M. I. Tsindlekht

High-frequency vortex dynamics in

We present a phenomenological description of the high-frequency vortex dynamics in and discuss the main parameters related to vortex motion, namely the viscous drag coefficient , the pinning constant (Labusch parameter) and the depinning frequency . We demonstrate experimental results on the angular and temperature dependence of , and in and compare these results with existing models. We show how studies of the vortex viscosity may yield information on the superclean limit. This limit corresponds to the formation of the discrete excitation spectrum in the vortex core due to quantum confinement and small coherence length. From the low-temperature viscosity data we conclude that the superclean limit in is reached for magnetic field perpendicular to the c-axis.

Frequency modulation of the superconducting parallel‐plate microwave resonator by laser irradiation

We have studied the effect of chopped laser irradiation (λL=514 nm) on the resonant frequency (f0≊5.4 GHz) of a superconducting parallel‐plate resonator (PPR) consisting of two thin epitaxial YBa2Cu3O7−x films. We demonstrate that laser irradiation shifts the resonant frequency of the PPR with negligible change of quality factor. Photoinduced deviation of f0 strongly depends on the chopping frequency and increases linearly with light intensity. The effect of illumination is attributed to the photoinduced change of the kinetic inductance due to laser heating. This effect may be used to produce phase modulation of the superconducting transmission lines.

Magnetic Properties of La

AC and DC magnetic measurements in temperature interval 5-300 K and at external magnetic field Hles 5 T were employed to probe and compare magnetic ordering in bulk and nanometer-sized (15plusmn2 nm) La0.7Ca0.3MnO3 single crystals. The respective Curie temperatures (TC)~239 K and 233 K, close to each other are observed in bulk and nano samples. While, their low T spontaneous magnetizations are strongly different, being about 3.6 and 1.2 muB/f.u., respectively. AC susceptibility (chi) of a bulk sample, measured at Hdc=0, shows a maximum of chi(T) at T~TC. In a contrast, chi(T) of the nano-sample demonstrates a broad maximum far below its TC. In the nano-sample both real and imaginary parts of chi are frequency dependent within the 5-280 K range. In a contrary, the frequency dependence is observed only for imaginary part of chi in bulk crystal. It is concluded that the similar ferromagnetic ground state exists in both considered samples; however, it is strongly frustrated in agglomerated nano particles due to surface magnetic disorder and interparticle interactions.

_{0.7}

A large nonlinear response of a single crystal of

Ca

{\mathrm{ZrB}}_{12}

_{0.3}

to an ac field (frequency

MnO

40\char21{}2500\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}

_{3}

) for

Manganite Bulk and Nanometer-Sized Crystals

{H}_{0}g{H}_{c2}

Low-frequency response in the surface superconducting state of single-crystal ZrB 12

has been observed. Direct measurements of the ac wave form and the exact numerical solution of the Ginzburg-Landau equations, as well as the phenomenological relaxation equation, permit the study of the surface superconducting state dynamics. It is shown that the low-frequency response is defined by transitions between the metastable superconducting states under the action of an ac field. The relaxation rate that determines such transition dynamics is found.