Ab initio many-body calculations of static dipole polarizabilities of linear carbon chains and chain-like boron clusters

In this paper we report a theoretical study of the static dipole polarizability of two one-dimensional structures: (a) linear carbon chains C$_{n} (n=2-10)$ and (b) ladder-like planar boron chains B$_{n} (n=4-14)$. The polarizabilities of these chains are calculated both at the Hartree-Fock and the correlated level by applying accurate ab initio quantum chemical methods. Methods such as restricted Hartree-Fock, multi-configuration self-consistent field, multi-reference configuration-interaction method, M{\o}ller-Plesset second-order perturbation theory, and coupled-cluster singles, doubles and triples level of theory were employed. Results obtained from ab initio wave-function-based methods are compared with the ones obtained from the density-functional theory. For the clusters studied, directionally averaged polarizability per atom for both the systems is seen to increase with the chain size.Comment: 9 pages, 3 figures (included

The laminar-turbulent transition in a fibre laser

Studying the transition from a linearly stable coherent laminar state to a highly disordered state of turbulence is conceptually and technically challenging, and of great interest because all pipe and channel flows are of that type. In optics, understanding how a system loses coherence, as spatial size or the strength of excitation increases, is a fundamental problem of practical importance. Here, we report our studies of a fibre laser that operates in both laminar and turbulent regimes. We show that the laminar phase is analogous to a one-dimensional coherent condensate and the onset of turbulence is due to the loss of spatial coherence. Our investigations suggest that the laminar-turbulent transition in the laser is due to condensate destruction by clustering dark and grey solitons. This finding could prove valuable for the design of coherent optical devices as well as systems operating far from thermodynamic equilibrium

Comprehensive Studies of Magnetic Properties of Metal-Organic Frameworks and Molecular Compounds

Single-ion magnets (SIMs) are at the forefront of molecular electronic spin magnets with potential applications in magnetic memory storage devices. However, the magnetic properties of the SIMs are yet to be completely understood, especially the magnetic properties of large anisotropy systems. A part of this dissertation is to utilize optical and neutron spectroscopies such as far-IR magneto-spectroscopy (FIRMS) and inelastic neutron scattering (INS) to quantify the anisotropy and study the phonon properties of the SIMs as two-dimensional (2-D) metal-organic frameworks (MOFs) or coordination polymer (CP), and a molecular magnet. In addition, ab initio calculations are used to understand the origin of the anisotropy and the electronic structure of the systems. Furthermore, the systems studied in this dissertation can also be quantum bit (qubit) candidates. Qubits are the building blocks of quantum computers. The properties of qubits can be determined using pulsed electron paramagnetic resonance (pulsed EPR). The results yielded the spin-lattice relaxation time and the spin-spin relaxation time, where both relaxation times are crucial in determining the effectiveness of the qubit candidates. The second part of this dissertation focuses on studying the symmetry-protected topological states of a Haldane one-dimensional (1-D) spin-1 chain as a 2-D MOF. The topological properties of the Haldane spin-1 chain can be highlighted by the Haldane energy gap that exists between the non-magnetic singlet ground state and the triplet excited state, the fractionalized edge states, and the system’s robustness to external perturbations through symmetry-protection. Optical and neutron spectroscopies in addition to the magnetic susceptibility measurements were used to quantify the energy gaps as well as the anisotropy that governs the system. Furthermore, the spin chain is found to exhibit a critical field and critical temperature where the system observes a phase transition. These studies in this dissertation, in part, aim to give a complete understanding of the magnetic anisotropy and phonon properties of the SIM and qubit systems as well as to have a comprehensive understanding of the topological properties of the Haldane 1-D spin-1 chain system

Phase-field-crystal models for condensed matter dynamics on atomic length and diffusive time scales: an overview

Here, we review the basic concepts and applications of the phase-field-crystal (PFC) method, which is one of the latest simulation methodologies in materials science for problems, where atomic- and microscales are tightly coupled. The PFC method operates on atomic length and diffusive time scales, and thus constitutes a computationally efficient alternative to molecular simulation methods. Its intense development in materials science started fairly recently following the work by Elder et al. [Phys. Rev. Lett. 88 (2002), p. 245701]. Since these initial studies, dynamical density functional theory and thermodynamic concepts have been linked to the PFC approach to serve as further theoretical fundaments for the latter. In this review, we summarize these methodological development steps as well as the most important applications of the PFC method with a special focus on the interaction of development steps taken in hard and soft matter physics, respectively. Doing so, we hope to present today's state of the art in PFC modelling as well as the potential, which might still arise from this method in physics and materials science in the nearby future.Comment: 95 pages, 48 figure

Biasing Effects in Ferroic Materials

In this chapter we present an overview of some important concepts related to the processes and microstructural mechanisms that produce the deformation of hysteresis loops and the loss of their symmetry characteristics in ferroelectric, ferroelastic and ferromagnetic systems. The most discussed themes include: aging and fatigue as primary mechanisms of biased hysteresis loops in ferroelectric/ferroelastic materials, imprint phenomenon as an important biasing process in ferroelectric thin films, the development of an exchange bias field and of specific spin states, such as spin canting and spin-glass-like phases, as the main causes of biased hysteresis loops in different types of magnetic heterostructures. The present discussion leads to the identification of the main differences and possible analogies in the underlying mechanisms of possible biasing effects occurring in the different ferroic systems, which can benefit the theoretical description, modelling, and engineering of multifunctional devices based on ferroic systems experiencing the internal bias phenomena

ICCG-10: Tenth International Conference on Crystal Growth. Poster presentation abstracts

Poster presentation abstracts from the tenth International Conference on Crystal Growth (ICCG) (Aug. 16-21, 1992) are provided. Topics discussed at the conference include crystal growth mechanisms, superconductors, semiconductors, laser materials, optical materials, and biomaterials. Organizing committees, ICCG advisory board and officers, and sponsors of the conference are also included