Modern Physics Letters B

ESR measurements have been carried out for La_0.97Ca_0.03MnO₃ at temperatures from 4 K up to 760 K. below ≃243 K, two kinds of spectra, the high-field and low-field signals, are observed down to 96 and 4 K, respectively. They are assumed to be due to Mn⁴⁺ and Mn³⁺ ions, respectively. From the g-shifts of the high-field (Mn⁴⁺) signals, the magnetic interaction coefficient between Mn⁴⁺ and Mn³⁺ spins is estimated. Clear single ESR was observed above ≃255 K, and its linewidth and intensity are obtained as a function of temperature. The linewidth nearly follows exp(-550/T), and the intensity gradually deviates from Curie's law below ≃550 K, presumably due to the spin-cluster formation.

Magnetic measurements are reported on YBCO thin films (d<500 nm) in the perpendicular geometry, H‖c. By analyzing the sweep rate dependence of the magnetization for temperatures 35 ≤ T ≤ 77 K and H≤10 kOe, we find that the moment has a power law dependence on the sweep rate. This dependence is indicative of power law E(J) characteristics for these thin films and from this a logarithmic current dependence of the activation potential U(J) is inferred. We find that our magnetic relaxation measurements are also consistent with the logarithmic U(J) dependence obtained from the sweep rate measurements. Activation barriers for flux creep are determined for various temperatures and their field dependence is discussed.

We define a generalized rate equation for an observable in quantum mechanics, that involves a parameter q and whose limit q→1 gives the standard Heisenberg equation. The generalized rate equation is used to study dynamics of current-biased Josephson junction. It is observed that this toy model incorporates diffraction-like effects in the critical current. Physical interpretation for q is provided which is also shown to be a q-deformation parameter.

By noticing that although single-mode Susskind–Glogower phase operator does not commute with photon number operator, two-mode nonlinear phase operator commutes with number-difference operator. We reveal that the common eigenstate <η| of two-particles' relative coordinate and total momentum involves the entanglement between phase and amplitude. We also reveal entanglement between number difference and amplitude inherent in the state |D,|η|>, where is a deductive state of |η>.

Applying the minimal path approximation to the Langevin equation, we revisit the well-known Kramers problem, noise-activated escape of a particle out of a meta-stable well and present a new technique to evaluate the activation rate. This new technique is valid for low to intermediate friction and is accurate for low temperatures. For low friction, analytical solution is derived. For intermediate friction, numerical results are obtained with minimal computational effort and the numerical effort required does not increase going for lower temperature.

The growth kinetics of a system with spin-exchange dynamics has been investigated by means of computer simulations. These systems are used to simulate diffusive processes and kinetic phenomena far away from equilibrium. As a measure of growth we have studied the mean square displacement <R²> of tagged particles. It is found that <R²>t^1-n follows a sublinear time dependence, which is explained in terms of the changes of the distribution of atoms between sites within the ordered region and sites of the domain boundaries. The time-dependence of the diffusion coefficient has been derived. The analogies to the relaxation in disordered systems, such as in a:Si–H and in O/W(110), is discussed.

The weak-localization correction to the conductivity for a quasi-two-dimensional disordered electron system is calculated in the presence of magnetic impurity scatterings. The analytical result is obtained as a function of the magnetic scattering time, and the interesting magnetic-scattering-dependent crossover behavior from 3D to 2D is discussed.

We study the effect of temperature on Intrinsic Localized Modes (ILM) in anharmonic lattices. An approach is proposed based on the Method of the Unsymmetrized Self-Consistent Field (USF). The special case of an odd-parity mode in an anharmonic linear chain with Mie–Lennard–Jones potential is investigated in more detail. We find that in the weak anharmonic approximation, an increasing of temperature does not change the pattern of the mode, leading to a very small decreasing of the displacement amplitudes and a decreasing of the mode frequency. The frequency of the mode increases with increasing of both the repulsion and attraction indexes. This effect is more sensitive to the repulsion index.