arXiv subjects

Yousef Yousefi

Publications and source records attributed to Yousef Yousefi.

7 recordsLinked to original sources

arXiv2015

Quadrupole Excitation in Tunnel Splitting Oscillation in Nano-Particle $Mn_{12}$

We analyze the interference between tunneling paths that occurs for a spin system with special Hamiltonian both for dipole and quadrupole excitation. Using an instanton approach, we find that as the strength of the second-order transverse anisotropy is increased, the tunnel splitting for both excitations are modulated, with zeros occurring periodically and the number of quenching points for quadrupole excitation decreases. This effect results from the interference of four tunneling paths connecting easy-axis spin orientations and occurs in the absence of any magnetic field.

cond-mat.other↗

arXiv2015

Magnetic Solitons for Non Heisenberg Anisotropic Hamiltonians in Linear Quadrupole Excitations

We discuss system with non-isotropic non-Heisenberg Hamiltonian with nearest neighbor exchange within a mean field approximation process. We drive equations describing non-Heisenberg non-isotropic model using coherent states in real parameters and then obtain dispersion equations of spin wave of dipole and quadrupole branches for a small linear excitation from the ground state. In final, soliton solution for quadrupole branches for these linear equations obtained.

cond-mat.other↗

arXiv2013

Semi classical modeling of isotropic Non-Heisenberg magnets for spin S=1 and linear quadrupole excitation dynamics

In this paper, equations describing one-dimensional Non-Heisenberg model are studied by use of generalized coherent states in real parameterization and then dissipative spin wave equation for dipole and quadrupole branches is obtained if there is a small linear excitation from the ground state. Finally, it is shown that for such exchange-isotropy Hamiltonians, optical branch of spin wave is non-dissipative.

cond-mat.str-el↗

arXiv2012

A Simple Classification of Solitons

In this report, fundamental educational concepts of linear and non-linear equations and solutions of nonlinear equations from the book High-Temperature Superconductivity: The Nonlinear Mechanism and Tunneling Measurements (Kluwer Academic Publishers, Dordrecht, 2002, pages 101-142) is given. There are a few ways to classify solitons. For example, there are topological and nontopological solitons. Independently of the topological nature of solitons, all solitons can be divided into two groups by taking into account their profiles: permanent and timedependent. For example, kink solitons have a permanent profile (in ideal systems), while all breathers have an internal dynamics, even, if they are static. So, their shape oscillates in time. The third way to classify the solitons is in accordance with nonlinear equations which describe their evolution. Here we discuss common properties of solitons on the basis of the four classification.

math-ph↗

arXiv2012

Semiclassical description of anisotropic magnets for spin S=1

In this paper, nonlinear equations describing one-dimensional non-Heisenberg ferromagnetic model are studied by use of generalized coherent states in a real parameterization. Also dissipative spin wave equation for dipole and quadruple branches is obtained if there is a small linear excitation from the ground state.

cond-mat.str-el↗

arXiv2011

Berry phase for coherent states in spin systems

In this paper we obtain Berry phase from Schrödinger equation. For vector states, basic kets are coherent states in real parameterization. We calculate Berry phase for spin S=1/2 and spin S=1 in SU(2) group and Berry phase for spin S=1 in SU(3) group.

math-ph↗

arXiv2011

Coherent states in real parameterization up to SU(5) and classical dynamics of spin systems

In this paper, we develop the formulation of the spin coherent state in real parameterization up to SU(5). The path integral in this representation of coherent state and its classical consequence are investigated. Using the resolution of unity of the coherent state, we derive a path integral expression for transition amplitude and in the classical limit we derive the classical equation of motion.

math-ph↗