1,011 research outputs found
Comment on ``Local dimer-adatom stacking fault structures from 3x3 to 13x13 along Si(111)-7x7 domain boundaries''
Zhao et al. [Phys.Rev.B 58, 13824 (1998)] depicted several atomic structures
of domain boundaries on a Si(111) surface and criticized the article by the
present author and the co-workers. I will point out that their criticism is
incorrect and their structure models have no consistency.Comment: 2 pages. Physical Review B, to appea
Notes on S-Matrix of Non-critical N=2 String
In this paper we discuss the scattering S-matrix of non-critical N=2 string
at tree level. First we consider the \hat{c}<1 string defined by combining the
N=2 time-like linear dilaton SCFT with the N=2 Liouville theory. We compute
three particle scattering amplitudes explicitly and find that they are actually
vanishing. We also find an evidence that this is true for higher amplitudes.
Next we analyze another \hat{c}<1 string obtained from the N=2 time-like
Liouville theory, which is closely related to the N=2 minimal string. In this
case, we find a non-trivial expression for the three point functions. When we
consider only chiral primaries, the amplitudes are very similar to those in the
(1,n) non-critical bosonic string.Comment: 27 pages, harvmac, section 5 modified: a relation to (1,n)
non-critical bosonic string adde
Closed Bosonic String Partition Function in Time Independent Exact PP-Wave Background
The modular invariance of the one-loop partition function of the closed
bosonic string in four dimensions in the presence of certain homogeneous exact
pp-wave backgrounds is studied. In the absence of an axion field the partition
function is found to be modular invariant. In the presence of an axion field
modular invariace is broken. This can be attributed to the light-cone gauge
which breaks the symmetry in the -, -directions. Recovery of this
broken modular invariance suggests the introduction of twists in the
world-sheet directions. However, one needs to go beyond the light-cone gauge to
introduce such twists.Comment: 17 pages, added reference
Out-of-plane dielectric constant and insulator-superconductor transition in Bi_2Sr_2Dy_{1-x}Er_xCu_2O_8 single crystals
The out-of-plane dielectric constant of the parent insulator of the
high-temperature superconductor Bi_2Sr_2(Dy,Er)Cu_2O_8 was measured and
analysed from 80 to 300 K in the frequency range of 10^6-10^9 Hz. All the
samples were found to show a fairly large value of 10-60, implying some kind of
charge inhomogeneity in the CuO_2 plane. Considering that the superconducting
sample Bi_2Sr_2(Ca,Pr)Cu_2O_8 also shows a similar dielectric constant, the
charge inhomogeneity plays an important role in the insulator-superconductor
transition.Comment: RevTex4 format, 5 pages, 3 figures, submitted to J. Phys. Condens.
Ma
Solitons and excitations in the duality-based matrix model
We analyse a specific, duality-based generalization of the hermitean matrix
model. The existence of two collective fields enables us to describe specific
excitations of the hermitean matrix model. By using these two fields, we
construct topologically non-trivial solutions (BPS solitons) of the model. We
find the low-energy spectrum of quantum fluctuations around the uniform
solution. Furthermore, we construct the wave functional of the ground state and
obtain the corresponding Green function.Comment: 13 pages,v2: new solutions constructed, title changed accordingl
Non-local Control of the Kondo Effect in a Double Quantum Dot-Quantum Wire Coupled System
We have performed low-temperature transport measurements on a double quantum
dot-quantum wire coupled device and demonstrated non-local control of the Kondo
effect in one dot by manipulating the electronic spin states of the other. We
discuss the modulation of the local density of states in the wire region due to
the Fano-Kondo antiresonance, and the Ruderman-Kittel-Kasuya-Yoshida (RKKY)
exchange interaction as the mechanisms responsible for the observed features.Comment: 4 pages, 4 figure
A Cooper pair light emitting diode
We demonstrate Cooper-pair's drastic enhancement effect on band-to-band
radiative recombination in a semiconductor. Electron Cooper pairs injected from
a superconducting electrode into an active layer by the proximity effect
recombine with holes injected from a p-type electrode and dramatically
accelerate the photon generation rates of a light emitting diode in the
optical-fiber communication band. Cooper pairs are the condensation of
electrons at a spin-singlet quantum state and this condensation leads to the
observed enhancement of the electric-dipole transitions. Our results indicate
the possibility to open up new interdisciplinary fields between
superconductivity and optoelectronics.Comment: 5 pages (4 figures
Andreev magnetotransport in low-dimensional proximity structures: Spin-dependent conductance enhancement
We study the excess conductance due to the superconducting proximity effect
in a ballistic two-dimensional electron system subject to an in-plane magnetic
field. We show that under certain conditions the interplay of the Zeeman spin
splitting and the effect of a screening supercurrent gives rise to a
spin-selective Andreev enhancement of the conductance and anomalies in its
voltage, temperature and magnetic field characteristics. The magnetic-field
influence on Andreev reflection is discussed in the context of using
superconducting hybrid junctions for spin detection.Comment: 4 pages, 5 figure
Effects of Magnetic Field on Josephson Current in SNS System
The effect of a magnetic field on Josephson current has been studied for a
superconductor/normal-metal/superconductor (SNS) system, where N is a
two-dimensional electron gas in a confining potential. It is found that the
dependence of Josephson currents on the magnetic field are sensitive to the
width of the normal metal. If the normal metal is wide and contains many
channels (subbands), the current on a weak magnetic field shows a dependence
similar to a Fraunhofer-pattern in SIS system and, as the field gets strong, it
shows another type of oscillatory dependence on the field resulting from the
Aharonov-Bohm interference between the edge states. As the number of channels
decreases (i.e. normal metal gets narrower), however, the dependence in the
region of the weak field deviates from a clear Fraunhofer pattern and the
amplitude of the oscillatory dependence in the region of the strong field is
reduced.Comment: 14 pages, 9 figure
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