700 research outputs found
Direct Investigation of Superparamagnetism in Co Nanoparticle Films
A direct probe of superparamagnetism was used to determine the complete
anisotropy energy distribution of Co nanoparticle films. The films were
composed of self-assembled lattices of uniform Co nanoparticles 3 nm or 5 nm in
diameter, and a variable temperature scanning-SQUID microscope was used to
measure temperature-induced spontaneous magnetic noise in the samples. Accurate
measurements of anisotropy energy distributions of small volume samples will be
critical to magnetic optimization of nanoparticle devices and media.Comment: 4 pages, 4 figures. Submitted to Physical Review Letter
'STANDING WATCH IN KASSA' CITY WALLS AND WATCHTOWERS AND THEIR PHASES OF CONSTRUCTION
The Research Snippets are extracts from a monthly service called the Journal Article Summary Service. It is a service that summarises new articles in obstetrics and gynaecology published over the preceding month
Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO
The combination of ferromagnets with topological superconductors or
insulators allows for new phases of matter that support excitations such as
chiral edge modes and Majorana fermions. EuS, a wide-band-gap ferromagnetic
insulator with a Curie temperature around 16 K, and SrTiO (STO), an
important substrate for engineering heterostructures, may support these phases.
We present scanning superconducting quantum interference device (SQUID)
measurements of EuS grown epitaxially on STO that reveal micron-scale
variations in ferromagnetism and paramagnetism. These variations are oriented
along the STO crystal axes and only change their configuration upon thermal
cycling above the STO cubic-to-tetragonal structural transition temperature at
105 K, indicating that the observed magnetic features are due to coupling
between EuS and the STO tetragonal structure. We speculate that the STO
tetragonal distortions may strain the EuS, altering the magnetic anisotropy on
a micron-scale. This result demonstrates that local variation in the induced
magnetic order from EuS grown on STO needs to be considered when engineering
new phases of matter that require spatially homogeneous exchange
Macroscopic quantum tunneling and quasiparticle-tunneling blockade effect in s-wave/d-wave hybrid junctions
We have theoretically investigated macroscopic quantum tunneling (MQT) and
the influence of nodal quasiparticles and zero energy bound states (ZES) on MQT
in s-wave/ d-wave hybrid Josephson junctions. In contrast to d-wave/d-wave
junctions, the low-energy quasiparticle dissipation resulting from nodal
quasiparticles and ZES is suppressed due to a quasiparticle-tunneling blockade
effect in an isotropic s-wave superconductor. Therefore, the inherent
dissipation in these junctions is found to be very weak. We have also
investigated MQT in a realistic s-wave/d-wave (Nb/Au/YBCO) junction in which
Ohmic dissipation in a shunt resistance is stronger than the inherent
dissipation and find that MQT is observable within the current experimental
technology. This result suggests high potential of s-wave/d-wave hybrid
junctions for applications in quantum information devices.Comment: 4 pages, 3 figure
Phase-sensitive Evidence for d-wave Pairing Symmetry in Electron-doped Cuprate Superconductors
We present phase-sensitive evidence that the electron-doped cuprates
Nd1.85Ce0.15CuO4-y (NCCO) and Pr1.85Ce0.15CuO4-y (PCCO) have d-wave pairing
symmetry. This evidence was obtained by observing the half-flux quantum effect,
using a scanning SQUID microscope, in c-axis oriented films of NCCO or PCCO
epitaxially grown on tricrystal [100] SrTiO3 substrates designed to be
frustrated for a d(x2-y2) order parameter. Samples with two other
configurations, designed to b unfrustrated for a d-wave superconductor, do not
show the half-flux quantum effect.Comment: 4 pages, Latex, 4 figure
Induced paramagnetic states by localized -loops in grain boundaries
Recent experiments on high-temperature superconductors show paramagnetic
behavior localized at grain boundaries (GB). This paramagnetism can be
attributed to the presence unconventional d-wave induced -junctions. By
modeling the GB as an array of and conventional Josephson junction we
determine the conditions of the occurrence of the paramagnetic behavior.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Spontaneous Flux and Magnetic Interference Patterns in 0-pi Josephson Junctions
The spontaneous flux generation and magnetic field modulation of the critical
current in a 0-pi Josephson junction are calculated for different ratios of the
junction length to the Josephson penetration depth, and different ratios of the
0-junction length to the pi-junction length. These calculations apply to a
Pb-YBCO c-axis oriented junction with one YBCO twin boundary, as well as other
experimental systems. Measurements of such a junction can provide information
on the nature of the c-axis Josephson coupling and the symmetry of the order
parameter in YBCO. We find spontaneous flux even for very short symmetric 0-pi
junctions, but asymmetric junctions have qualitatively different behavior.Comment: 13 pages, TEX,+ 7 figures, postscrip
Condensation Energy and High Tc Superconductivity
From an analysis of the specific heat of one of the cuprate superconductors
it is shown, that even if a large part of the experimental specific heat
associated with the superconducting phase transition is due to fluctuations,
this part must be counted when one tries to extract the condensation energy
from the data. Previous work by Chakravarty, Kee and Abrahams, where the
fluctuation part was subtracted, has resulted in an incorrect estimation of the
condensation energy.Comment: 4 pages, 5 encapsulated Postscript figures, uses ReVTeX.st
Resolving the order parameter of High-T Superconductors through quantum pumping spectroscopy
The order parameter of High-T superconductors through a series of
experiments has been quite conclusively demonstrated to not be of the normal
type. It is either a pure -wave type or a mixture of
a with a small imaginary or
component. In this work a distinction is brought out among the four types,
i.e., , , and
types with the help of quantum pumping
spectroscopy. This involves a normal metal double barrier structure in contact
with a High-T superconductor. The pumped current, heat and noise show
different characteristics with change in order parameter revealing quite easily
the differences among these.Comment: 11 pages, 3 figures, 1 table, Manuscript revised with new material on
d+id' cas
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