Strong Correlation to Weak Correlation Phase Transition in Bilayer Quantum Hall Systems

At small layer separations, the ground state of a nu=1 bilayer quantum Hall system exhibits spontaneous interlayer phase coherence and has a charged-excitation gap E_g. The evolution of this state with increasing layer separation d has been a matter of controversy. In this letter we report on small system exact diagonalization calculations which suggest that a single phase transition, likely of first order, separates coherent incompressible (E_g >0) states with strong interlayer correlations from incoherent compressible states with weak interlayer correlations. We find a dependence of the phase boundary on d and interlayer tunneling amplitude that is in very good agreement with recent experiments.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. Let

A comparative study of depression between Korean and Scottish mothers at their two important life-stages

This is a comparative study of the depression experienced by Korean and Scottish mothers at two life stages: the postnatal stage; and the stage where the child is ready to leave secondary school education. The study investigates: (1) differences in depression scores between the two life stages as well as between the two cultures; (2) the relationship between depression and (a) the attributional style of mothers in respect of matters concerning their child, (b) social support system, (c) recent life events; (3) how these relationships vary with the life stage of the mother and cultural influences, and (4) what is the most important related factor of depression for these mothers. The study is based on a sample of 361 middle class mothers (216 Korean and 145 Scottish mothers). Depression was assessed by using the Beck Depression Inventory (1978), while attributional style was measured by using the Mother's Role Questionnaire which was specially designed for this project. The social support system was measured by the Social Support Inventory which was also designed specifically for this project. Life events were assessed by using the relevant part of the Miller's Coping Schedule (1987), which was also revised for the purpose of this research. Main results A. Depression: (1) Within each culture there were no significant differences in the levels of depression experienced by the mothers at the two life stages sampled. (2) Cultural differences in depression were found: (a) Korean mothers, at both life stages, showed significantly higher total depression scores than did their Scottish counterparts. (b) Korean mothers showed significantly higher scores overall items in the Beck Depression Inventory not only somatic scales but also cognitive-affective ones. B. Relationships between depression and independent variables: (1) a) A significant relationship between the social support system and depression scores of mothers was found. This was particularly notable in the case of the support received from other people. b) Cross-cultural sub-groups showed significantly different support systems. i) Support systems were more highly related with the depression scores of the Scottish than the Korean mothers. ii) Overall areas of the support systems related better with depression scores of the Scottish mothers, whereas practical help did for the Korean mothers, especially for the old Korean group. iii) The spouse was identified as the most important and effective supporter for both the Scottish groups of mothers and the young Korean mothers. (2) Although Korean mothers attributed internally and Scottish mothers attributed externally, the relationship of depression with attributional style was not significant. (3) The number of recent life events showed significant, yet low correlations with depression scores. However, no specific type of event showed a significant relationship to depression. (4) For the Korean mothers, the social support system was the only factor which was significant to the depression. With the Scottish mothers (especially the old group) the attributional style and number of recent life events were important as the social support system. These results were discussed and the theoretical implications were considered

Gallium desorption kinetics on (0001) GaN surface during the growth of GaN by molecular-beam epitaxy

Gallium (Ga) surfacedesorption behavior was investigated using reflection high-energy electron diffraction during the GaNgrowth. It was found that the desorption of Ga atoms from the (0001) GaNsurfaces under different III-V ratio dependents on the coverage of adsorbed atoms. Doing so led to desorption energies of 2.76 eV for Ga droplets, 1.24–1.89 eV for Ga under Ga-rich growth conditions, and 0.82 eV – 0.94 eV for Ga under stoichiometric growth conditions. Moreover, the variation of the GaNsurface morphology under different III-V ratios on porous templates supports the conclusion that Ga desorption energy depends on the coverage, and the III/V ratio dominates the growth mode

Experimental investigation of ventilation efficiency in a dentistry surgical room

As a response to the need to provide an acceptable thermal comfort and air quality in indoor environments, various ventilation performance indicators were developed over the years. These metrics are mainly geared towards air distribution, heat and pollutant removals. Evidence exists of influencing factors on these indicators as centered on ventilation design and operations. Unlike other indoor environments, health care environment requires better performance of ventilation system to prevent an incidence of nosocomial and other hospital acquired illnesses. This study investigates, using in-situ experiments, the ventilation efficiency in a dentistry surgical room. Thermal and hygric parameters were monitored on the air terminal devices and occupied zone over a period of one week covering both occupied and unoccupied hours. The resulting time-series parameters were used to evaluate the room's ventilation effectiveness. Also, the obtained parameters were benchmarked against ASHRAE 170 (2013) and MS1525 (2014) requirements for ventilation in health care environment and building energy efficiency respectively. The results show that the mean daily operative conditions failed to satisfy the provisions of both standards. Regarding effectiveness, the findings reveal that the surgical room ventilation is ineffective with ventilation efficiency values ranging between 0 and 0.5 indicating air distribution short-circuiting. These results suggest further investigations, through numerical simulation, on the effect of this short-circuiting on thermal comfort, infection risk assessments and possible design improvements, an endeavour that forms our next line of research inquiries

Effects of charge doping and constrained magnetization on the electronic structure of an FeSe monolayer

The electronic structural properties in the presence of constrained magnetization and a charged background are studied for a monolayer of FeSe in non-magnetic, checkerboard-, and striped-antiferromagnetic (AFM) spin configurations. First principles techniques based on the pseudopotential density functional approach and the local spin density approximation are utilized. Our findings show that the experimentally observed shape of the Fermi surface is best described by the checkerboard AFM spin pattern. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization. We estimate the strength of electronic coupling to magnetic excitations involving an increase in local moment and, separately, a partial moment transfer from one Fe atom to another. We also show that the charge doping in the FeSe can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures

Anomalous Stability of nu=1 Bilayer Quantum Hall State

We have studied the fractional and integer quantum Hall (QH) effects in a high-mobility double-layer two-dimensional electron system. We have compared the "stability" of the QH state in balanced and unbalanced double quantum wells. The behavior of the n=1 QH state is found to be strikingly different from all others. It is anomalously stable, though all other states decay, as the electron density is made unbalanced between the two quantum wells. We interpret the peculiar features of the nu=1 state as the consequences of the interlayer quantum coherence developed spontaneously on the basis of the composite-boson picture.Comment: 5 pages, 6 figure

Skyrmion Excitations in Quantum Hall Systems

Using finite size calculations on the surface of a sphere we study the topological (skyrmion) excitation in quantum Hall system with spin degree of freedom at filling factors around $\nu=1$. In the absence of Zeeman energy, we find, in systems with one quasi-particle or one quasi-hole, the lowest energy band consists of states with $L=S$, where $L$ and $S$ are the total orbital and spin angular momentum. These different spin states are almost degenerate in the thermodynamic limit and their symmetry-breaking ground state is the state with one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman energy and electron-electron interaction and the skyrmion shrinks to a spin texture of finite size. We have calculated the energy gap of the system at infinite wave vector limit as a function of the Zeeman energy and find there are kinks in the energy gap associated with the shrinking of the size of the skyrmion. breaking ground state is the state with one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman energy and electron-electronComment: 4 pages, 5 postscript figures available upon reques

Skyrmions in the Fractional Quantum Hall Effect

It is verified that, at small Zeeman energies, the charged excitations in the vicinity of 1/3 filled Landau level are skyrmions of composite fermions, analogous to the skyrmions of electrons near filling factor unity. These are found to be relevant, however, only at very low magnetic fields.Comment: 13 pages including 2 postscript figures; accepted for publication in Solid State Communications (1996

Structural “δ doping” to control local magnetization in isovalent oxide heterostructures

Modulation and δ -doping strategies, in which atomically thin layers of charged dopants are precisely deposited within a heterostructure, have played enabling roles in the discovery of new physical behavior in electronic materials. Here, we demonstrate a purely structural “ δ -doping” strategy in complex oxide heterostructures, in which atomically thin manganite layers are inserted into an isovalent manganite host, thereby modifying the local rotations of corner-connected MnO 6 octahedra. Combining scanning transmission electron microscopy, polarized neutron reflectometry, and density functional theory, we reveal how local magnetic exchange interactions are enhanced within the spatially confined regions of suppressed octahedral rotations. The combined experimental and theoretical results illustrate the potential to utilize noncharge-based approaches to “doping” in order to enhance or suppress functional properties within spatially confined regions of oxide heterostructures