Table of contents

High T_c superconductors in small magnetic fields directed away from the crystal symmetry axes have been found to exhibit inhomogeneous chains of flux lines (vortices), in contrast to the usual regular triangular flux line lattice. We review the experimental observations of these chains, and summarize the theoretical background that explains their appearance. We treat separately two classes of chains: those that appear in superconductors with moderate anisotropy due to an attractive part of the interaction between tilted flux lines, and those with high anisotropy where the tilted magnetic flux is created by two independent and perpendicular crossing lattices. In the second case it is the indirect attraction between a flux line along the layers (Josephson vortex) and a flux line perpendicular to the layers (pancake vortex stack) that leads to the formation of chains of the pancake vortex stacks. This complex system contains a rich variety of phenomena, with several different equilibrium phases, and an extraordinary dynamic interplay between the two sets of crossing vortices. We compare the theoretical predictions of these phenomena with the experimental observations made to date. We also contrast the different techniques used to make these observations. While it is clear that this system forms a wonderful playground for probing the formation of structures with competing interactions, we conclude that there are important practical implications of the vortex chains that appear in highly anisotropic superconductors.

The adsorption of alkali metals on graphite has been the subject of various studies for the past two decades. Briefly, two main reasons can be offered to justify the persisting interest in these adsorption systems. First, experiments have pointed out intriguing structural phase transitions of the adsorbed species, and, second, in an attempt to explain the experimental results, the more complicated question of the nature of alkali metal–graphite bonding arose. Despite the relative simplicity of the electronic structure of the alkali metals, their interaction with the graphite surface is still the subject of current debate. This review paper presents relevant experimental data and results of selected theoretical calculations that, in time, guided the process of scientific discovery towards the current understanding of the alkali metals/graphite adsorption systems.

Exploding a wire on a metallic plate, we demonstrate reorganization of the metallic surface at different length scales. While optical microscopy shows clear concentric ring patterns, atomic force microscopy provide details of nanometre sized entities that constitute these rings. The size of these entities scales with the wire dimensions and applied explosion voltages. From fluctuations in the plasma current recorded during the process, the particle formation is seen to be a self-organization process.

We employ density functional theory to investigate the effect of hydrogen on TiN(111) surfaces and Al/TiN(111) interfaces. The results show that hydrogen atoms prefer to sit over different sites when adsorbing on the N- and Ti-terminated TiN(111) surfaces. Subsequent study shows that the work of adhesion of the hydrogen contaminated TiN(111) interface is substantially lower than that of the clean surface. A thorough analysis of the atomic structure and electronic density shows that hydrogen atoms break the original strong interfacial Al–N or Al–Ti bond of the clean surface and the new interfacial Al–H bond is rather weak. To gain insight into the tensile strength of the hydrogen contaminated interface, the tensile process is fully simulated. The different fracture behaviours are revealed for the clean interface and the hydrogen contaminated one: the fracture of the clean interface is ductile inside the Al slab, while that of the hydrogen contaminated interface is at the interface. Our calculated work of adhesion and tensile strength are quantitatively consistent with available theoretical and experimental results.

The optical properties of a silver film on soda-lime glass substrate were studied after treatment in different atmospheres at different temperatures. It has been shown that pre-treatment in air (at about 500 °C for 1 h) can induce the enhancement of the surface plasmon resonance (SPR) of silver nanoparticles after subsequent treatment in H₂. This enhancement effect decreases with decrease in the pre-treatment temperature in air up to 500 °C. Alternately heat-treating the as-prepared sample in air and then H₂ results in a continuous increase of the SPR. If the treatment temperature is at or above 600 °C, the SPR absorption can drastically be increased only by treatment in air without subsequent treatment in H₂. We can thus control the SPR intensity of the sample. A further experiment has revealed that the SPR is from the silver nanoparticles formed in the sublayer of the glass substrate. Pre-treatment in air is crucial to the formation of silver nanoparticles in the sublayer after subsequent treatment in H₂, which enhances the SPR.

Epitaxial growth processes for SiC polytypes in which a SiC substrate is employed are studied using a layered growth model. The corresponding phase diagrams of epitaxial growth processes are given. First-principles calculations are used to determine the parameters in the layered growth model. The layered growth phase diagrams show that when the rearrangement of atoms in one surface Si–C bilayer is allowed, the 3C-SiC structure is formed. When the rearrangement of atoms in two surface Si–C bilayers is allowed, the 4H-SiC structure is formed. When the rearrangement of atoms in more than two surface Si–C bilayers, excepting the case of five surface Si–C bilayers, is allowed, the 6H-SiC structure is formed, which is also shown to be the ground state structure. When the rearrangement of atoms in five surface Si–C bilayers is allowed, the 15R-SiC structure is formed. Thus the 3C-SiC phase would grow epitaxially at low temperature, the 4H-SiC phase would grow epitaxially at intermediate temperature and the 6H-SiC or 15R-SiC phases would grow epitaxially at higher temperature.

Lloyd's formula is an elegant tool to calculate the number of states directly from the imaginary part of the logarithm of the Korringa–Kohn–Rostoker (KKR) determinant. It is shown how this formula can be used at finite electronic temperatures and how the difficult problem to determine the physically significant correct phase of the complex logarithm can be circumvented by working with the single-valued real part of the logarithm. The approach is based on contour integrations in the complex energy plane and exploits the analytical properties of the KKR Green function and the Fermi–Dirac function. It leads to rather accurate results, which is illustrated by a local-density functional calculation of the temperature dependence of the intrinsic Fermi level in zinc-blende GaN.

The high-pressure photoluminescence of the LiTaO₃:Pr³⁺ system obtained for the pressure range from ambient to 232 kbar at 20 K and ambient temperatures is presented. The observed pressure red shift of all spectral lines representing the f–f transitions is related to the changes in F² Racach integral and the spin–orbit coupling with pressure. To analyse the deexcitation kinetics and the dependence of the intensity of the and on the excitation wavelength and pressure we propose a model of a Pr³⁺ trapped exciton with a hole localized at the Pr³⁺ and an electron at the Rydberg states bounded by the long-range Coulomb potential of the hole.

Resonant inelastic x-ray scattering (RIXS) at the L_2,3 edges of 3d transition metal compounds has recently become a high resolution spectroscopic technique thanks to improvements in the instrumentation. We have chosen the prototypical case of NiO to explore the various levels of interpretation applicable to L₃ RIXS spectra of strongly correlated electron systems. Starting from a set of experimental data measured across the Ni L₃ absorption edge with 550 meV combined energy resolution, we analyse the rich spectral structure within an atomic framework. The spectra can be separated into dd and charge transfer excitation regions. The dd excitations can be interpreted and well reproduced within a crystal field model. The charge transfer excitations are analysed through the comparison with calculations made in the Anderson impurity model. A series of parameters belonging to the proposed models (crystal field strength, charge transfer energy, hybridization integrals) can thus be extracted in a very direct and unambiguous way.

We derive an exact expression for the differential conductance for a quantum dot in an arbitrary magnetic field for small bias voltage. The derivation is based on the symmetric Anderson model using renormalized perturbation theory and is valid for all values of the on-site interaction U including the Kondo regime. We calculate the critical magnetic field for the splitting of the Kondo resonance to be seen in the differential conductivity as a function of bias voltage. Our calculations for small field show that the peak positions of the component resonances in the differential conductance are reduced substantially from estimates using the equilibrium Green function. We conclude that it is important to take the voltage dependence of the local retarded Green function into account in interpreting experimental results.

Resistivity measurements were carried out up to 8 GPa on single-crystal and polycrystalline samples of CeCu₂Si₂ from differing sources in the homogeneity range. The anisotropic response to current direction and small uniaxial stresses was explored, taking advantage of the quasi-hydrostatic environment of the Bridgman anvil cell. It was found that both the superconducting transition temperature T_c and the normal state properties are very sensitive to uniaxial stress, which leads to a shift of the valence instability pressure P_v and a small but significant change in T_c for different orientations with respect to the tetragonal c-axis. The coexistence of superconductivity and residual resistivity close to the Ioffe–Regel limit around 5 GPa provides a compelling argument for the existence of a valence fluctuation mediated pairing interaction at high pressure in CeCu₂Si₂.

We report the temperature and magnetic field dependence of resistivity, Hall effect, and thermopower of an La_0.85Ba_0.15MnO₃ single crystal. It is found that the Fermi level lies in the energy gap and conduction is by hopping. In the ferromagnetic state the variable range hopping prevails, while in the paramagnetic state hopping between nearest neighbours dominates. The small value of the activation energy of thermopower is explained by a weak asymmetry of density of states near the Fermi energy.

Thin films of ZnO agave-like nanowires were prepared on amorphous carbon thin layers on silicon substrates using thermal chemical vapour transport and condensation without any metal catalysts. The unusual superhydrophobicity of the fabricated surface was measured; the water contact angle reaches 151.1°. On the basis of experimental and theoretical analyses, it appears likely that the biomimetic microcomposite and nanocomposite surfaces of the prepared thin films of ZnO agave-like nanowires are responsible for the excellent superhydrophobicity.