摘要:

The reflection spectra of YBaCuO superconducting films with moderate and optimal doping are measured in the IR region(2500–10000 cm−1)by varying temperature in the interval 5–200 K. The experimental results convincingly confirm an optical response to the superconducting transition occurring at the pointT=Tcand the sensitivity of optical IR spectra to the phase ordering temperatureT=T*>Tc.It is found that samples with optimal doping display reproducible temperature changes atT*>Tc.It is shown that the two-component model of carriers, including light fermions and heavy bosons, is most adequate for a description of the entire body of optical data. Optical data are used for reconstructing the phase diagram forYBa2Cu3O6+xin theTvs.xcoordinates. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593563

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The two-orbital Hubbard model is used to obtain formulas for the fermion excitation spectrum in the energy bands hybridized by Anderson’s interaction. A transition to the Hubbard operators, which diagonalizes the one-site part of the Hamiltonian, allows us to use the Green’s temperature function technique to take into account the interstitial jump term while studying the superconducting properties of the model. An analysis of the lower part of the energy spectrum leads to a formula for the superconducting transition temperatureTcassociated with the pairing of quasiparticles in one of the correlated bands. The dependence ofTcon electron concentration and energy parameters determining the intraatomic correlation is studied. Proposing a simple relation between the value of pressure(P)and width of the correlated band, the dependence ofTcon the pressure was defined. Good agreement between the theoretical calculation of the dependence ofTcon the pressure and the experimental results forY1−xPrxBa2Cu3O7−&dgr;is found. Comparison of the theoretical and experimental results for the dependence ofTcand its derivatived(ln Tc)/dPon Sr and Bi-content(x)inLa2−xSrxCuO4has been made. It is concluded that the model under consideration can be used for the description of the shift inTcunder pressure for a number of superconductors. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593564

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The longitudinal,&rgr;xx(T),transverse,&rgr;xy(T),and Hall,&rgr;H(T)resistivities have been measured forYBa2Cu3Ox(YBCO) films, showing positive resistivity buckling and those with usual linear&rgr;xx(T)dependence. In the former case unexpected peak on&rgr;xy(T)and unusual&rgr;H(T)dependence with double sign change just above transition temperatureTchave been revealed. The data are analyzed using recent theory for the sign of the Hall conductivity in strongly correlated systems. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593565

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The two-sublattice model of an easy-axis antiferromagnet is used to show that an additional rhombic anisotropy induced by an external magnetic field can lead to the formation of a generalized nuclear spin wave near the surface of the magnet. The criterion for the existence of a generalized surface spin wave is formulated. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593566

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The relaxation parameters of charge carriers in aluminum are measured by investigating the attenuation of electron sound and acoustic wave transfer under Doppler-shifted cyclotron resonance. It is shown that the electron–electron relaxation rate at spherical parts of the hole sheet of the Fermi surface is close to the results of the theory (A. Jaquier &etal;, Phys. Rev.B52, 13005 (1995)) that takes into account the electron–electron interaction with the exchange of virtual phonons. At the same time, the experimental anisotropy of the electron–electron scattering is considerably smaller than the calculated value. A noticeable anisotropy of the electron–impurity collisions frequency in aluminum is discovered. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593567

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The temperature dependence of the kinetic electronic characteristics (conductivity, magnetoresistance, Hall e.m.f.) is studied in the temperature interval 3–50 K on epitaxial silicon crystals having a &dgr; ⟨Sb⟩ layer with sheet concentrations of Sb atoms1×1013and5×1012 cm−2.The shape of the current–voltage characteristics is determined at various temperatures. It is found that the low-temperature kinetic phenomena in these objects are governed by the hopping mechanism of conductivity. A variable range hopping conductivity is observed at sufficiently low temperatures(<10 K).The nonlinearity of the current–voltage characteristics is explained by the theory of non-Ohmic hopping conductivity in moderately strong electric fields. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593568

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The amplitude-frequency dependence of the doppleron–phonon resonance (DPR) in tungsten is investigated experimentally and theoretically. The analysis is based on the general theoretical consideration of propagation and interaction of ultrasonic and electromagnetic modes in metals. It has been established that the weak doppleron–phonon interaction takes place in tungsten in the frequency range used (10–500 MHz). The complicated experimental amplitude–frequency dependence of DPR can be explained under the assumption of predominance of the induction mechanism of interaction between the electronic and ionic subsystems of the metal. It is found that under such an assumption, this dependence is of a general character and is not determined by the shape of the Fermi surface of the metal. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593569

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The effect of a boson peak (BP) on the low-temperature electron spin–lattice relaxation in amorphous materials is investigated. It is shown that the contribution of the boson peak to one-phonon relaxation for EPR frequencies within the boson peak width dominates over the Debye contribution, and the field dependence of relaxation rate changes qualitatively, while the temperature dependence remains unchanged. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593570

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The effect of low temperature (77 K) deformation by drawing (80&percent;) on the superconducting properties and structure of vanadium is studied. The structural elements (fragment boundaries) responsible for the observed changes of critical parameters are isolated. The electron-phonon coupling constant and the electron mean free path undergo most significant changes in these regions of rotational deformation localization, which have a high density of defects and are powerful sources of internal stresses. The dislocation density at the fragment boundaries is estimated. ©1998 American Institute of Physics. This paper is written in commemoration of the 70th anniversary of the National Science Center “Kharkov Physicotechnical Institute”

ISSN:1063-777X    

DOI:10.1063/1.593571

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The paper reports on the results of high-resolution field emission microscopy technique and its application for a qualitative analysis of the local chemical composition of superconducting Nb–Ti alloys. Previous investigations based on field ion microscopy revealed that a superconducting wire made of Nb–60 at. &percent;Ti alloy contains thin and extended regions with a composition close to Nb, which form current-carrying paths with a density4×1010 cm−2.The formation of such zones is associated with rising diffusion occurring during thermal treatment and correlates with high critical currents. The development of the high-resolution field emission microscopy has made it possible to refine considerably in the present work the distribution of precipitated components and the configuration of the current-carrying system. The obtained results confirm that high current-carrying properties of Nb–Ti alloys are due to the presence of phases with a composition close to pure Nb precipitated as a result of thermomechanical treatment and forming a three-dimensional lattice of inclusions. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593572

出版商:AIP    

年代:1998

数据来源: AIP