2,047 research outputs found
Detrended fluctuation analysis on the correlations of complex networks under attack and repair strategy
We analyze the correlation properties of the Erdos-Renyi random graph (RG)
and the Barabasi-Albert scale-free network (SF) under the attack and repair
strategy with detrended fluctuation analysis (DFA). The maximum degree k_max,
representing the local property of the system, shows similar scaling behaviors
for random graphs and scale-free networks. The fluctuations are quite random at
short time scales but display strong anticorrelation at longer time scales
under the same system size N and different repair probability p_re. The average
degree , revealing the statistical property of the system, exhibits
completely different scaling behaviors for random graphs and scale-free
networks. Random graphs display long-range power-law correlations. Scale-free
networks are uncorrelated at short time scales; while anticorrelated at longer
time scales and the anticorrelation becoming stronger with the increase of
p_re.Comment: 5 pages, 4 figure
Suppression of Superconductivity by Twin Boundaries in FeSe
Low-temperature scanning tunneling microscopy and spectroscopy are employed
to investigate twin boundaries in stoichiometric FeSe films grown by molecular
beam epitaxy. Twin boundaries can be unambiguously identified by imaging the
90{\deg} change in the orientation of local electronic dimers from Fe site
impurities on either side. Twin boundaries run at approximately 45{\deg} to the
Fe-Fe bond directions, and noticeably suppress the superconducting gap, in
contrast with the recent experimental and theoretical findings in other iron
pnictides. Furthermore, vortices appear to accumulate on twin boundaries,
consistent with the degraded superconductivity there. The variation in
superconductivity is likely caused by the increased Se height in the vicinity
of twin boundaries, providing the first local evidence for the importance of
this height to the mechanism of superconductivity.Comment: 6 pages, 7 figure
Visualizing the elongated vortices in -Ga nanostrips
We study the magnetic response of superconducting -Ga via low
temperature scanning tunneling microscopy and spectroscopy. The magnetic vortex
cores rely substantially on the Ga geometry, and exhibit an unexpectedly-large
axial elongation with aspect ratio up to 40 in rectangular Ga nano-strips
(width 100 nm). This is in stark contrast with the isotropic circular
vortex core in a larger round-shaped Ga island. We suggest that the unusual
elongated vortices in Ga nanostrips originate from geometric confinement effect
probably via the strong repulsive interaction between the vortices and Meissner
screening currents at the sample edge. Our finding provides novel conceptual
insights into the geometrical confinement effect on magnetic vortices and forms
the basis for the technological applications of superconductors.Comment: published in Phys. Rev. B as a Rapid Communicatio
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