Hole dynamics in a quantum antiferromagnet beyond the retraceable path approximation

The one-hole spectral weight for two chains and two dimensional lattices is studied numerically using a new method of analysis of the spectral function within the Lanczos iteration scheme: the Lanczos spectra decoding method. This technique is applied to the $t-J_z$ model for $J_z \to 0$, directly in the infinite size lattice. By a careful investigation of the first 13 Lanczos steps and the first 26 ones for the two dimensional and the two chain cases respectively, we get several new features of the one-hole spectral weight. A sharp incoherent peak with a clear momentum dispersion is identified, together with a second broad peak at higher energy. The spectral weight is finite up to the Nagaoka energy where it vanishes in a non-analytic way. Thus the lowest energy of one hole in a quantum antiferromagnet is degenerate with the Nagaoka energy in the thermodynamic limit.Comment: RevTeX 3.0, SISSA preprint 156/93/CM/MB, 10 pages + postscript file appended, contains more accurate calculations in Fig.

Even and odd-frequency pairing correlations in 1-D t-J-h model: a comparative study

An equal time version of odd-frequency pairing for a generalized $t-J$ model is introduced. It is shown that the composite operators describing binding of Cooper pairs with magnetization fluctuations naturally appear in this approach. The pairing correlations in both BCS and odd-frequency channels are investigated exactly in 1D systems with up to 16 sites. Our results indicate that at some range of parameters odd-frequency correlations become comparable, however smaller than BCS pairing correlations. It is speculated that the spin and density fluctuations in the frustrated model lead to the enhancement of the odd gap susceptibilities. 4 postscript figure files are attached at the bottom of the tex file.Comment: 6 pages + 4 figure

Inequalities in child development at school entry: a repeated cross-sectional analysis of the Australian Early Development Census 2009–2018

Background: Australia is the only developed country to consistently undertake a developmental census of its children nationwide. The repeated collection of the Australian Early Development Census (AEDC) has provided an unprecedented opportunity to examine the prevalence of developmental vulnerability across Australia's states and territories, the socio-economic distribution of developmental vulnerability across jurisdictions, and how these distributions might have changed over time. Methods: This study employed multivariable logistic regressions to estimate the probability of developmental vulnerability within each jurisdiction and AEDC collection year (2009 to 2018), adjusting for jurisdictional differences in socio-demographic characteristics. To explore socio-economic inequalities in child development, adjusted slope index of inequality (SII) models were utilised. Findings: The results of this study found reductions in the adjusted prevalence of developmental vulnerability over time in Western Australia (26% to 20%) and Queensland (30% to 25%), with an increase observed in the Australian Capital Territory (27% to 30%). Analysis also indicated an increase in socio-economic inequalities over time in the Northern Territory (+12%), the Australian Capital Territory (+6%) and Tasmania (+4%). Sensitivity analysis found these effects to be robust with an alternative measure of socio-economic position. Interpretation: There is considerable variation in the prevalence and socio-economic inequalities in developmental vulnerability across Australia's jurisdictions. Future research should explore the policy drivers in early childhood education and health contributing to the findings of this study, with a particular focus on jurisdictions where there have been notable changes in developmental vulnerability and socio-economic inequality over time. Funding: Analyses were funded under research contract by the Department of Education, Skills and Employment. Prof Brinkman is supported by a National Health and Medical Research Council fellowship, APP1160185.Luke R. Collier, Tess Gregory, Yasmin Harman-Smith, Angela Gialamas, Sally A. Brinkma

Hole dynamics and photoemission in a t-J model for SrCu_2(BO_3)_2

The motion of a single hole in a t-J model for the two-dimensional spin-gap compound SrCu_2(BO_3)_2 is investigated. The undoped Heisenberg model for this system has an exact dimer eigenstate and shows a phase transition between a dimerized and a Neel phase at a certain ratio of the magnetic couplings. We calculate the photoemission spectrum in the disordered phase using a generalized spin-polaron picture. By varying the inter-dimer hopping parameters we find a cross-over between a narrow quasiparticle band regime known from other strongly correlated systems and free-fermion behavior. The hole motion in the Neel-ordered phase is also briefly considered.Comment: 4 pages, 3 fig

Spin polarons in triangular antiferromagnets

The motion of a single hole in a 2D triangular antiferromagnet is investigated using the t-J model. The one-hole states are described by strings of spin deviations around the hole. Using projection technique the one-hole spectral function is calculated. For large J/t we find low-lying quasiparticle-like bands which are well separated from an incoherent background by a gap of order J. However, for small J/t this gap vanishes and the spectrum becomes broad over an energy range of several t. The results are compared with SCBA calculations and numerical data.Comment: 4 pages, 6 figs, to be publish in PR

Basic epidemiology of wellbeing among children and adolescents: a cross-sectional population level study

Wellbeing and mental health are fundamental rights of children and adolescents essential for sustainable development. Understanding the epidemiology of child and adolescent wellbeing is essential to informing population health approaches to improving wellbeing and preventing mental illness. The present study estimated the prevalence of wellbeing and how wellbeing indicators were distributed across social and economic groups. This study used data from the 2019 Wellbeing and Engagement Collection; an annual census conducted in South Australian schools that measures self-reported wellbeing in students aged 8-18 years (n = 75,966). We estimated the prevalence (n, %) of low, medium and high wellbeing across five outcomes: life satisfaction, optimism, sadness, worries and happiness, overall and stratified by gender, age, language background, socio-economic position and geographical remoteness. The prevalence of low wellbeing on each indicator was: happiness 13%, optimism 16%, life satisfaction 22%, sadness 16% and worries 25%. The prevalence of low wellbeing increased with age, particularly for females. For example, 22.5% of females aged 8-10 years had high levels of worries compared to 43.6% of 15 to 18-year old females. Socioeconomic inequality in wellbeing was evident on all indicators, with 19.5% of children in the most disadvantaged communities having high levels of sadness compared to 12.5% of children in the most advantaged communities. Many children and adolescents experience low wellbeing on one or more indicators (40.7%). The scale of this problem warrants a population-level preventative health response, in addition to a clinical, individual-level responses to acute mental health needs. Universal school-based programs that support social and emotional wellbeing have a role to play in this response but need to be supported by universal and targeted responses from outside of the education system.Tess Gregory, Alanna Sincovich, Mary Brushe, Amy Finlay-Jones, Luke R.Collier, Blair Grace ... et al

Low energy and dynamical properties of a single hole in the t-Jz model

We review in details a recently proposed technique to extract information about dynamical correlation functions of many-body hamiltonians with a few Lanczos iterations and without the limitation of finite size. We apply this technique to understand the low energy properties and the dynamical spectral weight of a simple model describing the motion of a single hole in a quantum antiferromagnet: the $t-J_z$ model in two spatial dimension and for a double chain lattice. The simplicity of the model allows us a well controlled numerical solution, especially for the two chain case. Contrary to previous approximations we have found that the single hole ground state in the infinite system is continuously connected with the Nagaoka fully polarized state for $J_z \to 0$. Analogously we have obtained an accurate determination of the dynamical spectral weight relevant for photoemission experiments. For $J_z=0$ an argument is given that the spectral weight vanishes at the Nagaoka energy faster than any power law, as supported also by a clear numerical evidence. It is also shown that spin charge decoupling is an exact property for a single hole in the Bethe lattice but does not apply to the more realistic lattices where the hole can describe closed loop paths.Comment: RevTex 3.0, 40 pages + 16 Figures in one file self-extracting, to appear in Phys. Rev

Reading and numeracy attainment of children reported to child protection services: A population record linkage study controlling for other adversities

Background: Maltreated children are at risk of poor educational outcomes, but also experience greater individual, family, and neighbourhood adversities that may obscure an understanding of relationships between child protection involvement and educational attainment. Objective: To examine associations between child protection involvement and 3rd- and 5th-grade reading and numeracy attainment, while controlling multiple other adversities. Participants and Setting Participants were 56,860 Australian children and their parents from the New South Wales Child Development Study with linked multi-agency records. Methods: Multinomial logistic regressions examined associations between level of child protection involvement (Out-Of-Home Care [OOHC] placement; substantiated Risk Of Significant Harm [ROSH]; unsubstantiated ROSH; non-ROSH; and no child protection report) and standardised tests of 3rd- and 5th-grade reading and numeracy. Fully adjusted models controlled demographic, pregnancy, birth, and parental factors, and early (kindergarten) developmental vulnerabilities on literacy and numeracy, and other developmental domains (social, emotional, physical, communication). Results: All children with child protection reports were more likely to attain below average, and less likely to attain above average, 3rd- and 5th-grade reading and numeracy, including children with reports below the ROSH threshold. Children with substantiated ROSH reports who were not removed into care demonstrated the worst educational attainment, with some evidence of protective effects for children in OOHC. Conclusions: A cross-agency response to supporting educational attainment for all children reported to child protection services is required, including targeted services for children in OOHC or with substantiated ROSH reports, and referral of vulnerable families (unsubstantiated and non-ROSH cases) to secondary service organisations (intermediate intervention).Kristin R.Laurens, Fahkrul Islam, Maina Kariuki, Felicity Harris, Marilyn Chilvers ... Sally A.Brinkman ... et al