Electric dipole image forces in three-layer systems: The classical electrostatic model.

General exact analytical expressions have been derived for the image force energy Wi(Z, φ) of a point dipole in a classical three-layer system composed of dispersionless media with arbitrary constant dielectric permittivities εi. Here, i = 1-3 is the layer number, and Z and φ are the dipole coordinate and orientation angle, respectively. It was found that the long-range asymptotics Wi(Z→∞,φ) in both covers (i = 1, 3) are reached unexpectedly far from the interlayer (i = 2). Another specific feature of the solution consists in that the interference of the fields created by polarization charges emerging at both interfaces leads to the appearance of a constant contribution inside the interlayer with a non-standard dependence on the dipole orientation angle φ. It was shown that by changing the dielectric constants of the structure components, one can realize two peculiar regimes of the Wi(Z, φ) behavior in the covers; namely, there arises either a potential barrier preventing adsorption or a well far from the interface, both being of a totally electrostatic origin, i.e., without involving the Pauli exchange repulsion, which is taken into account in the conventional theories of physical adsorption. The results obtained provide a fresh insight into the physics of adsorption in physical electronics, chemical physics, and electrochemistry.

Magnetic moment inversion at giant flux jump: dynamical property of critical state in type-II superconductors.

Experimental evidence of tremendous magnetic moment dynamical inversion, from metastable trapping state to the state with essentially the same moment oriented in the opposite direction, appearing during giant flux jump connected to thermomagnetic avalanche process in superconducting YBa2Cu3O7-δ single crystal, is presented. Magnetization inversion takes place in the system, without thermal contact between sample and sample holder, with a tremendous stored energy once the avalanche process is completed in quasi-adiabatic conditions. A model of magnetic moment inversion, caused by the jump between two metastable states of superconductor with the same energy storage, is presented and discussed in terms of the critical state with peculiar evolution of the critical-current spatial distribution. Importantly, knowledge of conditions of the appearance of such a phenomenon is crucial for applications of bulk superconductors as "permanent" magnets, for example, in superconducting levitation devices, etc.

The phase diagram for coexisting d-wave superconductivity and charge-density waves: cuprates and beyond.

Phase diagrams of d-wave superconductivity characterized by an order parameter Δ coexisting with charge-density waves (CDWs) characterized by an order parameter Σ were constructed for the two-dimensional Fermi surface (FS) appropriate to, e.g., cuprates. CDWs were considered as an origin of the pseudogap appearing at antinodal FS sections of the d(x2-y2) superconductor. Two types of the Σ-reentrance were found: with the temperature, T, and with the opening of the CDW sector, 2α. The angular plots in the momentum space for the resulting gap profile over the FS ('gap roses') were obtained. The gap patterns are rather involved, giving insight into the difficulties of the interpretation of photoemission spectra. It was shown that the Σ-Δ coexistence region exists even for the complete dielectric gapping due to the distinction between the superconducting and CDW order parameter symmetries. The checkerboard and unidirectional CDW configurations were examined, and both the phase diagrams and the behavior with T and α of the order parameters were found to differ. A more general case with a non-zero mismatch angle ß between the superconducting lobes and the CDW sectors was analyzed, the case ß = π/4 corresponding to the d(xy) symmetry of the superconducting order parameter. The phase diagrams were found to be sensitive to ß-variations, showing that internal strains and external pressure can drastically affect the behavior of Σ(T) and Δ(T).

EPR of Mn2+ in the kagomé staircase compound Mg2.97Mn0.03V2O8.

The electron paramagnetic resonance (EPR) of Mn2+ in geometrically frustrated Mg2.97Mn0.03V2O8 single crystals is reported. The complex EPR spectrum shows resonance lines associated with two crystallographically nonequivalent lattice positions of Mn ions that are known in the kagomé staircase system as "cross-tie" and "spine" sites. Additionally, strongly anisotropic resonances of various Mn2+-Mn2+ pairs are observed. The signs and values of the crystal field parameters are determined from EPR spectra. The local magnetic symmetry details of magnetic ions and components of the hyperfine structure tensor are determined for various nonequivalent manganese positions. The exchange coupling between Mn ions in "cross-tie" and "spine" sites is found to be J=41 K.