Yu. A. Kumzerov

Ferroelectrics properties of nanosize KDP particles

The low frequency dielectric permittivity measurements were performed on the KDP nanosize particles system. The highly dispersed objects were obtained by introducing of ferroelectric material into the pores of different dielectric matrixes. The significant shift of transition temperature from the bulk value as well as the transition broadening for the KDP particles samples was observed.

Luttinger-liquid-like transport in long InSb nanowires

Long nanowires of degenerate semiconductor InSb in asbestos matrix (wire diameter about 50 A, length 0.1-1 mm) have been prepared. The electrical conduction of these nanowires has been studied over a temperature range 1.5-350 K. The zero-field electrical conductance is a power function of temperature G∝Tα with a typical exponent α≈4. Current-voltage characteristics of such nanowires are nonlinear and, at sufficiently low temperatures, follow the power law I∝Vβ. The electrical conduction of the nanowires cannot be accounted for in terms of ordinary single-electron theories and exhibits features expected for impure Luttinger liquid (LL). For the simple approximation of an impure LL as a pure liquid broken into drops by weak links, the estimated weak-link density is around 103-104 cm-1.

Josephson properties of the three-dimensional regular lattice of the weakly coupled nanoparticles

Abstract Regular three-dimensional lattices of superconducting weakly coupled nanoparticles have been prepared on a base of crystalline porous dielectric matrices. The results of DC and AC measurements show that prepared materials behave like continuum Josephson media which exhibit mutual phase-locking.

Nuclear magnetic resonance, resistance and acoustic studies of the melting-freezing phase transition of gallium in Vycor glass

The melting-freezing phase transition of gallium confined within Vycor glass was studied by NMR, resistance and acoustic techniques. A single although broadened 71Ga NMR line corresponding to melted gallium was observed in contrast to lineshapes found until now for liquid gallium in porous matrices. A difference between results obtained using the three methods was explained by formation of various confined solid gallium modifications. A depression of the freezing and melting phase transition temperatures and a pronounced hysteresis in the melting-freezing processes were found and are discussed. Heterogeneous nucleation was suggested to explain the dependence of crystallization on temperatures of pre-warming. Irreversible melting was observed for the second gallium modification.

X-ray and resistance studies of the melting and freezing phase transitions for gallium in an opal

The melting and freezing processes and the structure of gallium in an opal were studied using x-ray powder diffraction within the temperature range 10 to 320 K. Four different modifications of solid confined gallium were found. Two of these modifications did not coincide with any known gallium structures; another two coincided with and disordered . The broadening of the total melting and freezing processes and reduction of the phase transition temperatures compared to bulk phase were obtained. The size of confined gallium crystallites corresponding to the different modifications was estimated for cooling and warming. The reproducible freezing was treated as a result of the steep temperature dependence of the nucleation rate in supercooled melts. Additional measurements of resistance for the opal filled with gallium revealed that it was sensitive mainly to the melting and freezing within the gallium modification coinciding with disordered . Melting-freezing hysteresis for this modification was found to depend on temperatures of pre-warming. It was suggested that the freezing of this modification is driven by the amount of frozen crystallites of the phase with the highest onset of freezing. The melting broadening and the lowering of the phase transition temperatures for the confined gallium modifications were discussed.

Unconventional magnetoresistance in long InSb nanowires

Magnetoresistance in long correlated nanowires of degenerate semiconductor InSb in asbestos matrix (wire diameter of around 5 nm, length 0.1–1 mm) is studied in the temperature range 2.3–300 K. At zero magnetic field, the electric conduction G and the current-voltage characteristics of such wires obey the power laws G∞ Tα, I∞ Vβ, expected for one-dimensional electron systems. The effect of the magnetic field corresponds to a 20% growth of the exponents α, β at H = 10 T. The observed magnetoresistance is caused by the magnetic-field-induced breaking of the spin-charge separation and represents a novel mechanism of magnetoresistance.

X-ray studies of the melting and freezing phase transitions for gallium in a porous glass

We use x-ray powder diffraction to study the melting and freezing processes for gallium within a porous glass. The only modification to solid gallium was found above 20 K, in contrast with previous x-ray studies of confined gallium. The size of gallium crystallites remained nearly constant during cooling and warming, while both the melting and freezing processes were smeared. The size of confined gallium crystallites was estimated as 22 nm, which is significantly larger than the pore size. The reasons for the phase-transition broadening and hysteresis between freezing and melting are discussed on the basis of the results obtained. @S0163-1829~98!02942-7#

Nuclear magnetic resonance and acoustic investigations of the melting - freezing phase transition of gallium in a porous glass

The melting - freezing phase transition of gallium in a porous glass was studied by NMR and acoustical techniques. A depression of the freezing and melting phase transition temperatures and a pronounced hysteresis in the melting - freezing processes were found. An intricate NMR lineshape for liquid gallium was observed with a temperature coefficient of the Knight shift more than twice that measured for the bulk melt. The results are discussed on the basis of the Gibbs - Thompson equation and by means of a geometric freezing model.

THE ORIENTATIONAL-ORDERING TRANSITION IN SINGLE CRYSTALS OF SELECTED C60 COMPLEXES WITH ORGANIC DONORS FOLLOWED BY INFRARED SPECTROSCOPY

Abstract Investigations of infrared spectra of single crystals of the complex of fullerene C60 with dianthracene (DAN) and C60 grown from CS2 solution (clathrate) versus temperature, between 4 and ca. 430 K, have been performed. A phase transition for the complex and the clathrate accompanied by a splitting of the F1u(4) band into at least two components was detected at temperatures higher than 260 K. The line splitting was attributed to C60 symmetry lowering as a result of suppression of its rotation. Phase transitions at 80, 160 and 305 K have been observed for DAN C60 (C6H6)3; the nature of the transitions has been suggested.

Superconductivity of gallium in porous glass

Abstract Superconductivity of gallium embedded in the porous glass with average pore size of 4 nm was studied using a SQUID magnetometer. Hysteretic behavior at both high and low magnetic fields was observed. The quantitative model of the superconducting properties of the porous glass with gallium has been developed on the bases of the measurements performed. The phase diagram in the H − T plane, including the irreversibility line, was obtained.