乾 徳夫

Abstract The temporal variation of the electric current induced by an oscillating Peierls phase in a ring-shaped system is studied using a tight-binding model with the Peierls substitution. For a single electron current, when the initial wavefunction is a traveling wave with a constant wave number, the time-averaged current does not depend on the oscillation frequency of Peierls phase, in contrast to conventional electrical induction. However, when the initial state is a superposition of degenerate eigenstates, the mean square current between nearest-neighbor sites depends on both the initial amplitudes of the clockwise and counterclockwise traveling waves and the oscillation frequency. Moreover, the total current, defined as the sum of currents between nearest-neighbor sites and determines the induced magnetic field, depends on the amplitudes of the superposition but remains independent of the oscillation frequency.

Abstract The time-averaged orbital angular momentum of an oscillator coupled to single- and dual-frequency electromagnetic waves is investigated by exactly solving the Heisenberg equation of motion. An applied magnetic field splits the natural frequency of the oscillator into distinct resonances in the presence of a single-frequency wave. When the magnetic interaction is much stronger than the dipole interaction, the angular momentum reaches extreme values near the lower and upper split frequencies. For dual frequencies, if the two frequencies are widely separated, the angular momentum is approximately a superposition of the single-frequency cases. Consequently, the total angular momentum is represented as the sum of contributions from the lower and higher frequencies in strong magnetic fields. However, significant deviations from this superposition occur when the oscillator interacts with closely spaced frequencies.

Abstract Temporal variations in electric currents along a ring, induced by a time-dependent magnetic flux are examined using the tight-binding model. When all nearest-neighbor atom pairs share the same transfer integral and the Peierls phase changes linearly with time, the resulting electric current remains uniform and matches the magnitude of the current induced by a static magnetic field producing the same Peierls phase. However, in the presence of disorder, where transfer integrals differ, the electric current becomes position-dependent. For a randomly disordered ring with the transfer integrals following a normal distribution, an increase in the standard deviation reduces the mean electric current under a static magnetic field. In contrast, when exposed to a time-varying magnetic field, the induced currents in the disordered ring can increase as the standard deviation increases.