Phenomenological theory of phase transitions in epitaxial BaxSr(1-x)TiO3 thin films

A phenomenological thermodynamic theory of BaxSr(1-x)TiO3 (BST-x) thin films epitaxially grown on cubic substrates is developed using the Landau-Devonshire approach. The eighth-order thermodynamic potential for BT single crystal and modified fourth-order potential for ST single crystal were used as starting potentials for the end-members of the solid solution with the aim to develop potential of BST-$x$ solid solution valid at high temperatures. Several coefficients of these potentials for BT were changed to obtain reasonable agreement between theory and experimental phase diagram for BST-x (x > 0.2) solid solutions. For low Ba content we constructed the specific phase diagram where five phases converge at the multiphase point (T_N2 = 47 K, x = 0.028) and all transitions are of the second order. The "concentration-misfit strain" phase diagrams for BST-x thin films at room temperature and "temperature-misfit strain" phase diagrams for particular concentrations are constructed and discussed. Near T_N2 coupling between polarization and structural order parameter in the epitaxial film is modified considerably and large number of new phases not present in the bulk materials appear on the phase diagram.Comment: 8 pages 5 figure

Computation of Composition Functions and Invariant Vector Fields in Terms of Structure Constants of Associated Lie Algebras

Methods of construction of the composition function, left- and right-invariant vector fields and differential 1-forms of a Lie group from the structure constants of the associated Lie algebra are proposed. It is shown that in the second canonical coordinates these problems are reduced to the matrix inversions and matrix exponentiations, and the composition function can be represented in quadratures. Moreover, it is proven that the transition function from the first canonical coordinates to the second canonical coordinates can be found by quadratures

Deuteron-equivalent and phase-equivalent interactions within light nuclei

Background: Phase-equivalent transformations (PETs) are well-known in quantum scattering and inverse scattering theory. PETs do not affect scattering phase shifts and bound state energies of two-body system but are conventionally supposed to modify two-body bound state observables such as the rms radius and electromagnetic moments. Purpose: In order to preserve all bound state observables, we propose a new particular case of PETs, a deuteron-equivalent transformation (DET-PET), which leaves unchanged not only scattering phase shifts and bound state (deuteron) binding energy but also the bound state wave function. Methods: The construction of DET-PET is discussed; equations defining the simplest DET-PETs are derived. We apply these simplest DET-PETs to the JISP16 $NN$ interaction and use the transformed $NN$ interactions in calculations of $^3$H and $^4$He binding energies in the No-core Full Configuration (NCFC) approach based on extrapolations of the No-core Shell Model (NCSM) basis space results to the infinite basis space. Results: We demonstrate the DET-PET modification of the $np$ scattering wave functions and study the DET-PET manifestation in the binding energies of $^3$H and $^4$He nuclei and their correlation (Tjon line). Conclusions: It is shown that some DET-PETs generate modifications of the central component while the others modify the tensor component of the $NN$ interaction. DET-PETs are able to modify significantly the $np$ scattering wave functions and hence the off-shell properties of the $NN$ interaction. DET-PETs give rise to significant changes in the binding energies of $^3$H (in the range of approximately 1.5 MeV) and $^4$He (in the range of more than 9 MeV) and are able to modify the correlation patterns of binding energies of these nuclei

NN Interaction JISP16: Current Status and Prospect

We discuss realistic nonlocal NN interactions of a new type - J-matrix Inverse Scattering Potential (JISP). In an ab exitu approach, these interactions are fitted to not only two-nucleon data (NN scattering data and deuteron properties) but also to the properties of light nuclei without referring to three-nucleon forces. We discuss recent progress with the ab initio No-core Shell Model (NCSM) approach and respective progress in developing ab exitu JISP-type NN-interactions together with plans of their forthcoming improvements.Comment: 9 pages, 3 figures, to be published in Proceedings of Few-body 19 conferenc