1,472 research outputs found
Ferromagnet-superconductor proximity effect: The clean limit
We study theoretically the influence of ferromagnetic metals on a
superconducting film in the clean limit. Using a self-consistent solution of
the Bogoliubov--de Gennes equation for a ferromagnet-superconductor-ferromagnet
double junction we calculate the pair potential and conductance spectra as a
function of the superconducting layer thickness for different strengths of
ferromagnets and interface transparencies. We find that the pair potential and
the critical temperature are weakly perturbed by the exchange interaction and
do not drop to zero for any finite . On the other hand, for thin
superconducting films charge transport is spin polarized and exhibits a
significant dependence on the ferromagnetic strength and magnetization
alignment.Comment: 5 pages, 4 figure
Precision luminosity measurement at ILC
In these proceedings a novel approach to deal with the beam-induced effects
in luminosity measurement is presented. Based on the relativistic kinematics of
the collision frame of the Bhabha process, the beam-beam related uncertainties
can be reduced to the permille level independently of a precision with which
the beam parameters are known. Specific event selection combined with the
corrective methods we introduce, leads to the systematic uncertainty from the
beam-induced effects to be at a few permille level in the peak region above the
80% of the nominal centre-of-mass energies at ILC.Comment: Talk presented on behalf of the FCAL Collaboration at the
International Workshop on Future Linear Colliders (LCWS13) Tokyo, Japan,
11-15 November 201
Transmission Electron Study of Heteroepitaxial Growth in the BiSrCaCuO System
Films of BiSrCaCuO and BiSrCuO have been grown using Atomic-Layer-by-Layer Molecular Beam
Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been
combined with layers of closely-related metastable compounds like BiSrCaCuO (2278) and rare-earth-doped
compounds like BiSrDyCaCuO
(Dy:2212) to form heterostructures with unique superconducting properties,
including superconductor/insulator multilayers and tunnel junctions.
Transmission electron microscopy (TEM) has been used to study the morphology
and microstructure of these heterostructures. These TEM studies shed light on
the physical properties of the films, and give insight into the growth mode of
highly anisotropic solids like BiSrCaCuO.Comment: 17 pages, submitted to J. Materials Research. Email to
[email protected] if you want to receive copies of the figure
Josephson coupling through ferromagnetic heterojunctions with noncollinear magnetizations
We study the Josephson effect in clean heterojunctions that consist of
superconductors connected through two metallic ferromagnets with insulating
interfaces. We solve the scattering problem based on the Bogoliubov--de Gennes
equation for any relative orientation of in-plane magnetizations, arbitrary
transparency of interfaces, and mismatch of Fermi wave vectors. Both spin
singlet and triplet superconducting correlations are taken into account, and
the Josephson current is calculated as a function of the ferromagnetic layers
thicknesses and of the angle between their magnetizations. We find
that the critical Josephson current is a monotonic function of
when the junction is far enough from transitions. This holds when
ferromagnets are relatively weak. For stronger ferromagnets, variation of
induces switching between 0 and states and is
non-monotonic function, displaying characteristic dips at the transitions.
However, the non-monotonicity is the effect of a weaker influence of the
exchange potential in the case of non-parallel magnetizations. No substantial
impact of spin-triplet superconducting correlations on the Josephson current
has been found in the clean limit. Experimental control of the critical current
and transitions by varying the angle between magnetizations is
suggested.Comment: 7 pages, 8 figure
Plastic deformations in mechanically strained single-walled carbon nanotubes
Antiferromagnetic manipulation was used to controllably stretch individual metallic single-walled carbon nanotubes (SWNT's). We have found that SWNT's can sustain elongations as great as 30% without breaking. Scanned gate microscopy and transport measurements were used to probe the effects of the mechanical strain on the SWNT electronic properties, which revealed a strain-induced increase in intra-tube electronic scattering above a threshold strain of ~5–10 %. These findings are consistent with theoretical calculations predicting the onset of plastic deformation and defect formation in carbon nanotubes
Photoinduced melting of superconductivity in the high-Tc superconductor La2-xSrxCuO4 probed by time-resolved optical and THz techniques
Dynamics of depletion and recovery of superconducting state in La2-xSrxCuO_4
thin films is investigated utilizing optical pump-probe and optical pump - THz
probe techniques as a function of temperature and excitation fluence. The
absorbed energy density required to suppress superconductivity is found to be
about 8 times higher than the thermodynamically determined condensation energy
density and nearly temperature independent between 4 and 25 K. These findings
indicate that during the time when superconducting state suppression takes
place (~0.7 ps), a large part (nearly 90%) of the energy is transferred to the
phonons with energy lower than twice the maximum value of of the SC gap and
only 10% is spent on Cooper pair breaking.Comment: 8 pages, 5 figure
Spin excitations in a single LaCuO layer
The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart
of the mystery of the cuprates
\cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}.
In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling
stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system
however, thermal spin fluctuations melt long range order at any finite
temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer
magnetic spectral weight out of a well-defined magnon excitation into a
magnetic continuum, the nature of which remains controversial
\cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the
spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show
that coherent magnons persist even in a single layer of \LCO{} despite the loss
of magnetic order, with no evidence for resonating valence bond (RVB)-like spin
correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these
excitations are well described by linear spin wave theory (LSWT). We also
observe a high-energy magnetic continuum in the isotropic magnetic response.
This high-energy continuum is not well described by 2 magnon LSWT, or indeed
any existing theories.Comment: Revised version to appear in Nature Materials; 6 pages,4 figure
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