摘要:

NMR investigations of restoration of longitudinal equilibrium magnetization in phase-separated solid3He–4Hemixtures are carried out in the temperature range 1–200 mK. It is found that below 100 mK, the results depend on the energy of tipping NMR pulses, while at the lowest temperatures the restoration of magnetization becomes nonmonotonic. The obtained results are explained on the basis of a proposed model in which both magnetic (spin-lattice) and thermal relaxation are assumed to take place between the Zeeman system and the lattice. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593522

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Equilibrium states are calculated for a planar hexagonal antiferromagnet in a magnetic field oriented in the basal plane. As the field is rotated in the basal plane, a number of first-order phase transitions accompanied by magnetization jumps are observed in the range of metastable states in the system. The range and equilibrium parameters of the thermodynamically stable domain structure formed in the vicinity of such transitions are determined. Magnetization curves inRbMnCl3are analyzed. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593515

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Screening of the electric field of a test charge by monolayer and double-layer composite fermion systems is considered taking into account the influence of the sample boundary. It is shown that the test charge field is partly screened in the system at distances much larger than the magnetic length. The value of screening as a function of distance depends considerably on the filling factor. The effect of variation of the value of screening in a double-layer system upon a transition to a state described by the Halperin wave function is determined. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593516

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The point-contact spectroscopy is used to study singularities of the electron–phonon spectra of heterojunctions made of different metals Cu–Cu (1 at. &percent; Fe) and Cu–Au. Measurements at high frequencies made it possible to distinguish and identify contributions to the spectrum from the nonequilibrium phonon relaxation. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593517

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A non-traditional point of view to the nature of anomalous skin effect is proposed on the basis of an analysis of the problem of coupling modes in the electron plasma of a metal. It is shown that the anomalous skin effect in an applied magnetic field is in fact the result of interaction and coupling of a number of intrinsic electromagnetic modes excited due to nonlocal effects and specific properties of doppleron modes. It is proved that the magnetic field dependence of anomalous skin effect is determined by the shape of the Fermi surface of the metal and that the classical anomalous skin effect in the model of free electrons is just a special case. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593518

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The influence of heating of two-level systems on low-temperature spin–lattice relaxation is studied. Effects of the type of a “phonon bottleneck” are investigated in amorphous substances in which the role of resonant phonons is played by resonant tunnel two-level systems. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593519

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The form of the exciton absorption band for1Dmolecular chains and their luminescence are investigated in glass matrices of various composition and in Langmuir–Blodgett (LB) films under selective excitation. It is shown that the exciton absorption band for1Dchains is always asymmetric. The shape of the low-frequency edge of their absorption band changes from the Gaussian to the Lorentzian depending on the method of obtaining of1Dchains due to a change in the diagonal and off-diagonal disorder in molecular chains. Under selective excitation of1Dmolecular chains, the effect of considerable luminescence band narrowing is not observed. This is associated with statistical properties of the exciton absorption band and with relaxation processes in the materials under investigation in the excited state. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593520

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We consider the energy stored in a one-dimensional ballistic ring with a barrier subjected to a linearly time-dependent magnetic flux. An exact analytical solution for the quantum dynamics of electrons in the ring is found for the case when the electromotive force multiplied by the electron charge,e&Vegr;,is much smaller than the interlevel spacing, &Dgr;. Electron states exponentially localized in energy space are found for irrational values of the dimensionless ratioA≡&Dgr;/2e&Vegr;.Relaxation limits the dynamic evolution and the localization does not develop ifAis sufficiently close to a rational number. As a result the accumulated energy becomes a regular function ofAcontaining a set of sharp peaks at rational values with small enough denominators (fractional pumping). The shape of the peaks and the distances between them are governed by the interplay between the strength of backscattering and the relaxation rate. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593523

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have carried out low-temperature x-ray diffraction studies onC60fullerite polymerized by low quasi-hydrostatic pressure of 1.1 GPa atT=563 K.It is established that at room temperature in freshly prepared samples three phases mainly coexist, viz. a compressed cubic phase with the lattice parametera=13.94 Å,an orthorhombicO′phase with the lattice parametersa=9.12 Å,b=9.82 Å,c=14.60 Å,and a rhombohedral phase of symmetryR3mwith the parametersa=9.20 Åandc=24.27 Å.Mechanical grinding or annealing at 573 K entails depolymerization of sintered samples and restoration of the fcc structure of pristineC60.During annealing in air, intercalation of fullerite lattice by oxygen molecules occurs as well as a substantial amount of some new phase is formed, most probably with tetragonal symmetry, the chemical composition and structure of which have not been determined. The microhardness of polymerizedC60is higher than that of single crystal samples roughly four-fold at room temperature and by a factor of 2.6 at liquid nitrogen temperature. Analysis shows that polymerization and grain boundaries give contributions to the microhardness of sintered samples but we did not succeed in separating these two contributions. The temperature dependence of the microhardness of polymerized samples exhibits a jump in the vicinity of 260 K, where pristineC60fullerite undergoes the fcc-sc phase transition. We think that this jump is due to a partial destruction of the polymerized state under indentor as a result of shear straining in inhomogeneous stress fields. Annealing of polymerizedC60at a temperature of 573 K, which restores the fcc phase, leads to a considerable decrease in microhardness, the hardness “jump” near the fcc-sc transition extends in temperature and shifts to lower temperatures. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593524

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Acoustic relaxation in undeformed and plastically deformed CsI single crystals is studied using the composite oscillator technique at frequencies(1–7)×105&hthinsp;Hzin the temperature range 2–15 K. Plastic deformation leads to the emergence of an internal friction peak localized in the temperature range 4–5 K. It is shown that the peak is shifted towards higher temperatures upon an increase of the vibrational frequency and corresponds to a thermally activated relaxation process with very low values of activation energyU≈1.9×10−3&hthinsp;eVand the attack frequency&ngr;0≈6.7×108&hthinsp;s−1.The interaction of sound with dislocation kinks migrating in the second-order Peierls relief is considered as a possible mechanism of peak formation. ©1998 American Institute of Physics.

ISSN:1063-777X    

DOI:10.1063/1.593521

出版商:AIP    

年代:1998

数据来源: AIP