摘要:

The spectrum and damping factor of plasma and magnetoplasma waves in a two-dimensional electron gas at low temperatures are calculated, taking into account local electron states at impurity atoms. It is shown that localization of electrons decreases the frequency of long-wave plasmons and rearranges the magnetoplasma spectrum in the vicinity of resonant frequencies of electron transitions between the Landau levels and local levels. As a result, the plasma absorption peak is displaced towards low frequencies, and the magnetoplasma peak splits. The characteristics of plasmons and magnetoplasmons are calculated for parameters of the inversion layer at the boundary between silicon and silicon dioxide. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593491

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Kramers theory (1940) describing a thermally activated escape of a particle from a potential well in a viscous medium is used for explaining the acoustic absorption peak discovered by Kramer and Bauer (1967) in niobium in the liquid helium temperature range. It is shown that the properties of the peak observed in experiments correspond to the model of resonant interaction of acoustic vibrations with dislocation kink chains. Kinks, viz., pseudoparticle excitations on dislocation lines, perform diffusive drift in the second-order Peierls relief under the action of acoustic vibrations, experiencing simultaneously viscous drag exerted by conduction electrons. The possibility of a sharp controllable change in electron viscosity during a superconducting transition can be used for verifying the conclusions of the Kramers theory in experimental investigations of the dislocation contribution to attenuation of sound. It is found that at low temperatures, the conditions for the observation of the anomaly predicted by Kramers are created for kinks in niobium: the diffusion mobility of particles increases with the dynamic drag coefficient. This circumstance makes it possible to explain one of the most interesting properties of the Kramer–Bauer peak which could not be interpreted correctly till now, i.e., the displacement of the peak towards low temperatures during a magnetic field induced transition ofNbfrom the superconducting to the normal state. The possibilities of observation of quantum diffusion of kinks in acoustic experiments are also considered briefly. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593492

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Poisson brackets are obtained for dynamic variables of a quadrupole magnet, i.e., the spin density and the matrix of the quadruple moments. The starting point for the analysis is the derivation of the kinematic component of the Lagrangean of the system. Equations of motion are derived, and the number of Goldstone and activation modes is determined for the case when the energy functional is invariant to spin rotations. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593493

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The paramagnetic susceptibility of a2Dmetal with an arbitrary charge carrier density is calculated. It is shown that the temperature dependence of the susceptibility displays a clearly manifested nonmonotonisity upon a transition from the normal to an “abnormal” (also nonsuperconducting) phase whose one-particle spectrum contains a pseudogap. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593494

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Experimental data on temperature dependences of the dislocation component of the modulus defect are obtained for some bcc metals (Mo, Fe, and Nb) of different purity and orientation. Measurements are made at frequencies&ohgr;/2&pgr;≃90 kHzin the temperature range 6–300 K. It is found that the modulus defect in Mo and Fe single crystals increases monotonically with temperature starting from 6 K. The increase in the modulus defect becomes stronger in temperature intervals in which relaxation peaks were observed earlier on the temperature dependences of absorption. It is shown that such a behavior of the modulus defect is due to some thermally activated dislocation processes with a broad distribution of activation parameters, which occur in the given temperature range. In contrast to Mo and Fe, Nb shows no temperature dependence of the modulus defect up to 170–200 K, but at higher temperatures it increases rapidly. The existence of a broad temperature region in which the modulus defect is constant indicates that thermally activated processes with a relaxation time close to the reciprocal cyclic frequency1/&ohgr;are either absent or suppressed considerably in this temperature range. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593495

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The thermal expansion of fulleriteC60has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below∼3.4 Kthe linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed. ©1997 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593498

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:1063-777X    

DOI:10.1063/1.593482

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:1063-777X    

DOI:10.1063/1.593481

出版商:AIP    

年代:1997

数据来源: AIP