Avoiding the polarization catastrophe in LaAlO3 overlayers on SrTiO3(001) through a polar distortion

A pronounced uniform polar distortion extending over several unit cells enables thin LaAlO3 overlayers on SrTiO3(001) to counteract the charge dipole and thereby neutralize the "polarization catastrophe" that is suggested by simple ion-counting. This unanticipated mechanism, obtained from density functional theory calculations, allows several unit cells of the LaAlO3 overlayer to remain insulating (hence, fully ionic). The band gap of the system, defined by occupied O $2p$ states at the surface and unoccupied Ti 3d states at the interface in some cases $\sim$20 \AA distant, decreases with increasing thickness of the LaAlO3-film before an insulator-to-metal transition and a crossover to an electronic reconstruction occurs at around five monolayers of LaAlO3.Comment: 5 pages, 4 figures, submitted for publicatio

Ferroelectric Dead Layer Driven by a Polar Interface

Based on first-principles and model calculations we investigate the effect of polar interfaces on the ferroelectric stability of thin-film ferroelectrics. As a representative model, we consider a TiO2-terminated BaTiO3 film with LaO monolayers at the two interfaces that serve as doping layers. We find that the polar interfaces create an intrinsic electric field that is screened by the electron charge leaking into the BaTiO3 layer. The amount of the leaking charge is controlled by the boundary conditions which are different for three heterostructures considered, namely Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and SrRuO3/LaO/BaTiO3/LaO. The intrinsic electric field forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. Our first-principles and model calculations demonstrate that the effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric. The predicted mechanism for a ferroelectric dead layer at the interface controls the critical thickness for ferroelectricity in systems with polar interfaces.Comment: 33 Pages, 5 figure

Treatment Considerations for Mandibulectomy Patients

Prosthetic rehabilitation of patients after resection of the mandible due to operation of malignant tumors usually poses a great problem. Loss of tissues and damage caused by radiotherapy cause various functional deficiencies and dysfunction in the stomatognathic system. The study concerned treatment of a group of mandibulectomy patients with problems related mainly to restoration of jaw relationship, lack of occlusion and dysfunctions. In the escamined cases immediate or delayed reconstructive surgery had been completed before prosthetics to treat mandibular discontinuity defects. Unfortunately, many of the patients exibit lack of occlusion, mandibular deviations and torque due to incorrect muscle activity. Prosthetic management was part of a multidisciplinary approach to the problem. Treatment included myotherapy, gradual occlusal rearrangement with the use of therapeutic and corrective splints, special appliances and prostheses with leading inclined planes and guiding surfaces. The degree of success was related to the location and extent of the mandibular resection, the shape of the bone transplants and presence or absence of natural teeth. The aims of treatment realised were the restoration of acceptable occlusion and improved functional efficiency of the masticatory system

Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO3_3/SrTiO3_3 Interfaces

A two dimensional electronic system with novel electronic properties forms at the interface between the insulators LaAlO$_3$ and SrTiO$_3$. Samples fabricated until now have been found to be either magnetic or superconducting, depending on growth conditions. We combine transport measurements with high-resolution magnetic torque magnetometry and report here evidence of magnetic ordering of the two-dimensional electron liquid at the interface. The magnetic ordering exists from well below the superconducting transition to up to 200 K, and is characterized by an in-plane magnetic moment. Our results suggest that there is either phase separation or coexistence between magnetic and superconducting states. The coexistence scenario would point to an unconventional superconducting phase in the ground state.Comment: 10 pages, 4 figure

Stochastic multiple mapping conditioning for a piloted, turbulent jet diffusion flame

A stochastic implementation of the multiple mapping conditioning (MMC) approach has been applied to a turbulent jet diffusion flame (Sandia Flame D). This implementation combines the advantages of the basic concepts of a mapping closure methodology with a probability density approach. A single reference variable has been chosen. Its evolution is described by a Markov process and then mapped to the mixture fraction space. Scalar micro-mixing is modelled by a modified “interaction by exchange with the mean” (IEM) mixing model where the particles mix with their -in reference space- conditionally averaged means. The formulation of the closure leads to localness of mixing in mixture fraction space and consequently improved localness in composition space. Results for mixture fraction and reactive species are in good agreement with the experimental data. The MMC methodology allows for the introduction of an additional “minor dissipation time scale” that controls the fluctuations around the conditional mean. A sensitivity analysis based on the conditional temperature fluctuations as a function of this time scale does not endorse earlier estimates for its modelling, but only relatively large dissipation time scales of the order of the integral turbulence time scale yield acceptable levels of conditional fluctuations that agree with experiments. With the choice of a suitable dissipation time scale, MMC-IEM thus provides a simple mixing model that is capable of capturing extinction phenomena, and it gives improved predictions over conventional PDF predictions using simple IEM mixing models

Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO3) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO3 matrix. Such correlation effects can lead to new functionalities in designed heterostructures