http://dspace.nbuv.gov.ua:80/handle/123456789/115075 2026-04-24T00:47:52Z http://dspace.nbuv.gov.ua:80/handle/123456789/118645 The magnetic properties of potassium holmium double tungstate Borowiec, M.T.; Dyakonov, V.P.; Khatsko, E.N.; Zayarnyuk, T.; Zubov, E.E.; Szewczyk, A.; Gutowska, M.U.; Rykova, A.I.; Piętosa, J.; Majchrowski, A.; Michalski, E.; Hoffmann, J.-U.; Prokes, K.; Woźniak, K.; Dobrzycki, Ł.; Barański, M.; Domukhovski, V.; Shtyrkhunova, V.; Żmija, J.; Szymczak, H. The magnetic investigations of potassium holmium double tungstate KHo(WO⁴)² have been performed. The results of measurements of magnetic susceptibility and magnetization as a function of temperature (T from 0.3 K up to 100 K) and magnetic field (up to 1.5 T) are presented. A strong anisotropy of magnetic properties was found. The magnetic measurements data were used to calculate the interaction energy. It was shown that the interactions between nearest neighbors Ho³⁺ ions have antiferromagnetic character. 2011-01-01T00:00:00Z http://dspace.nbuv.gov.ua:80/handle/123456789/118644 Soliton states in mesoscopic two-band-superconducting cylinders Kuplevakhsky, S.V.; Omelyanchouk, A.N.; Yerin, Y.S. In the framework of the Ginzburg-Landau approach, we present a self-consistent theory of specific soliton states in mesoscopic (thin-walled) two-band-superconducting cylinders in external parallel magnetic fields. Such states arise in the presence of "Josephson-type" interband coupling, when phase winding numbers are different for each component of the superconducting order parameter. We evaluate the Gibbs free energy of the sysyem up to second-order terms in a certain dimensionless parameter ε ≈ Lm/Lk 1, where Lm and Lk are the magnetic and kinetic inductance, respectively. We derive the complete set of exact soliton solutions. These solutions are thoroughly analyzed from the viewpoint of both local and global (thermodynamic) stability. In particular, we show that rotational-symmetry-breaking caused by the formation of solitons gives rise to a zero-frequency rotational mode. Although soliton states prove to be thermodynamically metastable, the minimal energy gap between the lowest-lying single-soliton states and thermodynamically stable zero-soliton states can be much smaller than the magnetic Gibbs free energy of the latter states, provided that intraband "penetration depths" differ substantially and interband coupling is weak. The results of our investigation may apply to a wide class of mesoscopic doubly-connected structures exhibiting two-band superconductivity. 2011-01-01T00:00:00Z http://dspace.nbuv.gov.ua:80/handle/123456789/118643 Microwave-resonance-induced magnetooscillations and vanishing resistance states in multisubband two-dimensional electron systems Monarkha, Yu.P. The dc magnetoconductivity of the multisubband two-dimensional electron system formed on the liquid helium surface in the presence of resonant microwave irradiation is described, and a new mechanism of the negative linear response conductivity is studied using the self-consistent Born approximation. Two kinds of scatterers (vapor atoms and capillary wave quanta) are considered. Besides a conductivity modulation expected near the points, where the excitation frequency for inter-subband transitions is commensurate with the cyclotron frequency, a sign-changing correction to the linear conductivity is shown to appear for usual quasi-elastic inter-subband scattering, if the collision broadening of Landau levels is much smaller than thermal energy. The decay heating of the electron system near the commensurability points leads to magnetooscillations of electron temperature, which are shown to increase the importance of the sign-changing correction. The line-shape of magnetoconductivity oscillations calculated for wide ranges of temperature and magnetic field is in a good accordance with experimental observations. 2011-01-01T00:00:00Z http://dspace.nbuv.gov.ua:80/handle/123456789/118642 Impurity effects in quasiparticle spectrum of high-Tc superconductors Pogorelov, Yu.G.; Santos, M.C.; Loktev, V.M. The revision is made of Green function methods that describe the dynamics of electronic quasiparticles in disordered superconducting systems with d-wave symmetry of order parameter. Various types of impurity perturbations are analyzed within the simplest T-matrix approximation. The extension of the common selfconsistent T-matrix approximation (SCTMA) to the so-called group expansions in clusters of interacting impurity centers is discussed and hence the validity criteria for SCTMA are established. A special attention is payed to the formation of impurity resonance states and localized states near the characteristic points of energy spectrum, corresponding to nodal points on the Fermi surface. 2011-01-01T00:00:00Z