# acta physica slovaca

Acta Physica Slovaca 52(2002)
• V. Yu. Lazur, V. M. Dobosh, V. V. Rubish, S. Chalupka, M. Salák
Hidden symmetry and separation of variables in the two-centre problem with a confinement-type potential
Acta Physica Slovaca 52, 41 (2002)

Abstract: An additional spheroidal integral of motion and a group of dynamic symmetry in a model quantum-mechanical problem of two centres eZ1Z2  with Coulomb and oscillator interactions is obtained, the group properties of its solutions being studied. P(3) \otimes P(2,1), P(5,1) and P(4,2) groups are considered as the dynamic symmetry groups of the problem, among them P(3) \otimes P(2,1) group possessing the smallest number of parameters. The obtained results may appear useful at the calcuations of QQq-baryons and QQg-mesons energy spectra.

• Š. Lányi
Assessment of sensitivity and resolution limits of scanning capacitance microscopes
Acta Physica Slovaca 52, 55 (2002)

Abstract: Based on analysis of noise limited sensitivity of different capacitance detection methods, the achievable lateral resolution of Scanning Capacitance Microscopes has been estimated. The ultimate sensitivity is below 3 x 10-21 F/sqrt(Hz)/V. A lateral resolution of about 2 nm is expected with probes with 7-nm radius of curvature. About 5 nm has been already achieved with a tip radius of approximately 25 nm. Improving the signal-to-noise ratio using larger applied voltage than a few volts must lead to degradation of lateral resolution, since the tip-to-sample distance has to be increased to prevent voltage breakdown or excessive tunnelling to occur.

• L. L. Chotorlishvili, I. M. Nadareishvili, P. A. Kurashvili
Two-pulse spin echo in two-level systems inside amorphous ferromagnets
Acta Physica Slovaca 52, 65 (2002)

Abstract: The dependence of Mims echo on time, caused by the existence of two-level systems within 180$^\circ$ Bloch domain walls has been considered. It is shown that in the case of two-level systems, the two-pulse echo formation is characterized by some specific features due to the wide distribution of the two-level systems splitting energy.

• D. Kulak
The soliton ground state of an electron or exciton in the extended Jahn-Teller system in one dimension
Acta Physica Slovaca 71, 639 (2002)

Abstract: In this paper a variational method for the intermediate ground state of a quasiparticle (exciton, electron or hole) interacting with dispersionless optical vibrations in a one-dimensional chain of the E-e Jahn-Teller systems is investigated. The intermediate and strong nonadiabatic range constitutes a kind of "critical" region, where the electron-phonon coupling constant g and the nonadiabatic parameter  are approximately equal to one. We have investigated the conditions for the existence and for the stability of a soliton ground state of the extended one-dimensional Jahn-Teller system in one dimension which is affected by quantum fluctuations of optical phonons. The soliton was found to be stable for a sufficiently strong electron-phonon coupling strength. Although the nonadiabatic parameter  is chosen sufficiently large, comparable to one, the presented model for the one-dimensional chain of the E- Jahn-Teller systems leads to substantially lower ground state energies, in contrast with one which is presented in previous studies. Our soliton ground state energies, for the one-dimensional chain of the E- Jahn-Teller systems, are in good agreement with those which are presented for the one-dimensional chain of one-level molecules in previous studies.

• V. Hronský, J. Murín
Thermally stimulated depolarization and mechanical relaxation study of glass transition in polyvinylidene fluoride
Acta Physica Slovaca 52, 91 (2002)

Abstract: Measurements of the thermally stimulated depolarization currents (TSDC) have been employed to investigate molecular motion at glass transition in polyvinylidene fluoride (PVDF). Biaxially drawn film material was submitted to various conditions of sample polarization and isolated TSDC peaks were itted by different equations for temperature dependence of relaxation time. For relaxation process at Tg were obtained: glass transition temperature Tg, apparent activation energy Ea and pre-exponential factor 0 (Arrhenius), average thermal expansion coefficient of free volume f, pre-exponential factor _\infty, temperature T_\infty (Vogel), dipolar strength  = s - _\infty, the relaxation frequency of the dominant realignment process at Tg. The results obtained by means of TSDC method are compared with the ones obtained by dynamic-mechanical measurements.