1,393 research outputs found
Quantitative Analysis of Hydrogenated DLC Films by Visible Raman Spectroscopy
The correlations between properties of hydrogenated diamond like carbon films
and their Raman spectra have been investigated. The films are prepared by
plasma deposition technique, keeping different hydrogen to methane ratio during
the growth process. The hydrogen concentration, sp content, hardness and
optical Tauc gap of the materials have been estimated from a detail analysis of
their Raman spectra. We have also measured the same parameters of the films by
using other commonly used techniques, like sp content in films by x-ray
photoelectron spectroscopy, their Tauc gap by ellipsometric measurements and
hardness by micro-hardness testing. The reasons for the mismatch between the
characteristics of the films, as obtained by Raman measurements and by the
above mentioned techniques, have been discussed. We emphasize on the importance
of the visible Raman spectroscopy in reliably predicting the above key
properties of DLC films.Comment: 19 pages, 8 figure
Probing the spin states of three interacting electrons in quantum dots
We observe a low-lying sharp spin mode of three interacting electrons in an
array of nanofabricated AlGaAs/GaAs quantum dots by means of resonant inelastic
light scattering. The finding is enabled by a suppression of the inhomogeneous
contribution to the excitation spectra obtained by reducing the number of
optically-probed quantum dots. Supported by configuration-interaction
calculations we argue that the observed spin mode offers a direct probe of
Stoner ferromagnetism in the simplest case of three interacting spin one-half
fermions
Delocalized-localized transition in a semiconductor two-dimensional honeycomb lattice
We report the magneto-transport properties of a two-dimensional electron gas
in a modulation-doped AlGaAs/GaAs heterostructure subjected to a lateral
potential with honeycomb geometry. Periodic oscillations of the
magneto-resistance and a delocalized-localized transition are shown by applying
a gate voltage. We argue that electrons in such artificial-graphene lattices
offer a promising approach for the simulation of quantum phases dictated by
Coulomb interactions
Mesoscopic Superconducting Disc with Short-Range Columnar Defects
Short-range columnar defects essentially influence the magnetic properties of
a mesoscopic superconducting disc.They help the penetration of vortices into
the sample, thereby decrease the sample magnetization and reduce the upper
critical field. Even the presence of weak defects split a giant vortex state
(usually appearing in a clean disc in the vicinity of the transition to a
normal state) into a number of vortices with smaller topological charges. In a
disc with a sufficient number of strong enough defects vortices are always
placed onto defects. The presence of defects lead to the appearance of
additional magnetization jumps related to the redistribution of vortices which
are already present on the defects and not to the penetration of new vortices.Comment: 14 pgs. RevTex, typos and figures corrected. Submitted to Phys. Rev.
Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography
In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi
The Close AGN Reference Survey (CARS): Tracing the circumnuclear star formation in the super-Eddington NLS1 Mrk 1044
The host galaxy conditions for rapid supermassive black hole growth are
poorly understood. Narrow-line Seyfert 1 (NLS1) galaxies often exhibit high
accretion rates and are hypothesized to be prototypes of active galactic nuclei
(AGN) at an early stage of their evolution. We present VLT MUSE NFM-AO
observations of Mrk 1044, the nearest super-Eddington accreting NLS1. Together
with archival MUSE WFM data we aim to understand the host galaxy processes that
drive Mrk 1044's black hole accretion. We extract the faint stellar continuum
emission from the AGN-deblended host and perform spatially resolved emission
line diagnostics with an unprecedented resolution. Combining both MUSE WFM and
NFM-AO observations, we use a kinematic model of a thin rotating disk to trace
the stellar and ionized gas motion from 10kpc down to 30pc around the
nucleus. Mrk 1044's stellar kinematics follow circular rotation, whereas the
ionized gas shows tenuous spiral features in the center. We resolve a compact
star forming circumnuclear ellipse (CNE) that has a semi-minor axis of
306pc. Within this CNE, the gas is metal rich and its line ratios are
entirely consistent with excitation by star formation. With an integrated SFR
of the CNE contributes 27% of
the galaxy-wide star formation. We conclude that Mrk 1044's nuclear activity
has not yet affected the circumnuclear star formation. Thus, Mrk 1044 is
consistent with the idea that NLS1s are young AGN. A simple mass budget
consideration suggests that the circumnuclear star formation and AGN phase are
connected and the patterns in the ionized gas velocity field are a signature of
the ongoing AGN feeding.Comment: accepted for publication in A&A, 17 pages, 14 figures, 1 table, for
Fig. 5 associated animation see https://youtube.com/watch?v=H_WSgWJSCf
Current-spin-density functional study of persistent currents in quantum rings
We present a numerical study of persistent currents in quantum rings using
current spin density functional theory (CSDFT). This formalism allows for a
systematic study of the joint effects of both spin, interactions and impurities
for realistic systems. It is illustrated that CSDFT is suitable for describing
the physical effects related to Aharonov-Bohm phases by comparing energy
spectra of impurity-free rings to existing exact diagonalization and
experimental results. Further, we examine the effects of a symmetry-breaking
impurity potential on the density and current characteristics of the system and
propose that narrowing the confining potential at fixed impurity potential will
suppress the persistent current in a characteristic way.Comment: 7 pages REVTeX, including 8 postscript figure
The ac magnetic response of mesoscopic type II superconductors
The response of mesoscopic superconductors to an ac magnetic field is
numerically investigated on the basis of the time-dependent Ginzburg-Landau
equations (TDGL). We study the dependence with frequency and dc
magnetic field of the linear ac susceptibility
in square samples with dimensions of the order of the London penetration depth.
At the behavior of as a function of agrees very well
with the two fluid model, and the imaginary part of the ac susceptibility,
, shows a dissipative a maximum at the frequency
. In the presence of a magnetic field a
second dissipation maximum appears at a frequency . The most
interesting behavior of mesoscopic superconductors can be observed in the
curves obtained at a fixed frequency. At a fixed number of
vortices, continuously increases with increasing . We
observe that the dissipation reaches a maximum for magnetic fields right below
the vortex penetration fields. Then, after each vortex penetration event, there
is a sudden suppression of the ac losses, showing discontinuities in
at several values of . We show that these
discontinuities are typical of the mesoscopic scale and disappear in
macroscopic samples, which have a continuos behavior of . We
argue that these discontinuities in are due to the effect of
{\it nascent vortices} which cause a large variation of the amplitude of the
order parameter near the surface before the entrance of vortices.Comment: 12 pages, 9 figures, RevTex
- …