48,811 research outputs found
Single exciton spectroscopy of single-Mn doped InAs quantum dots
The optical spectroscopy of a single InAs quantum dot doped with a single Mn
atom is studied using a model Hamiltonian that includes the exchange
interactions between the spins of the quantum dot electron-hole pair, the Mn
atom and the acceptor hole. Our model permits to link the photoluminescence
spectra to the Mn spin states after photon emission. We focus on the relation
between the charge state of the Mn, or , and the different spectra
which result through either band-to-band or band-to-acceptor transitions. We
consider both neutral and negatively charged dots. Our model is able to account
for recent experimental results on single Mn doped InAs PL spectra and can be
used to account for future experiments in GaAs quantum dots. Similarities and
differences with the case of single Mn doped CdTe quantum dots are discussed.Comment: 15 pages, 9 figure
: Confronting theory and lattice simulations
We consider a recent -matrix analysis by Albaladejo {\it et al.}, [Phys.\
Lett.\ B {\bf 755}, 337 (2016)] which accounts for the and
coupled--channels dynamics, and that successfully describes the
experimental information concerning the recently discovered .
Within such scheme, the data can be similarly well described in two different
scenarios, where the is either a resonance or a virtual state. To
shed light into the nature of this state, we apply this formalism in a finite
box with the aim of comparing with recent Lattice QCD (LQCD) simulations. We
see that the energy levels obtained for both scenarios agree well with those
obtained in the single-volume LQCD simulation reported in Prelovsek {\it et
al.} [Phys.\ Rev.\ D {\bf 91}, 014504 (2015)], making thus difficult to
disentangle between both possibilities. We also study the volume dependence of
the energy levels obtained with our formalism, and suggest that LQCD
simulations performed at several volumes could help in discerning the actual
nature of the intriguing state
Dual regimes of ion migration in high repetition rate femtosecond laser inscribed waveguides
Ion migration in high repetition rate femtosecond laser inscribed waveguides
is currently being reported in different optical glasses. For the first time we
discuss and experimentally demonstrate the presence of two regimes of ion
migration found in laser written waveguides. Regime-I, corresponds to the
initial waveguide formation mainly via light element migration (in our case
atomic weight < 31u), whereas regime-II majorly corresponds to the movement of
heavy elements. This behavior brings attention to a problem which has never
been analyzed before and that affects laser written active waveguides in which
active ions migrate changing their local spectroscopic properties. The
migration of active ions may in fact detune the pre-designed optimal values of
active photonic devices. This paper experimentally evidences this problem and
provides solutions to avert it.Comment: 4 pages, 5 figure
Excited-state quantum phase transitions in a two-fluid Lipkin model
Background: Composed systems have became of great interest in the framework
of the ground state quantum phase transitions (QPTs) and many of their
properties have been studied in detail. However, in these systems the study of
the so called excited-state quantum phase transitions (ESQPTs) have not
received so much attention.
Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is
presented in this work. The study is performed through the Hamiltonian
diagonalization for selected values of the control parameters in order to cover
the most interesting regions of the system phase diagram. [Method:] A
Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting
boson model (IBM) is diagonalized for selected values of the parameters and
properties such as the density of states, the Peres lattices, the
nearest-neighbor spacing distribution, and the participation ratio are
analyzed.
Results: An overview of the spectrum of the two-fluid Lipkin model for
selected positions in the phase diagram has been obtained. The location of the
excited-state quantum phase transition can be easily singled out with the Peres
lattice, with the nearest-neighbor spacing distribution, with Poincar\'e
sections or with the participation ratio.
Conclusions: This study completes the analysis of QPTs for the two-fluid
Lipkin model, extending the previous study to excited states. The ESQPT
signatures in composed systems behave in the same way as in single ones,
although the evidences of their presence can be sometimes blurred. The Peres
lattice turns out to be a convenient tool to look into the position of the
ESQPT and to define the concept of phase in the excited states realm
Synthesis of Y1BaCu3O(x) superconducting powders by intermediate phase reactions
A procedure for synthesizing Y1Ba2Cu3O(x) by solid state reactions was developed. The method is based on the use of barium compounds, previously synthesized, as intermediate phases for the process. The reaction kinetics of this procedure were established between 860 C and 920 C. The crystal structure and the presence of second phases were studied by means of XRD. The sintering behavior and ceramic parameters were also determined. The orthorhombic type-I structure was obtained on the synthesized bodies after a cooling cycle in an air atmosphere. Superconducting transition took place at 91 K. Sintering densities higher than 95 percent D sub th were attained at temperatures below 940 C
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