21,447 research outputs found

### Detection of local-moment formation using the resonant interaction between coupled quantum wires

We study the influence of many-body interactions on the transport
characteristics of a novel device structure, consisting of a pair of quantum
wires that are coupled to each other by means of a quantum dot. Under
conditions where a local magnetic moment is formed in one of the wires, we show
that tunnel coupling to the other gives rise to an associated peak in its
density of states, which can be detected directly in a conductance measurement.
Our theory is therefore able to account for the key observations in the recent
study of T. Morimoto et al. [Appl. Phys. Lett. {\bf 82}, 3952 (2003)], and
demonstrates that coupled quantum wires may be used as a system for the
detection of local magnetic-moment formation

### Transverse Ward-Takahashi Identity, Anomaly and Schwinger-Dyson Equation

Based on the path integral formalism, we rederive and extend the transverse
Ward-Takahashi identities (which were first derived by Yasushi Takahashi) for
the vector and the axial vector currents and simultaneously discuss the
possible anomaly for them. Subsequently, we propose a new scheme for writing
down and solving the Schwinger-Dyson equation in which the the transverse
Ward-Takahashi identity together with the usual (longitudinal) Ward-Takahashi
identity are applied to specify the fermion-boson vertex function. Especially,
in two dimensional Abelian gauge theory, we show that this scheme leads to the
exact and closed Schwinger-Dyson equation for the fermion propagator in the
chiral limit (when the bare fermion mass is zero) and that the Schwinger-Dyson
equation can be exactly solved.Comment: 22 pages, latex, no figure

### Detection of spin voltaic effect in a p-n heterojunction

Model calculation and experimental data of
circularly-polarized-light-dependent photocurrent in a n-AlGaAs/p-InGaAs/p-GaAs
heterostructure are reported. It is found that, under the appropriate forward
bias condition, spin voltaic effect (SVE) can survive across the heterojunction
and give rise to detectable polarization-dependent photocurrent signals which
are greater than the signals due to the magnetic circular dichroism. Our
analysis suggests that SVE can be enhanced by optimization of layer thickness,
doping profile, and applied bias, making SVE favorable for the realization of a
semiconductor-based polarization detector, a spin-photodiode (spin-PD).Comment: 16 pages, 3figure

### Role of surface states in STM spectroscopy of (111) metal surfaces with Kondo adsorbates

A nearly-free-electron (NFE) model to describe STM spectroscopy of (111)
metal surfaces with Kondo impurities is presented. Surface states are found to
play an important role giving a larger contribution to the conductance in the
case of Cu(111) and Au(111) than Ag(111) surfaces. This difference arises from
the farther extension of the Ag(111) surface state into the substrate. The
different line shapes observed when Co is adsorbed on different substrates can
be explained from the position of the surface band onset relative to the Fermi
energy. The lateral dependence of the line shape amplitude is found to be
bulk-like for R|| < 4 Amstrongs and surface-like at larger distances, in
agreement with experimental data.Comment: 4 pages, 3 eps figure

### Realization of Strong Coupling Fixed Point in Multilevel Kondo Models

Impurity four- and six-level Kondo model, in which an ion is tunneling among
four- and six-stable points and interacting with surrounding conduction
electrons, are investigated by using the perturbative and numerical
renormalization group methods. It is shown that purely orbital Kondo effects
occur at low temperatures in these systems which are direct generalizations of
the Kondo effect in the so-called two-level system. This result offers a good
explanation for the enhanced and magnetically robust Sommerfeld coefficient
observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published
in Journal of Physical Society Japan supplemen

### Electrical measurements on fused quartz under shock compression

The resistivities of specimens of SiO_2 (fused quartz) singly and doubly shocked in the 10–45 and 27–90 GPa ranges, respectively, demonstrate a marked decrease from values of ∼10–0.1 Ω⋅m at a single‐shock pressure of ∼40 and a double‐shock pressure of ∼74 GPa. These states correspond to calculated shock temperatures of ∼3300 and ∼3600 K, respectively. At shock pressures below 36 GPa the measured resistivity versus calculated shock temperature agrees closely with ambient‐pressure and high‐temperature resistivity data. This suggests that the ionic conduction mechanisms inferred to control electrical properties at ambient pressure also act under shock‐induced high temperatures in quartz and the presumed high‐pressure phase, stishovite into which fused quartz appears to transform above 20 GPa. At 36–40 GPa the rapid decrease in resistivity by a factor of 10^2 suggests a further transformation to an unknown phase which may correspond to the onset of melting. The existing pressure‐density Hugoniot data do not demonstrate any anomalous density change associated with this phase change

### Shock-induced radiation spectra of fused quartz

An optical multichannel analyzer is applied to observe shock-induced radiation spectra of fused quartz in the 23–31 GPa shock-pressure range. Characteristics of sample-driver interface strongly influence both intensity and profile of the observed spectra. Brightness and color temperature are determined by an integration of spectral radiance and a fit to the greybody radiation spectrum, respectively. The resultant brightness and color temperature are lower and considerably higher than those estimated by the theoretical calculation, respectively. Some broad but strong line spectra are, however, superimposed onto the continuous greybody radiation spectrum even though the influences of the interface are reduced as much as possible. The line spectra are probably caused by electroluminescence and/or triboluminescence

### Prediction of the capacitance lineshape in two-channel quantum dots

We propose a set-up to realize two-channel Kondo physics using quantum dots.
We discuss how the charge fluctuations on a small dot can be accessed by using
a system of two single electron transistors arranged in parallel. We derive a
microscopic Hamiltonian description of the set-up that allows us to make
connection with the two-channel Anderson model (of extended use in the context
of heavy-Fermion systems) and in turn make detailed predictions for the
differential capacitance of the dot. We find that its lineshape, which we
determined precisely, shows a robust behavior that should be experimentally
verifiable.Comment: 4 pages, 3 figure

### Future of Ultraviolet Astronomy Based on Six Years of IUE Research

Physical insights into the various astronomical objects which were studied using the International Ultraviolet Explorer (IUE) satellite. Topics covered included galaxies, cool stars, hot stars, close binaries, variable stars, the interstellar medium, the solar system, and IUE follow-on missions

### Theory of Orbital Kondo Effect with Assisted Hopping in Strongly Correlated Electron Systems: Parquet Equations, Superconductivity and Mass Enhancement

Orbital Kondo effect is treated in a model, where additional to the
conduction band there are localized orbitals close to the Fermi energy. If the
hopping between the conduction band and the localized heavy orbitals depends on
the occupation of the atomic orbitals in the conduction band then orbital Kondo
correlation occurs. The noncommutative nature of the coupling required for the
Kondo effect is formally due to the form factors associated with the assisted
hopping which in the momentum representation depends on the momenta of the
conduction electrons involved. The leading logarithmic vertex corrections are
due to the local Coulomb interaction between the electrons on the heavy orbital
and in the conduction band. The renormalized vertex functions are obtained as a
solution of a closed set of differential equations and they show power
behavior. The amplitude of large renormalization is determined by an infrared
cutoff due to finite energy and dispersion of the heavy particles. The enhanced
assisted hopping rate results in mass enhancement and attractive interaction in
the conduction band. The superconductivity transition temperature calculated is
largest for intermediate mass enhancement, $m^*/m \approx 2-3$. For larger mass
enhancement the small one particle weight ($Z$) in the Green's function reduces
the transition temperature which may be characteristic for otherComment: 32 pages, RevTeX 3.0, figures on reques

- …