76 research outputs found
Theory of Luminescence Spectra of High-Density Electron-Hole Systems: Crossover from Excitonic Bose-Einstein Condenstation to Electron-Hole BCS State
We present a unified theory of luminescence spectra for highly excited
semiconductors, which is applicable both to the electron-hole BCS state and to
the exciton Bose-Einstein condensate. The crossover behavior between
electron-hole BCS state and exciton Bose-Einstein condensate clearly manifests
itself in the calculated luminescence spectra. The analysis is based on the
Bethe-Salpeter equation combined with the generalized
random-phase-approximation, which enables us to consider the multiple Coulomb
scattering and the quantum fluctuation associated with the center-of-mass
motion of electron-hole pairs. In the crossover regime, the calculated spectra
are essentially different from results obtained by the BCS-like mean-field
theory and the interacting Boson model. In particular, it is found that the
broad spectrum, arising from the recombination of electron-hole BCS state,
splits into the P- and P_2-luminescence bands with decreasing the particle
density. The dependence of these bands on the carrier density is in good
agreement with experiments for highly excited semiconductors.Comment: 9 pages, 4 figures, To appear in Solid State Communication
SN 2009js at the Crossroads between Normal and Subluminous Type IIP Supernovae: Optical and Mid-infrared Evolution
We present a study of SN 2009js in NGC 918. Multi-band Kanata optical photometry covering the first ~120 days shows the source to be a Type IIP SN. Reddening is dominated by that due to our Galaxy. One-year-post-explosion photometry with the New Technology Telescope and a Subaru optical spectrum 16 days post-discovery both imply a good match with the well-studied subluminous SN 2005cs. The plateau-phase luminosity of SN 2009js and its plateau duration are more similar to the intermediate luminosity IIP SN 2008in. Thus, SN 2009js shares characteristics with both subluminous and intermediate luminosity supernovae (SNe). Its radioactive tail luminosity lies between SN 2005cs and SN 2008in, whereas its quasi-bolometric luminosity decline from peak to plateau (quantified by a newly defined parameter Δlog, which measures adiabatic cooling following shock breakout) is much smaller than both the others'. We estimate the ejected mass of 56Ni to be low (~0.007 M ☉). The SN explosion energy appears to have been small, similar to that of SN 2005cs. SN 2009js is the first subluminous SN IIP to be studied in the mid-infrared. It was serendipitously caught by Spitzer at very early times. In addition, it was detected by WISE 105 days later with a significant 4.6 μm flux excess above the photosphere. The infrared excess luminosity relative to the photosphere is clearly smaller than that of SN 2004dj, which has been extensively studied in the mid-infrared. The excess may be tentatively assigned to heated dust with mass ~3 × 10–5 M ☉, or to CO fundamental emission as a precursor to dust formation
Entanglement Transfer via XXZ Heisenberg chain with DM Interaction
The role of spin-orbit interaction, arises from the Dzyaloshinski-Moriya
anisotropic antisymmetric interaction, on the entanglement transfer via an
antiferromagnetic XXZ Heisenberg chain is investigated. From symmetrical point
of view, the XXZ Hamiltonian with Dzyaloshinski-Moriya interaction can be
replaced by a modified XXZ Hamiltonian which is defined by a new exchange
coupling constant and rotated Pauli operators. The modified coupling constant
and the angle of rotations are depend on the strength of Dzyaloshinski-Moriya
interaction. In this paper we study the dynamical behavior of the entanglement
propagation through a system which is consist of a pair of maximally entangled
spins coupled to one end of the chain. The calculations are performed for the
ground state and the thermal state of the chain, separately. In both cases the
presence of this anisotropic interaction make our channel more efficient, such
that the speed of transmission and the amount of the entanglement are improved
as this interaction is switched on. We show that for large values of the
strength of this interaction a large family of XXZ chains becomes efficient
quantum channels, for whole values of an isotropy parameter in the region .Comment: 21 pages, 9 figure
A new family of matrix product states with Dzyaloshinski-Moriya interactions
We define a new family of matrix product states which are exact ground states
of spin 1/2 Hamiltonians on one dimensional lattices. This class of
Hamiltonians contain both Heisenberg and Dzyaloshinskii-Moriya interactions but
at specified and not arbitrary couplings. We also compute in closed forms the
one and two-point functions and the explicit form of the ground state. The
degeneracy structure of the ground state is also discussed.Comment: 15 pages, 1 figur
Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction
We have studied occurrence of quantum phase transition in the one-dimensional
spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi-
partite and multi-partite entanglement point of view. Using exact numerical
solutions, we are able to study such systems up to 24 qubits. The minimum of
the entanglement ratio R \tau 2/\tau 1 < 1, as a novel estimator of
QPT, has been used to detect QPT and our calculations have shown that its
minimum took place at the critical point. We have also shown both the
global-entanglement (GE) and multipartite entanglement (ME) are maximal at the
critical point for the Ising chain with added DM interaction. Using matrix
product state approach, we have calculated the tangle and concurrence of the
model and it is able to capture and confirm our numerical experiment result.
Lack of inversion symmetry in the presence of DM interaction stimulated us to
study entanglement of three qubits in symmetric and antisymmetric way which
brings some surprising results.Comment: 18 pages, 9 figures, submitte
Statistical Theory of Spin Relaxation and Diffusion in Solids
A comprehensive theoretical description is given for the spin relaxation and
diffusion in solids. The formulation is made in a general
statistical-mechanical way. The method of the nonequilibrium statistical
operator (NSO) developed by D. N. Zubarev is employed to analyze a relaxation
dynamics of a spin subsystem. Perturbation of this subsystem in solids may
produce a nonequilibrium state which is then relaxed to an equilibrium state
due to the interaction between the particles or with a thermal bath (lattice).
The generalized kinetic equations were derived previously for a system weakly
coupled to a thermal bath to elucidate the nature of transport and relaxation
processes. In this paper, these results are used to describe the relaxation and
diffusion of nuclear spins in solids. The aim is to formulate a successive and
coherent microscopic description of the nuclear magnetic relaxation and
diffusion in solids. The nuclear spin-lattice relaxation is considered and the
Gorter relation is derived. As an example, a theory of spin diffusion of the
nuclear magnetic moment in dilute alloys (like Cu-Mn) is developed. It is shown
that due to the dipolar interaction between host nuclear spins and impurity
spins, a nonuniform distribution in the host nuclear spin system will occur and
consequently the macroscopic relaxation time will be strongly determined by the
spin diffusion. The explicit expressions for the relaxation time in certain
physically relevant cases are given.Comment: 41 pages, 119 Refs. Corrected typos, added reference
EMPRESS. IV. Extremely metal-poor galaxies including very low-mass primordial systems with M* = 10^4-10^5 M and 2%-3% (O/H): high (Fe/O) suggestive of metal enrichment by hypernovae/pair-instability supernovae
Galaxie
Ultra-luminous X-ray sources and neutron-star-black-hole mergers from very massive close binaries at low metallicity
Ultra-luminous X-ray sources and neutron-star-black-hole mergers from very massive close binaries at low metallicity
Supernova spectra below strong circumstellar interaction
We construct spectra of supernovae (SNe) interacting strongly with a circumstellar medium (CSM) by adding SN templates, a blackbody
continuum, and an emission-line spectrum. In a Monte Carlo simulation we vary a large number of parameters, such as the SN
type, brightness and phase, the strength of the CSM interaction, the extinction, and the signal to noise ratio (S/N) of the observed
spectrum. We generate more than 800 spectra, distribute them to ten different human classifiers, and study how the different simulation
parameters affect the appearance of the spectra and their classification. The SNe IIn showing some structure over the continuum were
characterized as “SNe IInS” to allow for a better quantification. We demonstrate that the flux ratio of the underlying SN to the
continuum fV is the single most important parameter determining whether a spectrum can be classified correctly. Other parameters,
such as extinction, S/N, and the width and strength of the emission lines, do not play a significant role. Thermonuclear SNe get
progressively classified as Ia-CSM, IInS, and IIn as fV decreases. The transition between Ia-CSM and IInS occurs at fV ∼ 0.2−0.3. It
is therefore possible to determine that SNe Ia-CSM are found at the (un-extincted) magnitude range −19.5 > M > −21.6, in very good
agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = −20.1. The literature sample of SNe Ia-CSM
shows an association with 91T-like SNe Ia. Our experiment does not support that this association can be attributed to a luminosity bias
(91T-like being brighter than normal events). We therefore conclude that this association has real physical origins and we propose that
91T-like explosions result from single degenerate progenitors that are responsible for the CSM. Despite the spectroscopic similarities
between SNe Ibc and SNe Ia, the number of misclassifications between these types was very small in our simulation and mostly at low
S/N. Combined with the SN luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc
constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Hα profiles vary
with fV . SNe IIn fainter than M = −17.2 are unable to mask SNe IIP brighter than M = −15. A more advanced simulation, including
radiative transfer, shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement
with real data
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