658 research outputs found

    Energy, interaction, and photoluminescence of spin-reversed quasielectrons in fractional quantum Hall systems

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    The energy and photoluminescence spectra of a two-dimensional electron gas in the fractional quantum Hall regime are studied. The single-particle properties of reversed-spin quasielectrons (QER_{\rm R}'s) as well as the pseudopotentials of their interaction with one another and with Laughlin quasielectrons (QE's) and quasiholes (QH's) are calculated. Based on the short-range character of the QER_{\rm R}--QER_{\rm R} and QER_{\rm R}--QE repulsion, the partially unpolarized incompressible states at the filling factors ν=411\nu={4\over11} and 513{5\over13} are postulated within Haldane's hierarchy scheme. To describe photoluminescence, the family of bound h(h(QER)n_{\rm R})_n states of a valence hole hh and nn QER_{\rm R}'s are predicted in analogy to the found earlier fractionally charged excitons hhQEn_n. The binding energy and optical selection rules for both families are compared. The hhQER_{\rm R} is found radiative in contrast to the dark hhQE, and the h(h(QER)2_{\rm R})_2 is found non-radiative in contrast to the bright hhQE2_2.Comment: 9 pages, 6 figure

    Negatively Charged Excitons and Photoluminescence in Asymmetric Quantum Well

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    We study photoluminescence (PL) of charged excitons (XX^-) in narrow asymmetric quantum wells in high magnetic fields B. The binding of all XX^- states strongly depends on the separation δ\delta of electron and hole layers. The most sensitive is the ``bright'' singlet, whose binding energy decreases quickly with increasing δ\delta even at relatively small B. As a result, the value of B at which the singlet--triplet crossing occurs in the XX^- spectrum also depends on δ\delta and decreases from 35 T in a symmetric 10 nm GaAs well to 16 T for δ=0.5\delta=0.5 nm. Since the critical values of δ\delta at which different XX^- states unbind are surprisingly small compared to the well width, the observation of strongly bound XX^- states in an experimental PL spectrum implies virtually no layer displacement in the sample. This casts doubt on the interpretation of PL spectra of heterojunctions in terms of XX^- recombination

    Exclusion Statistics of Quasiparticles in Condensed States of Composite Fermion Excitations

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    The exclusion statistics of quasiparticles is found at any level of the hierarchy of condensed states of composite fermion excitations (for which experimental indications have recently been found). The hierarchy of condensed states of excitations in boson Jain states is introduced and the statistics of quasiparticles is found. The quantum Hall states of charged α\alpha-anyons (α\alpha -- the exclusion statistics parameter) can be described as incompressible states of (α+2p)(\alpha+2p)-anyons (2p2p -- an even number).Comment: 4 page

    Effect of B-site Dopants on Magnetic and Transport Properties of LaSrCoRuO6_6

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    Effect of Co, Ru and Cu substitution at B and B' sites on the magnetic and transport properties of LaSrCoRuO6_6 have been investigated. All the doped compositions crystallize in the monoclinic structure in the space group P21/nP2_1/n indicating a double perovskite structure. While the magnetization and conductivity increase in Co and Ru doped compounds, antiferromagnetism is seen to strengthen in the Cu doped samples. These results are explained on the basis of a competition between linear Co-O-Ru-O-Co and perpendicular Co-O-O-Co antiferromagnetic interactions and due to formation of Ru-O-Ru ferromagnetic networks

    Association between first caesarean delivery and adverse outcomes in subsequent pregnancy: a retrospective cohort study

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    BACKGROUND:Few studies have explored the association between a previous caesarean section (CS) and adverse perinatal outcomes in a subsequent pregnancy, especially in women who underwent a non-indicated CS in their first delivery. We designed this study to compare the perinatal outcomes of a subsequent pregnancy in women who underwent spontaneous vaginal delivery (SVD) or CS in their first delivery. METHODS:This retrospective cohort study included women who underwent singleton deliveries at the International Peace Maternity and Child Health Hospital from January 2013 to December 2016. Data on the perinatal outcomes of all the women were extracted from the medical records. Multivariate logistic regression was conducted to assessed the association between CS in the first delivery and adverse perinatal outcomes in the subsequent pregnancy. RESULTS:CS delivery in the subsequent pregnancy was more likely for women who underwent CS in their first birth than for women with previous SVD (97.3% versus 13.2%). CS in the first birth was also associated with a significantly increased risk of adverse outcomes in the subsequent pregnancy, especially in women who underwent a non-indicated CS. Adverse perinatal outcomes included pregnancy-induced hypertension [adjusted odds ratio (OR), 95% confidence interval (CI): 2.20, 1.59-3.05], gestational diabetes mellitus (1.82, 1.57-2.11), gestational anaemia (1.27, 1.05-1.55), placenta previa (3.18, 2.15-4.71), placenta accreta (2.75, 1.75-4.31), and polyhydramnios (2.60, 1.57-4.31) in the mother and preterm delivery (1.37, 1.06-1.78), low birth weight (3.78, 2.07-6.90), macrosomia (5.04, 3.95-6.44), and neonatal jaundice (1.72, 1.39-2.14) in the baby. CONCLUSIONS:CS in the first delivery markedly increases the risk of repeated CS and maternal-fetal complications in the subsequent pregnancy, especially in women with a non-indicated CS.Hong-Tao Hu, Jing-Jing Xu, Jing Lin, Cheng Li, Yan-Ting Wu, Jian-Zhong Sheng, Xin-Mei Liu and He-Feng Huan

    A Topological Study of Chaotic Iterations. Application to Hash Functions

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    International audienceChaotic iterations, a tool formerly used in distributed computing, has recently revealed various interesting properties of disorder leading to its use in the computer science security field. In this paper, a comprehensive study of its topological behavior is proposed. It is stated that, in addition to being chaotic as defined in the Devaney's formulation, this tool possesses the property of topological mixing. Additionally, its level of sensibility, expansivity, and topological entropy are evaluated. All of these properties lead to a complete unpredictable behavior for the chaotic iterations. As it only manipulates binary digits or integers, we show that it is possible to use it to produce truly chaotic computer programs. As an application example, a truly chaotic hash function is proposed in two versions. In the second version, an artificial neural network is used, which can be stated as chaotic according to Devaney

    Non-Markovian dynamics for an open two-level system without rotating wave approximation: Indivisibility versus backflow of information

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    By use of the two measures presented recently, the indivisibility and the backflow of information, we study the non-Markovianity of the dynamics for a two-level system interacting with a zero-temperature structured environment without using rotating wave approximation (RWA). In the limit of weak coupling between the system and the reservoir, and by expanding the time-convolutionless (TCL) generator to the forth order with respect to the coupling strength, the time-local non-Markovian master equation for the reduced state of the system is derived. Under the secular approximation, the exact analytic solution is obtained and the sufficient and necessary conditions for the indivisibility and the backflow of information for the system dynamics are presented. In the more general case, we investigate numerically the properties of the two measures for the case of Lorentzian reservoir. Our results show the importance of the counter-rotating terms to the short-time-scale non-Markovian behavior of the system dynamics, further expose the relations between the two measures and their rationality as non-Markovian measures. Finally, the complete positivity of the dynamics of the considered system is discussed
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