379 research outputs found
Theory of Asymmetric Tunneling in the cuprate superconductors
We explain quantitatively, within the Gutzwiller-Resonating Valence Bond
theory, the puzzling observation of tunneling conductivity between a metallic
point and a cuprate high- superconductor which is markedly asymmetric
between positive and negative voltage biases. The asymmetric part does not have
a "coherence peak" but does show structure due to the gap. The fit to data is
satisfactory within the over-simplifications of the theory; in particular, it
explains the marked "peak-dip-hump" structure observed on the hole side and a
number of other qualitative observations. This asymmetry is strong evidence for
the projective nature of the ground state and hence for "t-J" physics.Comment: 5 pages, 3 figures, revised 6/1/0
Flux Creep and Flux Jumping
We consider the flux jump instability of the Bean's critical state arising in
the flux creep regime in type-II superconductors. We find the flux jump field,
, that determines the superconducting state stability criterion. We
calculate the dependence of on the external magnetic field ramp rate,
. We demonstrate that under the conditions typical for most of the
magnetization experiments the slope of the current-voltage curve in the flux
creep regime determines the stability of the Bean's critical state, {\it i.e.},
the value of . We show that a flux jump can be preceded by the
magneto-thermal oscillations and find the frequency of these oscillations as a
function of .Comment: 7 pages, ReVTeX, 2 figures attached as postscript file
Josephson Current in the Presence of a Precessing Spin
The Josephson current in the presence of a precessing spin between various
types of superconductors is studied. It is shown that the Josephson current
flowing between two spin-singlet pairing superconductors is not modulated by
the precession of the spin. When both superconductors have equal-spin-triplet
pairing state, the flowing Josephson current is modulated with twice of the
Larmor frequency by the precessing spin. It was also found that up to the
second tunneling matrix elements, no Josephson current can occur with only a
direct exchange interaction between the localized spin and the conduction
electrons, if the two superconductors have different spin-parity pairing
states.Comment: 5 pages, 1 figur
Output state in multiple entanglement swapping
The technique of quantum repeaters is a promising candidate for sending
quantum states over long distances through a lossy channel. The usual
discussions of this technique deals with only a finite dimensional Hilbert
space. However the qubits with which one implements this procedure will "ride"
on continuous degrees of freedom of the carrier particles. Here we analyze the
action of quantum repeaters using a model based on pulsed parametric down
conversion entanglement swapping. Our model contains some basic traits of a
real experiment. We show that the state created, after the use of any number of
parametric down converters in a series of entanglement swappings, is always an
entangled (actually distillable) state, although of a different form than the
one that is usually assumed. Furthermore, the output state always violates a
Bell inequality.Comment: 11 pages, 6 figures, RevTeX
Electronic structure study of double perovskites FeReO (A=Ba,Sr,Ca) and SrMoO (M=Cr,Mn,Fe,Co) by LSDA and LSDA+U
We have implemented a systematic LSDA and LSDA+U study of the double
perovskites FeReO (A=Ba,Sr,Ca) and SrMoO
(M=Cr,Mn,Fe,Co) for understanding of their intriguing electronic and magnetic
properties. The results suggest a ferrimagnetic (FiM) and half-metallic (HM)
state of FeReO (A=Ba,Sr) due to a pdd- coupling between the
down-spin Re/Fe orbitals via the intermediate O
ones, also a very similar FiM and HM state of SrFeMoO.
In contrast, a decreasing Fe component at Fermi level () in the
distorted CaFeReO partly accounts for its nonmetallic behavior,
while a finite - coupling between the down-spin
Re/Fe orbitals being present at serves to
stabilize its FiM state. For SrCrMoO compared with
SrFeMoO, the coupling between the down-spin Mo/Cr
orbitals decreases as a noticeable shift up of the Cr 3d
levels, which is likely responsible for the decreasing value and weak
conductivity. Moreover, the calculated level distributions indicate a
Mn(Co)/Mo ionic state in SrMnMoO
(SrCoMoO), in terms of which their antiferromagnetic insulating
ground state can be interpreted. While orbital population analyses show that
owing to strong intrinsic pd covalence effects, SrMoO
(M=Cr,Mn,Fe,Co) have nearly the same valence state combinations, as accounts
for the similar M-independent spectral features observed in them.Comment: 21 pages, 3 figures. to be published in Phys. Rev. B on 15th Se
Big, Fast Vortices in the d-RVB theory of High Temperature Superconductivity
The effect of proximity to a Mott insulating phase on the superflow
properties of a d-wave superconductor is studied using the slave boson-U(1)
gauge theory model. The model has two limits corresponding to superconductivity
emerging either out of a 'renormalized fermi liquid' or out of a
non-fermi-liquid regime. Three crucial physical parameters are identified: the
size of the vortex \textit{as determined from the supercurrent it induces;} the
coupling of the superflow to the quasiparticles and the 'nondissipative time
derivative' term. As the Mott phase is approached, the core size as defined
from the supercurrent diverges, the coupling between superflow and
quasiparticles vanishes, and the magnitude of the nondissipative time
derivative dramatically increases. The dissipation due to a moving vortex is
found to vary as the third power of the doping. The upper critical field and
the size of the critical regime in which paraconductivity may be observed are
estimated, and found to be controlled by the supercurrent length scale
Impurity and interface bound states in and superconductors
Motivated by recent discoveries of novel superconductors such as
NaCoOHO and SrRuO, we analysize features of
quasi-particle scattering due to impurities and interfaces for possible gapful
and Cooper pairing. A bound state appears near
a local impurity, and a band of bound states form near an interface. We
obtained analytically the bound state energy, and calculated the space and
energy dependent local density of states resolvable by high-resolution scanning
tunnelling microscopy. For comparison we also sketch results of impurity and
surface states if the pairing is nodal p- or d-wave.Comment: 4 pages, 4 figure
Tardbpl splicing rescues motor neuron and axonal development in a mutant tardbp zebrafish
Mutations in the transactive response DNA binding protein-43 (TARDBP/TDP-43) gene, which regulates transcription and splicing, causes a familial form of amyotrophic lateral sclerosis (ALS). Here, we characterize and report the first tardbp mutation in zebrafish, which introduces a premature stop codon (Y220X), eliminating expression of the Tardbp protein. Another TARDBP ortholog, tardbpl, in zebrafish is shown to encode a Tardbp-like protein which is truncated compared with Tardbp itself and lacks part of the C-terminal glycine-rich domain (GRD). Here, we show that tardbp mutation leads to the generation of a novel tardbpl splice form (tardbpl-FL) capable of making a full-length Tardbp protein (Tardbpl-FL), which compensates for the loss of Tardbp. This finding provides a novel in vivo model to study TDP-43-mediated splicing regulation. Additionally, we show that elimination of both zebrafish TARDBP orthologs results in a severe motor phenotype with shortened motor axons, locomotion defects and death at around 10 days post fertilization. The Tardbp/Tardbpl knockout model generated in this study provides an excellent in vivo system to study the role of the functional loss of Tardbp and its involvement in ALS pathogenesis
A Two-Step Quantum Direct Communication Protocol Using Einstein-Podolsky-Rosen Pair Block
A protocol for quantum secure direct communication using blocks of EPR pairs
is proposed. A set of ordered EPR pairs is used as a data block for sending
secret message directly. The ordered EPR set is divided into two particle
sequences, a checking sequence and a message-coding sequence. After
transmitting the checking sequence, the two parties of communication check
eavesdropping by measuring a fraction of particles randomly chosen, with random
choice of two sets of measuring bases. After insuring the security of the
quantum channel, the sender, Alice encodes the secret message directly on the
message-coding sequence and send them to Bob. By combining the checking and
message-coding sequences together, Bob is able to read out the encoded messages
directly. The scheme is secure because an eavesdropper cannot get both
sequences simultaneously. We also discuss issues in a noisy channel.Comment: 8 pages and 2 figures. To appear in Phys Rev
Quantum error rejection code with spontaneous parametric conversion
We propose a linear optics scheme with SPDC process to test the fault
tolerance property of quantum error correction code. To transmit an unknown
qubit robustly through the noisy channel, one may first encode it into a
certain quantum error correction code and then transmit it. The remote party
decodes it and stores it. Sending a qubit in such a way can significantly
reduces the error rate compared with directly sending the qubit itself. Here we
show how to realize such a scheme by linear optics.Comment: To appear in Phys. Rev. A. 18 pages, 2 figure, minor erros corrected
and more explanations added to increase the readabilit
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