Asymptotically exact trial wave functions for yrast states of rotating Bose gases

We revisit the composite fermion (CF) construction of the lowest angular momentum yrast states of rotating Bose gases with weak short range interaction. For angular momenta at and below the single vortex, $L \leq N$, the overlaps between these trial wave functions and the corresponding exact solutions {\it increase} with increasing system size and appear to approach unity in the thermodynamic limit. In the special case $L=N$, this remarkable behaviour was previously observed numerically. Here we present methods to address this point analytically, and find strongly suggestive evidence in favour of similar behaviour for all $L \leq N$. While not constituting a fully conclusive proof of the converging overlaps, our results do demonstrate a striking similarity between the analytic structure of the exact ground state wave functions at $L \leq N$, and that of their CF counterparts. Results are given for two different projection methods commonly used in the CF approach

Disorder and interactions in quantum Hall ferromagnets near ν=1\nu=1

We report on a finite-size Hartree-Fock study of the competition between disorder and interactions in a two-dimensional electron gas near Landau level filling factor $\nu=1$. The ground state at $\nu=1$ evolves with increasing disorder from a fully spin-polarized ferromagnet with a charge gap, to a partially spin-polarized ferromagnetic Anderson insulator, to a quasi-metallic paramagnet at the critical point between $i=0$ and $i=2$ quantum Hall plateaus. Away from $\nu=1$, the ground state evolves from a ferromagnetic Skyrmion quasiparticle glass, to a conventional quasiparticle glass, and finally to a conventional Anderson insulator. We comment on signatures of these different regimes in low-temperature transport and NMR lineshape and peak position data.Comment: 10 pages, 8 figures, submitted to PR

Electronic Interface Reconstruction at Polar-Nonpolar Mott Insulator Heterojunctions

We report on a theoretical study of the electronic interface reconstruction (EIR) induced by polarity discontinuity at a heterojunction between a polar and a nonpolar Mott insulators, and of the two-dimensional strongly-correlated electron systems (2DSCESs) which accompany the reconstruction. We derive an expression for the minimum number of polar layers required to drive the EIR, and discuss key parameters of the heterojunction system which control 2DSCES properties. The role of strong correlations in enhancing confinement at the interface is emphasized.Comment: 7 pages, 6 figures, some typos correcte

Quantum Dots in Strong Magnetic Fields: Stability Criteria for the Maximum Density Droplet

In this article we discuss the ground state of a parabolically confined quantum dots in the limit of very strong magnetic fields where the electron system is completely spin-polarized and all electrons are in the lowest Landau level. Without electron-electron interactions the ground state is a single Slater determinant corresponding to a droplet centered on the minimum of the confinement potential and occupying the minimum area allowed by the Pauli exclusion principle. Electron-electron interactions favor droplets of larger area. We derive exact criteria for the stability of the maximum density droplet against edge excitations and against the introduction of holes in the interior of the droplet. The possibility of obtaining exact results in the strong magnetic field is related to important simplifications associated with broken time-reversal symmetry in a strong magnetic field.Comment: 17 pages, 5 figures (not included), RevTeX 3.0. (UCF-CM-93-002

Neonatal weight loss in breast and formula-fed infants

We have observed an increase in the number of breast fed babies presenting with dehydration and/or failure to thrive because of lactation failure and non-recognition of feeding problems. Recent reports1,2 support this experience and recommend monitoring of the weight of infants through the neonatal period. However, these reports acknowledge uncertainty as to what actually constitutes normal neonatal weight loss. Maisels and colleagues published two studies which have been quoted as giving guidance on normal loss. Both studies were designed primarily to study factors that influence breast milk jaundice. The first3 reported a mean weight loss of about 6% in 100 unselected well babies during the first 3 days. The subsequent study4 reported a mean weight loss of 6.86% in 186 infants. The timescale over which babies were weighed was not clearly indicated, although it may have only been 2-3 days. The sample was neither population based nor randomly selected, being largely preselected because of the presence of more pronounced jaundice. The distribution of data points for early neonatal weight loss are likely to be skewed, yet both studies reported the results as mean (SD). Owing to the design and method of data presentation, these studies cannot reliably inform the debate as to what constitutes the norm. Marchini and colleagues published reports also designed primarily to study other issues. One5 indicated a mean early weight loss of 5.7%. Measurements were recorded over a three day period, and no indication is given of the skewness of the data. Another study6 reported a median weight loss of about 6% recorded over a four day period. At least one baby lost > 15% of his/her birth weight during this time, but there is no clear information as to the frequency with which more extreme degrees of weight loss are observed

Edge State Tunneling in a Split Hall Bar Model

In this paper we introduce and study the correlation functions of a chiral one-dimensional electron model intended to qualitatively represent narrow Hall bars separated into left and right sections by a penetrable barrier. The model has two parameters representing respectively interactions between top and bottom edges of the Hall bar and interactions between the edges on opposite sides of the barrier. We show that the scaling dimensions of tunneling processes depend on the relative strengths of the interactions, with repulsive interactions across the Hall bar tending to make breaks in the barrier irrelevant. The model can be solved analytically and is characterized by a difference between the dynamics of even and odd Fourier components. We address its experimental relevance by comparing its predictions with those of a more geometrically realistic model that must be solved numerically.Comment: 13 pages, including 4 figures,final version as publishe

Optical spin transfer in ferromagnetic semiconductors

Circularly polarized laser pulses that excite electron-hole pairs across the band gap of (III,Mn)V ferromagnetic semiconductors can be used to manipulate and to study collective magnetization dynamics. The initial spin orientation of a photocarrier in a (III,V) semiconductors is determined by the polarization state of the laser. We show that the photocarrier spin can be irreversibly transferred to the collective magnetization, whose dynamics can consequently be flexibly controlled by suitably chosen laser pulses. As illustrations we demonstrate the feasibility of all optical ferromagnetic resonance and optical magnetization reorientation.Comment: 8 pages, 3 figure

Electron spin and charge switching in a coupled quantum dot quantum ring system

Few-electron systems confined in a quantum dot laterally coupled to a surrounding quantum ring in the presence of an external magnetic field are studied by exact diagonalization. The distribution of electrons between the dot and the ring is influenced by the relative strength of the dot and ring confinement, the gate voltage and the magnetic field which induces transitions of electrons between the two parts of the system. These transitions are accompanied by changes in the periodicity of the Aharonov-Bohm oscillations of the ground-state angular momentum. The singlet-triplet splitting for a two electron system with one electron confined in the dot and the other in the ring exhibits piecewise linear dependence on the external field due to the Aharonov-Bohm effect for the ring-confined electron, in contrast to smooth oscillatory dependence of the exchange energy for laterally coupled dots in the side-by-side geometry.Comment: to appear in PRB in August 200