresponding to the pump, ma…
Origin of high critical currents in YBa2Cu3O7−δ superconducting thin films
1999
Thin films of the high-temperature superconductor YBa2Cu3O7−δ exhibit both a large critical current (the superconducting current density generally lies between 1011 and 1012 A m−2 at 4.2 K in zero magnetic field) and a decrease in such currents with magnetic field that point to the importance of strong vortex pinning along extended defects1,2. But it has hitherto been unclear which types of defect—dislocations, grain boundaries, surface corrugations and anti-phase boundaries—are responsible. Here we make use of a sequential etching technique to address this question. We find that both edge and screw dislocations, which can be mapped quantitatively by this technique, are the linear defects t…
Critical current modulation induced by an electric field in superconducting tungsten-carbon nanowires
2021
The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. This phenomenon is investigated throughout the fabrication and electrical characterization of superconducting tungsten-carbon (W-C) nanostructures grown by Ga+ focused ion beam induced deposition (FIBID). In a 45 nm-wide, 2.7 μm-long W-C nanowire, an increasing side-gate voltage is found to progressively reduce the critical current of the device, down to a full suppression of the superconducting state below its critical temperature. This modulation is accounted for by the squeezing of the superconducting current by the electric field within a theoretical model based on th…
Quantum phase slip phenomenon in ultra-narrow superconducting nanorings
2012
The smaller the system, typically - the higher is the impact of fluctuations. In narrow superconducting wires sufficiently close to the critical temperature Tc thermal fluctuations are responsible for the experimentally observable finite resistance. Quite recently it became possible to fabricate sub-10 nm superconducting structures, where the finite resistivity was reported within the whole range of experimentally obtainable temperatures. The observation has been associated with quantum fluctuations capable to quench zero resistivity in superconducting nanowires even at temperatures T-->0. Here we demonstrate that in tiny superconducting nanorings the same phenomenon is responsible for s…
Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system.
2015
A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, Tc. The highest Tc that has been achieved to date is in the copper oxide system: 133 kelvin at ambient pressure and 164 kelvin at high pressures. As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide for achieving high Tc with no theoretical upper bound--all that is needed is a favourable combination of …
Author Correction: Induced unconventional superconductivity on the surface states of Bi2Te3 topological insulator
2018
Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p x + ip y wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi2Te3 topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral p x + ip y component. The magnetic field pattern of the junctions shows a dip at zero externally applied magneti…