Superconductivity of polar many-valley semiconductors and semimetals

A polar, degenerate semiconductor with two equivalent isotropic valleys, and a semimetal with equal effective masses for the holes and electrons were studied within the framework of a modified Gurevich-Larkin-Firsov model by taking into account the intervalley pairing. Concentration dependencies are found for the critical temperature which agree qualitatively with experimental data for SrTiO3 and BaPb(1-x)Bi(x)O3

Formation of Root Singularities on the Free Surface of a Conducting Fluid in an Electric Field

The formation of singularities on a free surface of a conducting ideal fluid in a strong electric field is considered. It is found that the nonlinear equations of two-dimensional fluid motion can be solved in the small-angle approximation. This enables us to show that for almost arbitrary initial conditions the surface curvature becomes infinite in a finite time.Comment: latex, 6 pages, no figure

Equivalence among optimization problems on matrix sets

AbstractTreatment of optimization problems on matrix sets is a general framework for the study of some large classes of discrete programming problems, for the investigation of connections between different classes of such problems. An appropriate formalism is introduced. It gives a possibility to include in this study bottle-neck problems and other combinatorial optimization problems over totally ordered commutative semigroups. Concepts of equivalency and of weak equivalency are defined and some general equivalency theorems are proved. The main problem under discussion is for which problems an equivalent problem over a finite ordered algebraic structure can be constructed

Raising Tc in charge density wave superconductor ZrTe3 by Ni intercalation

We report discovery of bulk superconductivity in Ni0.05ZrTe3 at Tc = 3.1 K, obtained through Ni intercalation. Superconductivity coexists with charge density wave (CDW) state with TCDW = 41 K. When compared to parent material ZrTe3, filamentary superconducting transition is substantially increased whereas TCDW was suppressed. The analysis of superconducting state indicates that Ni0.05ZrTe3 is an intermediately coupled superconductor.Comment: 5 pages, 5 figure

Magnetic field and pressure effects on charge density wave, superconducting, and magnetic states in Lu5_5Ir4_4Si10_{10} and Er5_5Ir4_4Si10_{10}

We have studied the charge-density-wave (CDW) state for the superconducting Lu$_5$Ir$_4$Si$_{10}$ and the antiferromagnetic Er$_5$Ir$_4$Si$_{10}$ as variables of temperature, magnetic field, and hydrostatic pressure. For Lu$_5$Ir$_4$Si$_{10}$, the application of pressure strongly suppresses the CDW phase but weakly enhances the superconducting phase. For Er$_5$Ir$_4$Si$_{10}$, the incommensurate CDW state is pressure independent and the commensurate CDW state strongly depends on the pressure, whereas the antiferromagnetic ordering is slightly depressed by applying pressure. In addition, Er$_5$Ir$_4$Si$_{10}$ shows negative magnetoresistance at low temperatures, compared with the positive magnetoresistance of Lu$_5$Ir$_4$Si$_{10}$.Comment: 12 pages, including 6 figure

Image Forces in Physics and Chemistry of Surfaces: Certain Fundamental Aspects

The occurrence and role of image forces in physics and chemistry of surfaces are analyzed. It is shown that a prima facie simple concept of classical electrostatics has a very complicated background of diverse many-body phenomena. In particular, attention is focused on dynamic effects usually small but, nevertheless, important due to their peculiar manifestations.Аналізуються використання та роль дзеркальних у фізиці та хімії поверхні. Показано, що, на перший погляд, проста концепція класичної електростатики має непросте підґрунтя, пов’язане із розмаїтими багаточастинковими ефектами. Зокрема, звернено увагу на динамічні аспекти, зазвичай малі, проте важливі через свої особливі прояви.Анализируются использование и роль сил изображения в физике и химии поверхности. Показано, что, на первый взгляд, простая концепция классической электростатики имеет сложную подоплёку, связанную с разнообразными многочастичными эффектами. В частности, привлекается внимание к динамическим аспектам, обычно малым, но, тем не менее, важным из-за своих особенных проявлений