239 research outputs found
Preparation and properties of amorphous MgB/MgO superstructures: A new model disordered superconductor
In this paper we introduce a novel method for fabricating MgB/MgO
multilayers and demonstrate the potential for using them as a new model for
disordered superconductors. In this approach we control the annealing of the
MgB to yield an interesting new class of disordered (amorphous)
superconductors with relatively high transition temperatures. The multilayers
appear to exhibit quasi-two-dimensional superconductivity with controlled
anisotropy. We discuss the properties of the multilayers as the thickness of
the components of the bilayers vary.Comment: 7 pages, 8 figure
Understanding the nature of electronic effective mass in double-doped SrTiO
We present an approach to tune the effective mass in an oxide semiconductor
by a double doping mechanism. We demonstrate this in a model oxide system
SrLaTiO, where we can tune the effective mass ranging
from 6--20 as a function of filling or carrier concentration and
the scattering mechanism, which are dependent on the chosen lanthanum and
oxygen vacancy concentrations. The effective mass values were calculated from
the Boltzmann transport equation using the measured transport properties of
thin films of SrLaTiO. Our method, which shows that
the effective mass decreases with carrier concentration, provides a means for
understanding the nature of transport processes in oxides, which typically have
large effective mass and low electron mobility, contrary to the tradional high
mobility semiconductors.Comment: 5 pages with 4 figure
Reflection confocal nanoscopy using a super-oscillatory lens
A Superoscillatory lens (SOL) is known to produce a sub-diffraction hotspot
which is useful for high-resolution imaging. However, high-energy rings called
sidelobes coexist with the central hotspot. Additionally, SOLs have not yet
been directly used to image reflective objects due to low efficiency and poor
imaging properties. We propose a novel reflection confocal nanoscope which
mitigates these issues by relaying the SOL intensity pattern onto the object
and use conventional optics for detection. We experimentally demonstrate
super-resolution by imaging double bars with 330 nm separation using a 632.8 nm
excitation and a 0.95 NA objective. We also discuss the enhanced contrast
properties of the SOL nanoscope against a laser confocal microscope, and the
degradation of performance while imaging large objects.Comment: 17 pages, 15 figures, supplementary include
Determination of the spin-flip time in ferromagnetic SrRuO3 from time-resolved Kerr measurements
We report time-resolved Kerr effect measurements of magnetization dynamics in
ferromagnetic SrRuO3. We observe that the demagnetization time slows
substantially at temperatures within 15K of the Curie temperature, which is ~
150K. We analyze the data with a phenomenological model that relates the
demagnetization time to the spin flip time. In agreement with our observations
the model yields a demagnetization time that is inversely proportional to T-Tc.
We also make a direct comparison of the spin flip rate and the Gilbert damping
coefficient showing that their ratio very close to kBTc, indicating a common
origin for these phenomena
Critical thickness for itinerant ferromagnetism in ultrathin films of SrRuO
Ultrathin films of the itinerant ferromagnet SrRuO were studied using
transport and magnto-optic polar Kerr effect. We find that below 4 monolayers
the films become insulating and their magnetic character changes as they loose
their simple ferromagnetic behavior. We observe a strong reduction in the
magnetic moment which for 3 monolayers and below lies in the plane of the film.
Exchange-bias behavior is observed below the critical thickness, and may point
to induced antiferromagnetism in contact with ferromagnetic regions.Comment: 4 pages, 5 figure
Temperature Driven Structural Phase Transition in Tetragonal-Like BiFeO3
Highly-strained BiFeO3 exhibits a "tetragonal-like, monoclinic" crystal
structure found only in epitaxial films (with an out-of-plane lattice parameter
exceeding the in-plane value by >20%). Previous work has shown that this phase
is properly described as a M monoclinic structure at room temperature
[with a (010) symmetry plane, which contains the ferroelectric
polarization]. Here we show detailed temperature-dependent x-ray diffraction
data that evidence a structural phase transition at ~100C to a high-temperature
M phase ["tetragonal-like" but with a (1-10) symmetry plane].
These results indicate that the ferroelectric properties and domain structures
of strained BiFeO will be strongly temperature dependent.Comment: 10 pages, 3 figure
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