Electron-phonon coupling and spin-charge separation in one-dimensional Mott insulators

We examine the single-particle excitation spectrum in the one-dimensional Hubbard-Holstein model at half-filling by performing the dynamical density matrix renormalization group (DDMRG) calculation. The DDMRG results are interpreted as superposition of spectra for a spinless carrier dressed with phonons. The superposition is a consequence of robustness of the spin-charge separation against electron-phonon coupling. The separation is in contrast to the coupling between phonon and spin degrees of freedom in two-dimensional systems. We discuss implication of the results of the recent angle-resolved photoemission spectroscopy measurements on SrCuO${}_{2}$.Comment: 5 pages, 4 figures. submitted to the Physical Review Letter

Critical behavior of the S=3/2 antiferromagnetic Heisenberg chain

Using the density-matrix renormalization-group technique we study the long-wavelength properties of the spin S=3/2 nearest-neighbor Heisenberg chain. We obtain an accurate value for the spin velocity v=3.8+- 0.02, in agreement with experiment. Our results show conclusively that the model belongs to the same universality class as the S=1/2 Heisenberg chain, with a conformal central charge c=1 and critical exponent eta=1Comment: RevTeX (version 3.0), 4 twocolumn pages with 4 embedded figure

Brief report: Maternal posttraumatic stress symptoms are related to adherence to their child's diabetes treatment regimen.

Although research suggests that posttraumatic stress disorder symptoms in relation to physical health diagnoses may be related to poor adherence to treatment regimens, so far, whether parental posttraumatic stress disorder symptoms have an impact on their child's adherence to insulin-dependent diabetes mellitus treatment has not been investigated. Using self-report questionnaires, the present study found that children of mothers who have posttraumatic stress disorder symptoms in relation to their child's diagnosis of type I diabetes showed poorer adherence to treatment than the children of mothers without posttraumatic stress disorder. However, this was only the case for younger children (aged 0-8 years) where mothers played a more active role in their child's treatment

The psychological impact of stillbirth on women: a systematic review.

This systematic review explored the psychological impact of stillbirth (from 20 weeks gestation) on mothers. A search was conducted in the National Library for Health and Web of Science, Cochrane Review, and Google Scholar. A secondary search based on results from the preliminary search was undertaken. A systematic search identified 26 articles (8 qualitative, 18 quantitative studies), which met criteria and were reviewed according to guidelines. The findings revealed that stillbirth is a distressing experience that can result in high levels of psychological symptoms including anxiety, depression, distress, and negative well-being. Symptoms appear to be highest in the first few months post loss although there is evidence to suggest that for some, symptoms may persist up to 3 years. The long-lasting impact of stillbirth on women was echoed in the qualitative research. Risk factors for higher levels of anxious and depressive symptoms included higher parity at the time of loss and not being married. Social support in particular was identified to be beneficial for women post loss. Longitudinal studies utilizing designs which permit causality to be determined are required to explore the specific experience of stillbirth. Further exploration of risk and protective factors, cultural beliefs, and the impact on partner relationships is needed. Clinical implications of the findings are discussed in light of current guidance

Polaron in t-J model

We present numeric results for ground state and angle resolved photoemission spectra (ARPES) for single hole in t-J model coupled to optical phonons. The systematic-error free diagrammatic Monte Carlo is employed where the Feynman graphs for the Matsubara Green function in imaginary time are summed up completely with respect to phonons variables, while magnetic variables are subjected to non-crossing approximation. We obtain that at electron-phonon coupling constants relevant for high Tc cuprates the polaron undergoes self-trapping crossover to strong coupling limit and theoretical ARPES demonstrate features observed in experiment: a broad peak in the bottom of the spectra has momentum dependence which coincides with that of hole in pure t-J model.Comment: 4 pages, 4 figure

Anisotropic optical response of the mixed-valent Mott-Hubbard insulator NaCu2O2

We report the results of a comprehensive spectroscopic ellipsometry study of NaCu2O2, a compound composed of chains of edge-sharing Cu2+O4 plaquettes and planes of Cu1+ ions in a O-Cu1+-O dumbbell configuration, in the spectral range 0.75-6.5 eV at temperatures 7 -300 K. The spectra of the dielectric function for light polarized parallel to the Cu1+ planes reveal a strong in-plane anisotropy of the interband excitations. Strong and sharp absorption bands peaked at 3.45 eV (3.7 eV) dominate the spectra for polarization along (perpendicular) to the Cu2+O2 chains. They are superimposed on flat and featureless plateaux above the absorption edges at 2.25 eV (2.5 eV). Based on density-functional calculations, the anomalous absorption peaks can be assigned to transitions between bands formed by Cu1+ 3dxz(dyz) and Cu2+ 3dxy orbitals, strongly hybridized with O pstates. The major contribution to the background response comes from transitions between Cu1+ 3dz2 and 4px(py) bands. This assignment accounts for the measured in-plane anisotropy. The dielectric response along the Cu2+O2 chains develops a weak two-peak structure centered at 2.1 and 2.65 eV upon cooling below 100 K, along with the appearance of spin correlations along the Cu2+O2 chains. These features bear a striking resemblance to those observed in the single-valent Cu2+O2 chain compound LiCuVO4, which were identified as an exciton doublet associated with transitions to the upper Hubbard band that emerges as a consequence of the long-range Coulomb interaction between electrons on neighboring Cu2+ sites along the chains. An analysis of the spectral weights of these features yields the parameters characterizing the on-site and long-range Coulomb interactions.Comment: 12 pages, 12 figure

Exciton doublet in the Mott-Hubbard LiCuVO4_4 insulator identified by spectral ellipsometry

Spectroscopic ellipsometry was used to study the dielectric function of LiCuVO$_{4}$, a compound comprised of chains of edge-sharing CuO$_4$ plaquettes, in the spectral range (0.75 - 6.5) eV at temperatures (7-300) K. For photon polarization along the chains, the data reveal a weak but well-resolved two-peak structure centered at 2.15 and 2.95 eV whose spectral weight is strongly enhanced upon cooling near the magnetic ordering temperature. We identify these features as an exciton doublet in the Mott-Hubbard gap that emerges as a consequence of the Coulomb interaction between electrons on nearest and next-nearest neighbor sites along the chains. Our results and methodology can be used to address the role of the long-range Coulomb repulsion for compounds with doped copper-oxide chains and planes.Comment: 4 pages with 4 figures and EPAPS supplementary online material (3 pages with 4 figures), accepted in Phys. Rev. Let

Posttraumatic stress disorder in mothers of individuals with Anorexia Nervosa.

This pilot study aimed to investigate the prevalence of maternal posttraumatic stress (PTSD), anxiety and depressive symptoms and what aspects of having a child with anorexia nervosa (AN) are perceived as traumatic by the mothers. Thirty-one mothers of daughters with AN completed a range of self-report questionnaires and a structured clinical interview. Higher rates of anxiety, depression and PTSD symptoms were found in mothers than in the general UK population. Mothers reported acute traumatic stressors during the course of AN, such as 'thinking their daughter was about to die or dead', 'seeing or consenting to their daughter being tube-fed'. We also found that mothers rated chronic aspects of their daughter's AN as very severely distressing, such as 'worrying about permanent damage to daughter's health'. Results suggest that maternal mental health should be kept in mind during assessments of individuals with eating disorders and referral for a service in their own right might be indicated

Credit Information Sharing and Its Link to Financial Inclusion and Financial Intermediation

In this article, several regression analyses are conducted to analyse the relationship of credit information sharing (by both private credit bureaus and public credit registries) with financial inclusion and financial intermediation. We find that there is a positive relationship between information sharing mechanisms and financial inclusion (measured by account (at a financial institution), borrowed from a financial institution, and domestic credit). We do not find significant results for bank performance parameters. Whereas this is the case with bank non-performing loans, the data do not allow (due to low R2) drawing conclusions on other parameters such as lending minus inflation rate or bank concentration