71 research outputs found
Suppressed superconductivity in ultrathin Mo2N films due to pair-breaking at the interface
A strong disorder characterized by a small product of the Fermi vector kF and
the electron mean free l drives superconductors towards insulating state. Such
disorder can be introduced by making the films very thin. Here, we present 3-nm
Mo2N film with k_F*l ~ 2 with a resistive superconducting transition
temperature Tc = 2 K heavily suppressed in comparison with the bulk Tc.
Superconducting density of states (DOS) with smeared gap-like peaks and in-gap
states, so called Dynes DOS, is observed by the low temperature tunneling
spectroscopy despite a sharp resistive transition. By scanning tunneling
microscope the spectral maps are obtained and related to the surface
topography. The maps show a spatial variation of the superconducting energy gap
on the order of 20 % which is not accidental but well correlates with the
surface corrugation: protrusions reveal larger gap, smaller spectral smearing
and smaller in-gap states. In agreement with our previous measurements on
ultrathin MoC films we suggest that the film-substrate interface introducing
the local pair-breaking is responsible for the observed effects and generally
for the suppression of the superconductivity in these ultrathin films.Comment: Manuscript with 3 Figure
Persistent Oscillations of X-ray Speckles: Pt (001) Step Flow
We have performed coherent x-ray scattering experiments on the hexagonally
reconstructed Pt (001) surface to study the temperature-dependent surface
dynamics. By correlating speckle patterns collected at the (001) anti-Bragg
position we are able to measure surface dynamics when the averaged incoherent
x-ray scattering appears static. In the temperature range above the rotational
epitaxy transition and below the roughening transition (1750 K - 1830 K), we
have observed well-defined oscillatory autocorrelations of speckles that
persist for tens of minutes, in addition to the expected thermal decorrelation.
The observed oscillations indicate surface dynamics due to "step-flow" motion.
This is shown with a simple model in which the phase of the scattered x-rays
from the steps within the illumination area is retained in the coherent x-ray
scattering. This demonstrates a possibility that x-ray speckles can be used to
monitor the real-space real-time evolution of surfaces in addition to the
traditional decorrelation measurements.Comment: 12 pages, 3 figure
Disorder- and magnetic field-tuned fermionic superconductor-insulator transition in MoN thin films. Transport and STM studies
Superconductor-insulator transition (SIT) driven by disorder and transverse
magnetic field has been investigated in ultrathin MoN films by means of
transport measurements and scanning tunneling microscopy and spectroscopy. Upon
decreasing thickness, the homogeneously disordered films show increasing sheet
resistance Rs, shift of the superconducting transition Tc to lower temperatures
with the 3 nm MoN being the last superconducting film and thinner films already
insulating. Fermionic scenario of SIT is evidenced by applicability of the
Finkelsteins model, by the fact that Tc and the superconducting gap are coupled
with a constant ratio, and by the spatial homogeneity of the superconducting
and electronic characteristics. The logarithmic anomaly found in the tunneling
spectra of the non-superconducting films is further enhanced in increased
magnetic field due to the Zeeman spin effects driving the system deeper into
the insulating state and pointing also to fermionic SIT.Comment: Manuscript (6 Figures) including Supplemental Materials (7 Figures
Controlling the Transverse Magneto-Optical Kerr Effect in Cr/NiFe Bilayer Thin Films by Changing the Thicknesses of the Cr Layer
Here, we demonstrate the impact of ferromagnetic layer coating on controlling the magneto-optical response. We found that the transverse magneto-optical Kerr effect (TMOKE) signal and TMOKE hysteresis loops of Ni80Fe20 thin layers coated with a Cr layer show a strong dependence on the thickness of the Cr layer and the incidence angle of the light. The transmission and reflection spectra were measured over a range of incidence angles and with different wavelengths so as to determine the layers’ optical parameters and to explain the TMOKE behavior. The generalized magneto-optical and ellipsometry (GMOE) model based on modified Abeles characteristic matrices was used to examine the agreement between the experimental and theoretical results. A comprehensive theoretical and experimental analysis reveals the possibility to create a TMOKE suppression/enhancement coating at specific controllable incidence angles. This has potential for applications in optical microscopy and sensors
CO-induced lifting of Au (001) surface reconstruction
We report CO-induced lifting of the hexagonal surface reconstruction on Au
(001). Using in-situ surface x-ray scattering, we determined a
pressure-temperature phase diagram for the reconstruction and measured the
dynamical evolution of the surface structure in real time. Our observations
provide evidence that, under certain conditions, even macroscopic Au surfaces,
much larger than catalytic Au nanoparticles [M. Haruta, Catal. Today 36, 153
(1997)], can exhibit some of the reactive properties and surface transitions
observed in systems known to be catalytically active such as Pt (001).Comment: 4 Figures. Accepted as a Letter to Journal of Physical Chemistry
Anizotropy of Photoconductivity in BiOCl (X=Cl, Br, I) Single Crystals
Oxyhalides of bismuth BiOX (X = Cl, Br, I) are very interesting materials which find various applications as X-ray luminescent screens, as anti-Stokes converters, photocatalyst, usual luminophors and as photoconductive analyzer of linear polarized radiation in the 0.24 - 1.2 μm spectral region. The great interest for these materials is strongly related to the influence of dimensionality on the behaviour of physical properties (they are 2D structured materials). Bismuth oxyhalides are one of the V-VI-VII group compound semiconductors belonging to the tetragonal system. The structure of BiOX is known to have a layered structure, which is constructed by the combination of the halide ion layer and the bismuth oxygen layer. We present results of the study of photoconductivity spectra anisotropy of the BiOX single crystals
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