International Journal of Modern Physics B

We present a systematic construction of effective Lagrangians for the low energy and momentum region of ferromagnetic and antiferromagnetic spin waves in crystalline solids. We fully exploit the spontaneous symmetry breaking pattern SU(2)→U(1), the fact that spin waves are its associated Goldstone modes, the crystallographic space group and time reversal symmetries. We show how to include explicit SU(2) breaking terms due to spin-orbit and magnetic dipole interactions. The coupling to electromagnetic fields is also discussed in detail. For definiteness we work with the space group and present our results to next to leading order.

Dynamical coherent structure (pattern) formation in the Klein–Gordon lattice excited by periodic external field near the optical resonance is studied. It is shown that the patterns involve spatial or spatio-temporal modulation of particles vibration amplitude in the lattice and can be generated in rather broad region of excitation parameters. An influence of cubic anharmonicity in the lattice potential and that of random noise on the pattern formation is examined.

We study, using numerical exact diagonalisation, some static and dynamical properties of a single impurity substituted into a one-dimensional repulsive Hubbard chain. A systematic scan of the parameter-space reveals a rich magnetic phase diagram. Interactions on the lattice stabilize the local moment phase of the impurity. A scalar impurity is seen to induce local moments on the neighbouring sites near Half Filling. Static spin and charge correlation functions reflect a non-Fermi liquid character of the ground state in the presence of a scalar impurity.

The spectrum and damping of collective excitations of a system of electric dipole centers with internal degrees of freedom in glass are calculated. It is shown that one of the collective modes becomes soft, signaling a spin-glass like phase transition in insulating glass. The contribution to the specific heat is determined. The possibility of phase transition from paraelectric to electric pseudospin glass phase in dielectric glass is considered.

Vanadium nitride thin films have been deposited on to quartz substrates by dc magnetron sputtering at two different total pressures and a series of nitrogen partial pressures. The spectral transmittance of these films, in the region 350 to 1500 nm, is strongly dependent on the nitrogen partial pressure during sputtering and relatively insensitive to total pressure. The films became more transparent as the nitrogen partial pressure was decreased at a constant total pressure. The optical constants, refractive index and extinction coefficient, exhibited a similar dependence on the nitrogen partial pressure. The sheet resistivity of the films decreased with increasing nitrogen partial pressure. The values of resistivity indicate that the films are semiconducting rather than metalic.

Recently, the structural stability of the high temperature structural intermetallic Ti₃Al has been investigated experimentally and a transition from the DO₁₉ to the DO₂₄ structure has been reported. We have performed band structure calculations as a function of reduced volume by tight binding linear muffin-tin orbital (TBLMTO) method to look into these transitions to understand their mechanisms in terms of its electronic structure. The mechanism of the DO₁₉ to the DO₂₄ structure is understood to be due to shifting of the Fermi energy into a valley in the density of states curve, thereby driving the system to a more stable structure.

In this paper, we construct a Hamiltonian of the impurity model with next-nearest-neighbor interaction within the framework of the open boundary Heisenberg XYZ spin chain. This impurity model is an exactly solved one and it degenerates to the integrable XXZ impurity model under the triangular limit. It is the first approach to add the impurities and next-nearest-neighbor interaction to the integrable completely anisotropic Heisenberg spin chain. We find also that the impurity parameters in the bulk are real when the cross parameter is imaginary for the Hermitian Hamiltonian, or vice versa, when the next-nearest-neighbor interaction is introduced. The eigenvalue of the Hamiltonian and the Bethe ansatz equations for the trigonometric limit case are derived also.