Search results for "Length"
showing 10 items of 2188 documents
Scanning tunnelling spectroscopy study of paramagnetic superconducting β''-ET(4)[(H(3)O)Fe(C(2)O(4))(3)]·C(6)H(5)Br crystals.
2010
Scanning tunnelling spectroscopy (STS) and microscopy (STM) were performed on the paramagnetic molecular superconductor β''-ET(4)[(H(3)O)Fe(C(2)O(4))(3)]·C(6)H(5)Br. Under ambient pressure, this compound is located near the boundary separating superconducting and insulating phases of the phase diagram. In spite of a strongly reduced critical temperature T(c) (T(c) = 4.0 K at the onset, zero resistance at T(c) = 0.5 K), the low temperature STS spectra taken in the superconducting regions show strong similarities with the higher T(c) ET κ-derivatives series. We exploited different models for the density of states (DOS), with conventional and unconventional order parameters to take into accoun…
Resistive state triggered by vortex entry in YBa 2 Cu 3 O 7−δ nanostructures
2014
We have realized YBa2Cu3O7-delta nanowires and nano Superconducting Quantum Interference Devices (nanoSQUID). The measured temperature dependence of the wire resistances below the superconducting transition temperature has been analyzed using a thermally activated vortex entry model valid for wires wider than the superconducting coherence length. The extracted zero temperature values of the London penetration depth, lambda(0) similar or equal to 270 +/- 15 nm, are in good agreement with the value obtained from critical current modulations as a function of an externally applied magnetic field in a nanoSQUID implementing two nanowires.
Phase Slip Phenomena in Ultra-Thin Superconducting Wires
2006
We present results on phase-slip phenomena in a superconducting wire which can be considered as quasi-one dimensional (1D) if its characteristic transverse dimension \( \sqrt \sigma\) (√ being the cross section) is smaller than the coherence length Λ(T). The shape of the bottom part of the resistive transition R(T) of a 1D superconducting strip is described by the model of phase slips activation. If the wire is infinitely long, then there is always a finite probability that a small part of the sample is instantly driven normal.
Length-scale-dependent vortex-antivortex unbinding in epitaxialBi2Sr2CaCu2O8+δfilms
1998
The supercurrent transport properties of epitaxial ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ films in zero applied magnetic field were investigated in a temperature interval of \ensuremath{\approx}20 K below the mean-field critical temperature ${T}_{c0}.$ The modification of the shape of the $I\ensuremath{-}V$ curves observed by varying the temperature was explained in terms of vortex-fluctuation-induced layer decoupling and vortex-antivortex unbinding, revealing a strong probing-length dependence. The change of the effective dimensionality of thermally excited vortices involved in the dissipation process leads to the appearance of …
Field dependence of the vortex core size probed by scanning tunneling microscopy
2016
We study the spatial distribution of the density of states (DOS) at zero bias N(r) in the mixed state of single and multigap superconductors. We provide an analytic expression for N(r) based on deGennes' relationship between DOS and the order parameter that reproduces well scanning tunneling microscopy (STM) data in several superconducting materials. In the single gap superconductor β-Bi2Pd, we find that N(r) is governed by a length scale ξH=φ0/2πH, which decreases in rising fields. The vortex core size C, defined via the slope of the order parameter at the vortex center, C (dΔ/dr|r→0)-1, differs from ξH by a material dependent numerical factor. The new data on the tunneling conductance and…
Nonlocal pure spin current injection via quantum pumping and crossed Andreev reflection
2005
A pure spin current injector is proposed based on adiabatic pumping and crossed normal/Andreev reflection. The device consists of a three-terminal ferromagnet-superconductor-semiconductor system in which the injection of a pure spin current is into the semiconductor which is coupled to the superconductor within a coherence length away from the ferromagnet enabling the phenomena of crossed normal /Andreev reflection to operate. Quantum pumping is induced by adiabatically modulating two independent parameters of the ferromagnetic lead, namely the magnetization strength and the strength of coupling between the ferromagnet and the superconductor. The competition between the normal/Andreev refle…
Growth, domain structure, and atomic adsorption sites of hBN on the Ni(111) surface
2021
One of the most important functionalities of the atomically thin insulator hexagonal boron nitride (hBN) is its ability to chemically and electronically decouple functional materials from highly reactive surfaces. It is therefore of utmost importance to uncover its structural properties on surfaces on an atomic and mesoscopic length scale. In this paper, we quantify the relative coverages of structurally different domains of a hBN layer on the Ni(111) surface using low-energy electron microscopy and the normal incidence x-ray standing wave technique. We find that hBN nucleates on defect sites of the Ni(111) surface and predominantly grows in two epitaxial domains that are rotated by ${60}^{…
Detecting self-similarity in surface microstructures
2000
The relative configurational entropy per cell as a function of length scale is a sensitive detector of spatial self-similarity. For Sierpinski carpets the equally separated peaks of the above function appear at the length scales that depend on the kind of the carpet. These peaks point to the presence of self-similarity even for randomly perturbed initial fractal sets. This is also demonstrated for the model population of particles diffusing over the surface considered by Van Siclen, Phys. Rev. E 56 (1997) 5211. These results allow the subtle self-similarity traces to be explored.
A new liquid surface neutron reflectometer and its application to the study of DPPC in a monolayer at the air/water interface
1991
A constant wavelength neutron reflectometer is described. Using this reflectometer, the neutron reflectivities from phosphatidylcholine monolayers in the highly condensed LC phase on ultra pure H2O and D2O have been measured on a Wilhelmy film balance. The neutron reflectivities have been carefully compared with those obtained by the X-ray method applied to the same monolayer under similar conditions. A new approach to analyzing a combined set of data composed of X-ray and neutron reflectivities has been used. From the analysis it is concluded that despite their limited qz range neutron reflectivities are as essential as X-ray reflectivities for the unique determination of the monolayer str…
Computer-Controlled Experiments in the Surface Forces Apparatus with a CCD-Spectrograph
1996
We present a computer-controlled technique to measure the distance-dependent forces in the surface forces apparatus. The power of our setup is shown by a measurement of the repulsive forces between mica surfaces immersed in a 0.01 M NaCl solution. At close distances we find an oscillatory force with a periodicity of 0.30 nm, which roughly corresponds to the diameter of a water molecule. For the distance determination we use the standard interferometric technique: the interferometer consists of a medium sandwiched between two mica sheets of equal thickness silvered on the backside. The surface separation is measured by comparing the resonance wavelength to the one obtained from contacting m…