54 research outputs found
Penetration of Andreev bound states into the ferromagnet in a SrRuO/(110)YBaCuO bilayer: a scanning tunneling spectroscopy study
Scanning tunneling spectroscopy of thin epitaxial
ferromagnet/superconductor bilayers,
reveal a clear penetration of the Andreev bound states into the ferromagnetic
layer. The penetration is manifested in the density of states of the
ferromagnet as a split zero bias conductance peak with an imbalance between
peak heights. Our data indicate that the splitting occurs at the superconductor
side as a consequence of induced magnetization, confirming recent theoretical
predictions. The imbalance is attributed to the spin polarization in the
ferromagnet.Comment: 4 figure
Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor
Considerable evidence for proximity-induced triplet superconductivity on the
ferromagnetic side of a superconductor-ferromagnet (S-F) interface now exists;
however, the corresponding effect on the superconductor side has hardly been
addressed. We have performed scanning tunneling spectroscopy measurements on
NbN superconducting thin films proximity coupled to the half-metallic
ferromagnet La2/3Ca1/3MnO3 (LCMO) as a function of magnetic field. We have
found that at zero and low applied magnetic fields the tunneling spectra on NbN
typically show an anomalous gap structure with suppressed coherence peaks and,
in some cases, a zero-bias conductance peak. As the field increases to the
magnetic saturation of LCMO where the magnetization is homogeneous, the spectra
become more BCS-like and the critical temperature of the NbN increases,
implying a reduced proximity effect. Our results therefore suggest that
triplet-pairing correlations are also induced in the S side of an S-F bilayer.Comment: 12 pages, 3 figure
Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study
We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on
top of which ferromagnetic SRO islands were grown epitaxially in-situ. When
measured on the ferromagnetic islands, the density of states exhibits small
gap-like features consistent with the expected short range penetration of the
order parameter into the ferromagnet. However, anomalous split-gap structures
are measured on the superconductor in the vicinity of ferromagnetic islands.
This observation may provide evidence for the recently predicted induced
magnetization in the superconductor side of a superconductor/ ferromagnet
junction. The length scale of the effect inside the superconductor was found to
be an order of magnitude larger than the superconducting coherence length. This
is inconsistent with the theoretical prediction of a penetration depth of only
a few superconducting coherence lengths. We discuss a possible origin for this
discrepancy
Periodic negative differential conductance in a single metallic nano-cage
We report a bi-polar multiple periodic negative differential conductance
(NDC) effect on a single cage-shaped Ru nanoparticle measured using scanning
tunneling spectroscopy. This phenomenon is assigned to the unique
multiply-connected cage architecture providing two (or more) defined routes for
charge flow through the cage. This, in turn, promotes a self- gating effect,
where electron charging of one route affects charge transport along a
neighboring channel, yielding a series of periodic NDC peaks. This picture is
established and analyzed here by a theoretical model
Anomalous proximity effect in gold coated (110) films: Penetration of the Andreev bound states
Scanning tunneling spectroscopy of (110) bi-layers
reveal a proximity effect markedly different from the conventional one. While
proximity-induced mini-gaps rarely appear in the Au layer, the Andreev bound
states clearly penetrate into the metal. Zero bias conductance peaks are
measured on Au layers thinner than 7 nm with magnitude similar to those
detected on the bare superconductor films. The peaks then decay abruptly with
Au thickness and disappear above 10 nm. This length is shorter than the normal
coherence length and corresponds to the (ballistic) mean free path.Comment: 5 prl format pages, 4 figures, to be published in PR
Control of charging in resonant tunneling through InAs nanocrystal quantum dots
Tunneling spectroscopy of InAs nanocrystals deposited on graphite was
measured using scanning tunneling microscopy, in a double-barrier
tunnel-junction configuration. The effect of the junction symmetry on the
tunneling spectra is studied experimentally and modeled theoretically. When the
tip is retracted, we observe resonant tunneling through the nanocrystal states
without charging. This is in contrast to previous measurements on similar
nanocrystals anchored to gold by linker molecules, where charging took place.
Charging is regained upon reducing the tip-nanocrystal distance, making the
junctions more symmetric. The effect of voltage distribution between the
junctions on the measured spectra is also discussed.Comment: submitte
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