arXiv subjects

V. A. Geyler

Publications and source records attributed to V. A. Geyler.

11 recordsLinked to original sources

arXiv2006

Spectrum structure for a three-dimensional periodic array of quantum dots in a uniform magnetic field

By means of the operator extension theory, we construct an explicitly solvable model of a simple-cubic three-dimensional regimented array of quantum dots in the presence of a uniform magnetic field. The spectral properties of the model are studied. It is proved that for each magnetic flux the band is the image of the spectrum of the tight-binding operator under an analytical transformation. In the case of rational magnetic flux the spectrum is described analytically. The flux-energy and angle-energy diagrams are obtained numerically.

cond-mat.mes-hall↗

arXiv2005

Zero modes in a system of Aharonov--Bohm solenoids on the Lobachevsky plane

We consider a spin 1/2 charged particle on the Lobachevsky plane subjected to a magnetic field corresponding to a discrete system of Aharonov-Bohm solenoids. Let $H^+$ and $H^-$ be the two components of the Pauli operator for spin up and down, respectively. We show that neither $H^+$ nor $H^-$ has a zero mode if the number of solenoids is finite. On the other hand, a construction is described of an infinite periodic system of solenoids for which either $H^+$ or $H^-$ has zero modes depending on the value of the flux carried by the solenoids.

math-ph↗

arXiv2004

Zero modes in a system of Aharonov-Bohm fluxes

We study zero modes of two-dimensional Pauli operators with Aharonov--Bohm fluxes in the case when the solenoids are arranged in periodic structures like chains or lattices. We also consider perturbations to such periodic systems which may be infinite and irregular but they are always supposed to be sufficiently scarce.

math-ph↗

arXiv2004

Geometrical phase for a three-dimensional anisotropic quantum well

A three-dimensional anisotropic quantum well placed in an adiabatically precessing uniform magnetic field is considered and an explicit formula for the Berry phase is obtained. To get the Berry phase, a purely algebraic algorithm of reducing a quadratic Hamiltonian to the canonical form via symplectic transformations of the phase space is presented.

cond-mat.mes-hall↗

arXiv2003

On the Pauli operator for the Aharonov-Bohm effect with two solenoids

We consider a spin-1/2 charged particle in the plane under the influence of two idealized Aharonov-Bohm fluxes. We show that the Pauli operator as a differential operator is defined by appropriate boundary conditions at the two vortices. Further we explicitly construct a basis in the deficiency subspaces of the symmetric operator obtained by restricting the domain to functions with supports separated from the vortices. This construction makes it possible to apply the Krein's formula to the Pauli operator.

math-ph↗

arXiv2003

Effect of the surface curvature on the magnetic moment and persistent currents in two-dimensional quantum rings and dots

The effect of the surface curvature on the magnetic moment and persistent currents in two-dimensional (2D) quantum rings and dots is investigated. It is shown that the surface curvature decreases the spacing between neighboring maxima of de Haas -- van Alphen (dHvA) type oscillations of the magnetic moment of a ring and decreases the amplitude and period of Aharonov -- Bohm (AB) type oscillations. In the case of a quantum dot, the surface curvature reduces the level degeneracy at zero magnetic fields. This leads to a suppression of the magnetic moment at low magnetic fields. The relation between the persistent current and the magnetic moment is studied. We show that the surface curvature decreases the amplitude and the period of persistent current oscillations.

cond-mat.mes-hall↗

arXiv2003

Spectral diagrams of Hofstadter type for the Bloch electron in three dimensions

Flux-energy and angle-energy diagrams for an exact three-dimensional Hamiltonian of the Bloch electron in a uniform magnetic field are analyzed. The dependence of the structure of the diagrams on the direction of the field, the geometry of the Bravais lattice and the number of atoms in an elementary cell is considered. Numerical evidence is given that the angle-energy diagram may have a fractal structure even in the case of a cubic lattice. It is shown that neglecting coupling of Landau bands changes considerably the shape of the diagrams.

cond-mat.mes-hall↗

arXiv2003

Quantum Hall effect on the Lobachevsky plane

The Hall conductivity of an electron gas on the surface of constant negative curvature (the Lobachevsky plane) in the presence of an orthogonal magnetic field is investigated. It is shown that the effect of the surface curvature is to change the break locations and the plateau widths in the Hall conductivity. An increase of temperature results in smearing of the steps.

cond-mat.mes-hall↗

arXiv2002

Large gaps in point-coupled periodic systems of manifolds

We study a free quantum motion on periodically structured manifolds composed of elementary two-dimensional "cells" connected either by linear segments or through points where the two cells touch. The general theory is illustrated with numerous examples in which the elementary components are spherical surfaces arranged into chains in a straight or zigzag way, or two-dimensional square-lattice "carpets". We show that the spectra of such systems have an infinite number of gaps and that the latter dominate the spectrum at high energies.

math-ph↗

arXiv2002

The geometric structure of the Landau bands

We have proposed a semiclassical explanation of the geometric structure of the spectrum for the two-dimensional Landau Hamiltonian with a two-periodic electric field without any additional assumptions on the potential. Applying an iterative averaging procedure we approximately, with any degree of accuracy, separate variables and describe a given Landau band as the spectrum of a Harper-like operator. The quantized Reeb graph for such an operator is used to obtain the following structure of the Landau band: localized states on the band wings and extended states near the middle of the band. Our approach also shows that different Landau bands have different geometric structure.

cond-mat.mes-hall↗

arXiv2000

Geometric phase related to point-interaction transport on a magnetic Lobachevsky plane

We consider a charged quantum particle living in the Lobachevsky plane and interacting with a homogeneous magnetic field perpendicular to the plane and a point interaction which is transported adiabatically along a closed loop C in the plane. We show that the bound-state eigenfunction acquires at that the Berry phase equal to 2πtimes the number of the flux quanta through the area encircled by C.

math-ph↗