摘要:

The attenuation of low-frequency acoustic energy in stripes of the low-temperature tetragonal phase of Bi-2212 ceramics is studied taking into account thedx2−y2-symmetry of the superconducting order parameter (SOP) and the dynamic analog of phase separation. The contribution to the energy density of the strain–order parameter coupling leads to a finite value of attenuation in superconductors with a peculiar SOP. The frequency and temperature dependences of attenuation are analyzed and compared with the available experimental results. It is shown that these data are an indirect evidence of the SOP symmetry: thedx2−y2-symmetry for the Bi-2212 phase and thes-symmetry for the Bi–2223 phase. The existence of an ordered low-temperature state responsible for the low-frequency attenuation peak and other anomalies in the properties of Bi-based ceramics in the temperature range 20–40 K is proposed. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593666

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Reentrant spinelsLi0.5Fe2.5−xGaxO4withx=0.9and 1.2 display peaks on the temperature dependences of heat capacityCatT1=13.4&hthinsp;K&hthinsp;(x=0.9)and14.2&hthinsp;K&hthinsp;(x=1.2)respectively, which are typical of a first-order phase transition. This transition is identified with the transformation of the collinear ferrimagnetic structure into a noncollinear structure preceding on the temperature scale the state of ferrimagnetic spin glass existing in the temperature range0&hthinsp;K⩽T⩽Tf,where transition temperaturesTfare9&hthinsp;K&hthinsp;(x=0.9)and12&hthinsp;K&hthinsp;(x=1.2). ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593667

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The existence of additional transverse electric (TE) and magnetic (TM) surface polaritons formed as a result of high-frequency magnetoelectric interaction in a ferroelectric is predicted. The spectrum of the new type of surface polaritons is analyzed for transverse orientation of the electric polarization relative to the crystal surface. These polaritons are different in ferroelectric domains with opposite directions of spontaneous electric polarization. Thus, TE surface polaritons exist only in domains with electric polarization directed into the medium. Besides, magnetoelectric interaction induces effects like birefringence and anomalous dispersion of TM polaritons. Moreover, it is found that TM polaritons can exist in those types of ferroelectrics in which their existence was forbidden earlier. The same effects must also exist not only in ferroelectrics, but also in ordinary dielectrics in a constant electric field at right angles to the crystal surface. The above-mentioned asymmetry of the effects, including their switching on/off, must be observed upon a change in the direction of the applied electric field. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593668

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have analyzed the quantum interference effects in the macroscopic “superconducting molecule.” The composite system consists of two massive superconducting rings, each interrupted by a Josephson junction, which are at the same time weakly coupled with one another. The special case of coupling via the Josephson four-terminal junction is considered. The structure of the macroscopic quantum states in an applied magnetic field is calculated. It is shown that, depending on the values of the magnetic fluxes through each ring, the system displays two groups of states, the “orthostates” with both induced currents going in the same direction, and the “parastates” with the opposite currents and with the total induced flux locked to zero value. The transition to the flux locked state with changing of the total applied flux is sudden and is preserved in a certain interval which is determined by the difference of the fluxes applied through each ring. It makes the system sensitive to small gradients of the external magnetic field. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593669

出版商:AIP    

年代:1998

数据来源: AIP