Index of content:
Volume 29, Issue 1, January 2003
- LOW-DIMENSIONAL AND DISORDERED SYSTEMS
29(2003); http://dx.doi.org/10.1063/1.1542377View Description Hide Description
The conductance of disordered electron systems of finite size is calculated by reducing the initial dynamical problem of arbitrary dimensionality to strictly one-dimensional problems for single-particle mode propagators. It is shown that the metallic ground state of two-dimensional conductors, considered as a limiting case of three-dimensional quantum waveguides, is due to their multimode nature. As the thickness of the waveguide is decreased, e.g., with the aid of a “pressing” potential, the electron system undergoes a sequence of continuous quantum phase transitions involving a discrete change in the number of extended modes. The closing of the last current-carrying mode is interpreted as a phase transition of the electron system from the metallic to an insulator state. The results agree qualitatively with the observed “anomalies” of the resistance of various two-dimensional electron and hole systems.
Mechanism of vortex switching in magnetic nanodots under a circular magnetic field. II. Dynamics of a spin plaquette containing a vortex29(2003); http://dx.doi.org/10.1063/1.1542378View Description Hide Description
For a theoretical explanation of the mechanism of switching of the polarization of magnetic vortices in an external circular magnetic field, a small spin plaquette in a vortex configuration is considered. An analytical investigation of the initial (linear) stage of the vortex switching process is carried out. The analytical results obtained confirm the data of a numerical calculation of the plaquette dynamics. Both the numerical simulation and an analytical treatment of the initial stage of activation show the importance of taking the azimuthal modes of the system into account. It is at the frequencies of these modes that the most rapid growth of the vortex energy and the total intraplane projection of the magnetization occur. Increasing the amplitude of these modes leads to parametric excitation of a low-frequency symmetric mode, and that causes vortex switching. The results provide a qualitative explanation of the data of a numerical simulation of vortex switching in large magnetic systems and can be used in experiments on the directed influencing of the polarization of vortices in magnetic nanodots.
29(2003); http://dx.doi.org/10.1063/1.1542379View Description Hide Description
A solution of the problem of magnon scattering on Belavin–Polyakov solitons in two-dimensional magnets is constructed in the framework of a generalized σ model. This model can serve as a basis for describing both ferromagnets and antiferromagnets, and it can also describe ferrimagnets near the point of compensation of the sublattice spins. The problem of magnon scattering on a soliton is formulated‘ for this model, and its exact solution is obtained for a partial mode with azimuthal quantum number It is shown that in a linear approximation this mode completely describes the dynamics of the center of the soliton in a magnet of finite size. Effective equations of motion for solitons in different magnets are constructed on the basis of this analysis.