283 research outputs found
Zeeman-limited Superconductivity in Crystalline Al Films
We report the evolution of the Zeeman-mediated superconducting phase diagram
(PD) in ultra-thin crystalline Al films. Parallel critical field measurements,
down to 50 mK, were made across the superconducting tricritical point of films
ranging in thickness from 7 ML to 30 ML. The resulting phase boundaries were
compared with the quasi-classical theory of a Zeeman-mediated transition
between a homogeneous BCS condensate and a spin polarized Fermi liquid. Films
thicker than 20 ML showed good agreement with theory, but thinner films
exhibited an anomalous PD that cannot be reconciled within a homogeneous BCS
framework.Comment: 8 pages, 9 figure
Visualizing Quantum Well State Perturbations of Metallic Thin Films near Stacking Fault Defects
We demonstrate that quantum well states (QWS) of thin Pb films are highly
perturbed within the proximity of intrinsic film defects. Scanning Tunneling
Spectroscopy (STM/STS) measurements indicate that the energy of these states
have a strong distance dependence within 4 nm of the defect with the strongest
energetic fluctuations equaling up to 100 meV. These localized perturbations
show large spatially-dependent asymmetries in the LDOS around the defect site
for each corresponding quantum well state. These energetic fluctuations can be
described by a simple model which accounts for fluctuations in the confinement
potential induced by topographic changes.Comment: Updated Versio
Observation of simultaneous fast and slow light
We present a microresonator-based system capable of simultaneously producing
time-advanced and time-delayed pulses. The effect is based on the combination
of a sharp spectral feature with two orthogonally-polarized propagating
waveguide modes. We include an experimental proof-of-concept implementation
using a silica microsphere coupled to a tapered optical fiber and use a
time-domain picture to interpret the observed delays. We also discuss potential
applications for future all-optical networks.Comment: 6 pages, 5 figure
Interrogating the superconductor Ca10(Pt4As8)(Fe2-xPtxAs2)5 Layer-by-layer
Ever since the discovery of high-Tc superconductivity in layered cuprates,
the roles that individual layers play have been debated, due to difficulty in
layer-by-layer characterization. While there is similar challenge in many
Fe-based layered superconductors, the newly-discovered Ca10(Pt4As8)(Fe2As2)5
provides opportunities to explore superconductivity layer by layer, because it
contains both superconducting building blocks (Fe2As2 layers) and intermediate
Pt4As8 layers. Cleaving a single crystal under ultra-high vacuum results in
multiple terminations: an ordered Pt4As8 layer, two reconstructed Ca layers on
the top of a Pt4As8 layer, and disordered Ca layer on the top of Fe2As2 layer.
The electronic properties of individual layers are studied using scanning
tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for
each surface. Remarkably superconducting coherence peaks are seen only on the
ordered Ca/Pt4As8 layer. Our results indicate that an ordered structure with
proper charge balance is required in order to preserve superconductivity
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