arXiv subjects

Yoshiyuki Ono

Publications and source records attributed to Yoshiyuki Ono.

13 recordsLinked to original sources

arXiv2008

Conductance plateau transitions in quantum Hall wires with spatially correlated random magnetic fields

Quantum transport properties in quantum Hall wires in the presence of spatially correlated disordered magnetic fields are investigated numerically. It is found that the correlation drastically changes the transport properties associated with the edge state, in contrast to the naive expectation that the correlation simply reduces the effect of disorder. In the presence of correlation, the separation between the successive conductance plateau transitions becomes larger than the bulk Landau level separation determined by the mean value of the disordered magnetic fields. The transition energies coincide with the Landau levels in an effective magnetic field stronger than the mean value of the disordered magnetic field. For a long wire, the strength of this effective magnetic field is of the order of the maximum value of the magnetic fields in the system. It is shown that the effective field is determined by a part where the stronger magnetic field region connects both edges of the wire.

cond-mat.mes-hall↗

arXiv2008

Berry's phase in the multimode Peierls states

It is shown that Berry's phase associated with the adiabatic change of local variables in the Hamiltonian can be used to characterize the multimode Peierls state, which has been proposed as a new type of the ground state of the two-dimensional(2D) systems with the electron-lattice interaction.

cond-mat.stat-mech↗

arXiv2007

Unconventional conductance plateau transitions in quantum Hall wires with spatially correlated disorder

Quantum transport properties in quantum Hall wires in the presence of spatially correlated random potential are investigated numerically. It is found that the potential correlation reduces the localization length associated with the edge state, in contrast to the naive expectation that the potential correlation increases it. The effect appears as the sizable shift of quantized conductance plateaus in long wires, where the plateau transitions occur at energies much higher than the Landau band centers. The scale of the shift is of the order of the strength of the random potential and is insensitive to the strength of magnetic fields. Experimental implications are also discussed.

cond-mat.mes-hall↗

arXiv2005

Correlation Effect on the Two-Dimensional Peierls Phase

The effect of the electron-electron (e-e) interaction on the Peierls lattice distortions due to the electron-lattice (e-l) interaction is studied in the two-dimensional Peierls-Hubbard model, treating the fluctuation of e-e interaction around the Hartree-Fock solution within the 2nd order perturbation theory. In our previous work, using the Hartree-Fock approximation, we found multimode Peierls lattice distortions with wave vectors, the nesting vector $\mathbf{Q}$ and those parallel to it, are not affected by an e-e interaction if it is weak compared with the e-l coupling. The phase transition between the BOW (bond order wave) with multimode lattice distortions and the SDW (spin density wave) with the wave vector $\mathbf{Q}$ behaves as the 1st order transition. The property of the multimode BOW is found to change drastically when we consider the fluctuation effect within the 2nd order perturbation theory. The Fourier components of the multimode BOW increase gradually as the e-e interaction parameter is increased. Especially the Fourier component with the wave vector equal to the smallest reciprocal lattice vector in the presence of the multimode BOW is most strongly affected by the fluctuation effect.

cond-mat.str-el↗

arXiv2003

Multi-Modes Phonon Softening in Two-Dimensional Electron-Lattice System

Phonon dispersion in a two-dimensional electron-lattice system described by a two-dimensional square-lattice version of Su-Schrieffer-Heeger's model and having the half-filled electronic band is studied theoretically at temperatures higher than the mean field critical temperature of the Peierls transition. When the temperature is lowered from the higher region down to the critical one, softening of multi phonon modes which have wave vectors equal to the nesting vector $\vv{Q}=(π/a,π/a)$ with $a$ the lattice constant or parallel to $\vv{Q}$ is observed. Although both of the transverse and longitudinal modes are softened at the critical temperature in the case of the wave vector equal to $\vv{Q}$, only the transverse modes are softened for other wave vectors parallel to $\vv{Q}$. This behavior is consistent with the Peierls distortions at lower temperatures.

cond-mat.soft↗

arXiv2001

Degeneracy of Ground State in Two-dimensional Electron-Lattice System

We discuss the ground state of a two dimensional electron-lattice system described by a Su-Schrieffer-Heeger type Hamiltonian with a half-filled electronic band, for which it has been pointed out in the previous paper [J. Phys. Soc. Jpn. 69 (2000) 1769-1776] that the ground state distortion pattern is not unique in spite of a unique electronic energy spectrum and the same total energy. The necessary and sufficient conditions to be satisfied by the distortion patterns in the ground state are derived numerically. As a result the degrees of degeneracy in the ground state is estimated to be about $N^{N/4}$ for $N \gg 1$ with $N$ the linear dimension of the system.

cond-mat.mtrl-sci↗

arXiv2001

Peierls Distortion in Two-Dimensional Tight-Binding Model

The Peierls distortions in a two-dimensional electron-lattice system described by a Su-Schrieffer-Heeger type model extended to two-dimensions are numerically studied for a square lattice. The electronic band is just half-filled and the nesting vector is ($π/a$, $π/a$) with $a$ the lattice constant. In contrast to the previous understanding on the Peierls transition in two dimensions, the distortions which are determined so as to minimize the total energy of the system involve not only the Fourier component with the nesting wave vector but also many other components with wave vectors parallel to the nesting vector. It is found that such unusual distortions contribute to the formation of gap in the electronic energy spectrum by indirectly (in the sense of second order perturbation) connecting two states having wave vectors differing by the nesting vector from each other. Analyses for different system sizes and for different electron-lattice coupling constants indicate that the existence of such distortions is not a numerical artifact. It is shown that the gap of the electronic energy spectrum is finite everywhere over the Fermi surface.

cond-mat.mtrl-sci↗

arXiv1998

Transport in two dimensional periodic magnetic fields

Ballistic transport properties in a two dimensional electron gas are studied numerically, where magnetic fields are perpendicular to the plane of two dimensional electron systemsand periodically modulated both in $x$ and $y$ directions. We show that there are three types of trajectories of classical electron motions in this system; chaotic, pinned and runaway trajectories. It is found that the runaway trajectories can explain the peaks of magnetoresistance as a function of external magnetic fields, which is believed to be related to the commensurability effect between the classical cyclotron diameter and the period of magnetic modulation. The similarity with and difference from the results in the antidot lattice are discussed.

cond-mat.mes-hall↗

arXiv1998

Photogeneration Dynamics of a Soliton Pair in Polyacetylene

Dynamical process of the formation of a soliton pair from a photogenerated electron-hole pair in polyacetylene is studied numerically by adopting the SSH Hamiltonian. A weak local disorder is introduced in order to trigger the formation. Starting from an initial configuration with an electron at the bottom of the conduction band and a hole at the top of the valence band, separated by the Peierls gap, the time dependent Schr${\rm \ddot{o}}$ndinger equation for the electron wave functions and the equation of motion for the lattice displacements are solved numerically. After several uniform oscillations of the lattice system at the early stage, a large distortion corresponding to a pair of a soliton and an anti-soliton develops from a point which is determined by the location and type of the disorder. In some cases, two solitons run in opposite directions, leaving breather like oscillations behind, and in other cases they form a bound state emitting acoustic lattice vibrational modes.

cond-mat↗

arXiv1997

Novel Scaling Relation of the Energy Spacing Distribution in Quantum-Hall Systems

The shape analysis of the energy spacing distribution $P(s)$ obtained from numerical simulation of two dimensional disordered electron systems subject to strong magnetic fields is performed. In the present work we reanalyze the data obtained in a previous publication. Special moments of the $P(s)$ function related to Rényi-entropy differences show a novel scale invariant relation that is attributed to the presence of one-parameter scaling. This relation seems to show both deviations and universality depending on which Landau-band is considered and whether the disorder is correlated or uncorrelated. Furthermore, our analysis shows the existence of an huge, however, irrelevant length scale in the case of the second lowest Landau-band and no disorder correlations that completely disappears with the introduction of disorder correlations on the range of one magnetic length.

cond-mat.mes-hall↗

arXiv1997

Interchain Pair Hopping of Solitons and Polarons via Dopants in Polyacetylene

Interchain hopping of solitons and polarons in polyacetylene is studied by numerical simulation of their motion under an electric field. Use is made of the Su-Schrieffer-Heeger model supplemented with intrachain electron-electron interactions and dopant potentials. We find that charged solitons can hop to the opposite chain by forming bound pairs (bipolarons). For the case of polarons also, hopping in a pair is more favorable than single polaron hopping. Interchain hopping of a polaron pair is more efficient than that of a soliton pair.

cond-mat.mtrl-sci↗

arXiv1996

Semi-Phenomenological Analysis of Dynamics of Nonlinear Excitations in One-Dimensional Electron-Phonon System

The structure of moving nonlinear excitations in one-dimensional electron-phonon systems is studied semi-phenomenologically by using an effective action in which the width of the nonlinear excitation is treated as a dynamical variable. The effective action can be derived from Su, Schrieffer and Heeger's model or its continuum version proposed by Takayama, Lin-Liu and Maki with an assumption that the nonlinear excitation moves uniformly without any deformation except the change of its width. The form of the action is essentially the same as that discussed by Bishop and coworkers in studying the dynamics of the soliton in polyacetylene, though some details are different. For the moving excitation with a velocity $v$, the width is determined by minimizing the effective action. A requirement that there must be a minimum in the action as a function of its width provides a maximum velocity. The velocity dependence of the width and energy can be determined. The motions of a soliton in p olyacetylene and an acoustic polaron in polydiacetylene are studied within this formulation. The obtained results are in good agreement with those of numerical simulations.

cond-mat↗

arXiv1995

Critical Level Statistics in Two-dimensional Disordered Electron Systems

The level statistics in the two dimensional disordered electron systems in magnetic fields (unitary ensemble) or in the presence of strong spin-orbit scattering (symplectic ensemble) are investigated at the Anderson transition points. The level spacing distribution functions $P(s)$'s are found to be independent of the system size or of the type of the potential distribution, suggesting the universality. They behave as $s^2$ in the small $s$ region in the former case, while $s^4$ rise is seen in the latter.

cond-mat↗