International Journal of Modern Physics B

We briefly describe the recent development of the optical evanescent-field amplifiers including the solid-state integrated-optic and fiber-optic devices. Application of these amplifiers to the optical communication systems is discussed.

Very high-resolution electrical resistivity data have been presented for Zr-rich (Cu_0.36Zr_0.64)_1-xAl_x and (Ni_0.5Zr_0.5)_1-xAl_x(0≤x≤0.2) non-magnetic transition-metal-based amorphous metallic glasses in the temperature range of 1.2–300 K. All the alloys are found to fall into the strong–scattering regime (ρ₃₀₀>165μΩ·cm) with negative temperature coefficient of resistance even till 300 K. With the addition of Al in both the systems, the value ρ₃₀₀ increases because of the enhancement of the degree of disorder. In the low-temperature range, they show a tendency towards superconductivity with trasition temperature T_c<4.2 K and large superconducting fluctuations. They are found to be extreme type-II dirty BCS superconductors. A quantitative analysis of the electrical resistivity, based on the electron–electron interaction and localization effects, is reported here in the temperature range, T_c<T<300 K. We find, in each specimen, three distinct regions, hitherto only theoretically predicted where the conductivity varies in a sequence of , T and at low, intermediate and high temperatures, respectively. The only earlier similar observation was made in a ferromagnetic system where the interpretation in terms of quantum interference effects will always remain controversial. A number of parameters, namely, the coefficient of the term at low temperatures, diffusion constant, density of states at the Fermi level, inelastic mean free path and relaxation time, estimated from this quantum correction analysis, are in excellent agreement with those from earlier experiments on other amorphous systems.

Low field magnetic measurements of a re-entrant system Ni₈₁Mn₉₁ as a function of temperature are shown to exhibit two successive transitions. The ac susceptibility shows strong frequency dependence due to the frustrated spins. The freezing temperature, T_f, shifts to higher temperatures with increasing frequency and decreasing ac field amplitude. Its dependence on frequency is associated with the viscuous relaxation of spins during an ac cycle of the measuring field, which can be attributed to the magnetic relaxation of spin clusters. The results support the theory that re-entrant spin glass state is coexistent with the ferromagnetic domains and that no real phase transition to a spin glass state seems to occur. The interplay of magnetic domain formation and movement with the so-called frustrated spins appears to be responsible for the observed dependences.

In this work, the influence of the amorphization effect of C⁺, O⁺ and Cr⁺, implantation on the friction and wettability properties of pure titanium (grade 2) has been studied. Doses from 1×10¹⁷ to 5×10¹⁷ ions cm^-2 at multiple energies of 50 to 190 keV have been used. Additionally, pin-on-disk tribological tests using Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) pins under lubricated conditions and wettability measurements of implanted and unimplanted titanium samples were carried out. We found, that the more suitable material for the wettability and hence wear resistance is C⁺ implanted titanium, because of its higher surface energy than the unimplanted titanium corresponding energy. Friction tests on monoenergetic 180 keV C⁺ and O⁺ modified titanium with 1×10¹⁷ ions cm^-2 have showed an essentially reduced friction compared to samples implanted with the same dose but at multiple energies. A reduction of the wettability by about 7% and the friction coefficient by about 18% was observed for carbon implanted titanium with a dose of 1×10¹⁷C⁺ cm^-2; this effect corresponds to a good correlation between wettability and friction coefficient after C⁺ implantation in titanium. It was concluded that the reduction of the friction coefficient with monoenergetic C⁺ implanted titanium is 3.7 times lower compared with those of pure titanium. This important result could extend the average lifetime of orthopaedic components of approximately 2 orders of magnitude.

An explanation of the remarkable singular behavior of the shear viscosity of ultrathin liquid films is presented. The "universal" viscosity law η_eff ~ (|v|/d)^-a originally observed by Hu, Carson and Granick [Phys. Rev. Letts.66, 2758 (1991)] is derived and the exponent a is found to be a = 1-δ^-1 where δ is the critical exponent for a corresponding second order phase transition in the film. This exponent can take either the classical (mean field) value δ = 3, or other, nonclassical values depending on the universality class of the surface phase transition.

Hamiltonians of electron–phonon interaction for thin metallic films are formulated. This is the basis for the estimate of the superconductivity critical temperature for films and corresponding bulk structures. It is shown that the interaction of surface electrons in the film with bulk phonons could explain the experimental fact that critical temperatures of the films are higher than the corresponding ones in bulk (massive) structures. Since above fact is valid nearly for all pure metallic, one can conclude that the dominant form or the interaction in films is the interaction of surface electrons with bulk phonons.

By the moment method established previously on the basis of the statistical mechanics, the thermodynamic properties of a strongly anharmonic face-centered and body-centered cubic crystal with point defect are considered. The thermal expansion coefficient, the specific heat C_v and C_p, the isothermal and adiabatic compressibility, etc. are calculated. Our calculated results of the thermal expansion coefficient, the specific heat C_v and C_p… of W, Nb, Au and Ag metals at various temperatures agrees well with the measured values. The anharmonic effects in extended X-ray absorption fine structure (EXAFS) in the single-shell model are considered. We have obtained a new formula for anharmonic contribution to the mean square relative displacement. The anharmonicity is proportional to the temperature and enters the phase change of EXAFS. Our calculated results of Debye–Waller factor and phase change in EXAFS of Cu at various temperatures agrees well with the measured values.

A phenomenological Landau-like theory is presented here, which describes the nematic and smectic-A phase. The problem of the first or second order nature of the nematic to smectic-A phase transition is explored and the stability of the different phases are also calculated. On the basis of this work it is argued that the nematic to smectic-A transition is of first order nature.

This work presents our investigations of mezomorphic properties of two polymorphic liquid crystals, namely, 4-nonyloxy-4-butoxyphenyl benzoate and N-(-4-heptyloxybenzylidene-4-butylaniline) in a wide temperature range, particularly, in the phase transition regions. By means of an original experimental method, the heterophase regions and also the phase transition temperatures have been determined for these materials with high accuracy. These phase transition intervals have been analyzed using a mean field model.