232 research outputs found
In-situ growth of superconducting NdFeAs(O,F) thin films by Molecular Beam Epitaxy
The recently discovered high temperature superconductor F-doped LaFeAsO and
related compounds represent a new class of superconductors with the highest
transition temperature (Tc) apart from the cuprates. The studies ongoing
worldwide are revealing that these Fe-based superconductors are forming a
unique class of materials that are interesting from the viewpoint of
applications. To exploit the high potential of the Fe-based superconductors for
device applications, it is indispensable to establish a process that enables
the growth of high quality thin films. Efforts of thin film preparation started
soon after the discovery of Fe-based superconductors, but none of the earlier
attempts had succeeded in an in-situ growth of a superconducting film of
LnFeAs(O,F) (Ln=lanthanide), which exhibits the highest Tc to date among the
Fe-based superconductors. Here, we report on the successful growth of
NdFeAs(O,F) thin films on GaAs substrates, which showed well-defined
superconducting transitions up to 48 K without the need of an ex-situ heat
treatment
Noise-free scattering of the quantized electromagnetic field from a dispersive linear dielectric
We study the scattering of the quantized electromagnetic field from a linear,
dispersive dielectric using the scattering formalism for quantum fields. The
medium is modeled as a collection of harmonic oscillators with a number of
distinct resonance frequencies. This model corresponds to the Sellmeir
expansion, which is widely used to describe experimental data for real
dispersive media. The integral equation for the interpolating field in terms of
the in field is solved and the solution used to find the out field. The
relation between the in and out creation and annihilation operators is found
which allows one to calculate the S-matrix for this system. In this model, we
find that there are absorption bands, but the input-output relations are
completely unitary. No additional quantum noise terms are required.Comment: Revtex, submitted to Physical Review
Growth of a smooth CaF 2 layer on NdFeAsO thin film
We studied the method to grow a smooth and flat CaF 2 layer on NdFeAsO thin films since CaF 2 is a promising candidate material for the barrier layer of a superconducting junction. When the CaF 2 layer was grown at 800°C, the surface was very rough because {111} facets had grown preferentially. However, when CaF 2 was grown at lower temperatures and post-annealed in situ at 800°C for 30 min the facets were eliminated and a CaF 2 layer with a smooth surface was obtained. Fluorine diffusing from CaF 2 into NdFeAsO was observed when CaF 2 was grown at high temperatures, but the diffusion was suppressed by lowering the growth temperature to 400°C
Nonlinear eigenvalue problem for optimal resonances in optical cavities
The paper is devoted to optimization of resonances in a 1-D open optical
cavity. The cavity's structure is represented by its dielectric permittivity
function e(s). It is assumed that e(s) takes values in the range 1 <= e_1 <=
e(s) <= e_2. The problem is to design, for a given (real) frequency, a cavity
having a resonance with the minimal possible decay rate. Restricting ourselves
to resonances of a given frequency, we define cavities and resonant modes with
locally extremal decay rate, and then study their properties. We show that such
locally extremal cavities are 1-D photonic crystals consisting of alternating
layers of two materials with extreme allowed dielectric permittivities e_1 and
e_2. To find thicknesses of these layers, a nonlinear eigenvalue problem for
locally extremal resonant modes is derived. It occurs that coordinates of
interface planes between the layers can be expressed via arg-function of
corresponding modes. As a result, the question of minimization of the decay
rate is reduced to a four-dimensional problem of finding the zeroes of a
function of two variables.Comment: 16 page
Input-Output Relations in Optical Cavities: a Simple Point of View
In this work we present a very simple approach to input-output relations in
optical cavities, limiting ourselves to one- and two-photon states of the
field.
After field quantization, we derive the non-unitary transformation between
{\em Inside} and {\em Outside} annihilation and creation operators. Then we
express the most general two-photon state generated by {\em Inside} creation
operators, through base states generated by {\em Outside} creation operators.
After renormalization of coefficients of inside two-photon state, we calculate
the outside photon-number probability distribution in a general case. Finally
we treat with some detail the single mode and symmetrical cavity case.Comment: 34 pages, 5 figures jpg, LaTe
Analysis of interdiffusion between SmFeAsO0.92F0.08 and metals for ex situ fabrication of superconducting wire
We demonstrate the fabrication of superconducting SmFeAsO1-xFx (Sm-1111)
wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a
binder composed of SmF3, samarium arsenide, and iron arsenide were used to
synthesize the superconducting core. Although the F content of Sm-1111 is
reduced in the process of ex-situ fabrication, the binder compensates by
sufficiently supplementing the F content, thereby preventing a decrease in the
superconducting transition temperature and a shrinking of the superconducting
volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the
transport critical current density reaches the highest value of ~4000 A/cm2 at
4.2 K
DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2 epitaxial films
DC superconducting quantum interference devices (dc-SQUIDs) were fabricated
in Co-doped BaFe2As2 epitaxial films on (La, Sr)(Al, Ta)O3 bicrystal substrates
with 30deg misorientation angles. The 18 x 8 micro-meter^2 SQUID loop with an
estimated inductance of 13 pH contained two 3 micro-meter wide grain boundary
junctions. The voltage-flux characteristics clearly exhibited periodic
modulations with deltaV = 1.4 micro-volt at 14 K, while the intrinsic flux
noise of dc-SQUIDs was 7.8 x 10^-5 fai0/Hz^1/2 above 20 Hz. The rather high
flux noise is mainly attributed to the small voltage modulation depth which
results from the superconductor-normal metal-superconductor junction nature of
the bicrystal grain boundary
A collaborative approach to combining service, teaching, and research
Objective. To describe a faculty-student collaborative model and its outcomes on teaching, service, and scholarship.
Design. A Medicare Part D elective course was offered that consisted of classroom and experiential learning where pharmacy students participated in community outreach events to assist Medicare beneficiaries with Part D plan selection. The course training was expanded to include medication therapy management (MTM) and the administration of immunizations. At the completion of the course, students collaborated with faculty members on research endeavors.
Evaluation. During the first 6 years of this course, the class size more than doubled from 20 to 42 students, and all students participating in the course met the IPPE requirements for community outreach. Over that same period, the number of beneficiaries receiving assistance with their Part D plan grew from 72 to 610; and with the help of students starting in 2011, faculty members had 28 poster presentations at national conferences, 7 invited podium presentations at national/international meetings, and published 8 manuscripts in peer-reviewed journals.
Conclusion. Through collaborative efforts, this model took an elective course and provided classroom and experiential learning for students, needed health services for the community, and opportunities to pursue wide ranging research projects for faculty members and students
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