2,256 research outputs found
Single Impurity Effects in Multiband Superconductors with Different Sign Order Parameters
A single impurity problem is investigated for multiband s-wave
superconductors with different sign order parameters (+-s-wave superconductors)
suggested in Fe-pnictide superconductors. Not only intraband but also interband
scattering is considered at the impurity. The latter gives rise to
impurity-induced local boundstates close to the impurity. We present an exact
form of the energy of the local boundstates as a function of strength of the
two types of impurity scattering. The essential role of the impurity is
unchanged in finite number of impurities. The main conclusions for a single
impurity problem help us understand effects of dense impurities in the +-s-wave
superconductors. Local density of states around the single impurity is also
investigated. We suggest impurity site nuclear magnetic resonance as a suitable
experiment to probe the local boundstates that is peculiar to the +-s-wave
state. We find that the +-s-wave model is mapped to a chiral dx2-y2+-idxy-wave,
reflecting the unconventional nature of the sign reversing order parameter. For
a quantum magnetic impurity, interband scattering destabilizes the Kondo
singlet.Comment: 23 pages, 7 figures, to be published in J. Phys. Soc. Jpn. (2009) No.
Projectile fragmentation reactions and production of nuclei near the neutron drip-line
The reaction mechanism of projectile fragmentation at intermediate energies
has been investigated observing the target dependence of the production cross
sections of very neutron-rich nuclei. Measurement of longitudinal momentum
distributions of projectile-like fragments within a wide range of fragment mass
and its charge was performed using a hundred-MeV/n Ar beam incident on
Be and Ta targets. By measurement of fragment momentum distribution, a
parabolic mass dependence of momentum peak shift was observed in the results of
both targets, and a phenomenon of light-fragment acceleration was found only in
the Be-target data. The analysis of production cross sections revealed an
obvious enhancement of the target dependence except target size effect when the
neutron excess is increased. This result implies the breakdown of factorization
(BOF) of production cross sections for very neutron-rich nuclei near the drip
line.Comment: 16 pages, 18 figures, submitted to Phys. Rev.
Spin dependent scattering of a domain-wall of controlled size
Magnetoresistance measurements in the CPP geometry have been performed on
single electrodeposited Co nanowires exchange biased on one side by a sputtered
amorphous GdCo layer. This geometry allows the stabilization of a single domain
wall in the Co wire, the thickness of which can be controlled by an external
magnetic field. Comparing magnetization, resistivity, and magnetoresistance
studies of single Co nanowires, of GdCo layers, and of the coupled system,
gives evidence for an additional contribution to the magnetoresistance when the
domain wall is compressed by a magnetic field. This contribution is interpreted
as the spin dependent scattering within the domain wall when the wall thickness
becomes smaller than the spin diffusion length.Comment: 9 pages, 13 figure
Current patterns and magnetic impurities in time-reversal breaking superconductor
We study the impurity effect in the time reversal symmetry ()
breaking superconductor based on the Bogoliubov-de Gennes (BdG) equations. In
-violating superconductors, spontaneous currents are induced around
the impurity. The current patterns around the impurity reflect the structures
of the Cooper pairs. We investigate impurity problem numerically for two kinds
of violating superconductors and and investigate the currents around the impurity. We also study the
effects of the magnetic impurity in p-wave ()
superconductor, especially in view of the zero-energy crossing of energy levels
related to the phase transition of the ground state.Comment: 18 page
Assessment of active dopants and p-n junction abruptness using in-situ biased 4D-STEM
A key issue in the development of high-performance semiconductor devices is
the ability to properly measure active dopants at the nanometer scale. 4D
scanning transmission electron microscopy and off-axis electron holography have
opened up the possibility of studying the electrostatic properties of a p-n
junction with nm-scale spatial resolution. The complete description of a p-n
junction must take into account the precise evolution of the concentration of
dopants around the junction, since the sharpness of the dopant transition
directly influences the built-in potential and the maximum electric field.
Here, a contacted silicon p-n junction is studied through in-situ biased
4D-STEM. Measurements of electric field, built-in voltage, depletion region
width and charge density in the space charge region are combined with
analytical equations as well as finite-element simulations in order to evaluate
the quality of the junction interface. The nominally-symmetric, highly doped
() junction presents an electric
field and built-in voltage much lower than expected for an abrupt junction.
These experimental results are consistent with electron holography data. All
measured junction parameters are compatible with the presence of an
intermediate region with a graded profile of the dopants at the p-n interface.
This hypothesis is also consistent with the evolution of the electric field
with bias. These results demonstrate that in-situ biased 4D-STEM enables a
better understanding of the electrical properties of semiconductor p-n
junctions with nm-scale resolution.Comment: 13 pages, 5 figure
Effect of spin-orbit impurity scattering in the superconducting state of t-J model
We study the effect of magnetic impurities in the d_{x^2-y^2}-wave
superconducting (SC) state of the two dimensional t-J model.The spin-orbit and
the spin-exchange interactions are examined by treating the impurity as a
classical spin. The Bogoliubov de Gennes equation derived within a slave-boson
mean-field approximation is solved numerically at T = 0. The spin-exchange
scattering induces spin-triplet p-wave SC order parameters near the impurity,
while a SC state with broken time-reversal symmetry and a spontaneous current
appears in the presence of the spin-orbit interaction. When both interactions
coexist, it turns out that a state which carries a spontaneous spin current
occurs.Comment: 4 pages, 7 figure
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