Table of contents

It is shown that a density of states (DOS) proportional to the excitation energy, a so-called polar-like DOS, can arise in odd-parity states, with the superconducting gap vanishing at points even though the spin–orbit interaction for Cooper pairing is strong. Such gap structures are realized in the non-unitary states, F_1u (1, i, 0), F_1u (1, ε, ε²), and F_2u (1, i, 0), classified by Volovik and Gorkov (1985 Sov. Phys.–JETP61 843). This is due to the gap vanishing in a quadratic manner around a point on the Fermi surface.

It is shown that the unconventional nature of the superconducting state of PrOs₄Sb₁₂, a Pr based heavy electron compound with the filled-skutterudite structure, can be explained in a unified way by taking into account the structure of the crystalline-electric-field (CEF) level, the shape of the Fermi surface determined by the band structure calculation and a picture of the quasiparticles in the f ² configuration with a magnetically singlet CEF ground state. Possible types of pairing are narrowed down by consulting recent experimental results. In particular, the chiral 'p'-wave states such as p_x + ip_y are favoured under the magnetic field due to the orbital Zeeman effect, while the 'p'-wave states with twofold symmetry such as p_x can be stabilized by a feedback effect without the magnetic field. It is also discussed that the double superconducting transition without the magnetic field is possible due to the spin–orbit coupling of the 'triplet' Cooper pairs in the chiral state.

An Au nanoparticle/monolithic mesoporous silica assembly was synthesized by means of ultrasonic irradiation. For this as-prepared Au/silica sample, exposure to ambient air (or ageing) at room temperature (10°C) and subsequent drying at 120°C induce a new optical absorption at 460 nm in addition to the normal surface plasmon resonance (SPR) of Au nanoparticles. Further drying results in diminishing and even disappearance of this new peak accompanied by enhancement of the normal SPR. Further experiments revealed that the exposure to ambient air for sufficient time at room temperature after irradiation plays a crucial role in the appearance of the new peak after subsequent drying at 120°C. This new optical absorption peak may be associated with Au clusters with size less than 1 nm.

In this work we investigate quantum transport in Cu nanowires created by bringing macroscopic Cu wires into and out of contact under an applied magnetic field in air. Here we show that a 70% magneto-conductance effect can be seen in a Cu nanowire in a field of 2 mT at room temperature. We propose that this phenomenon is a consequence of spin filtering due to the adsorption of atmospheric oxygen modifying the electronic band structure and introducing spin-split conduction channels. This is a remarkable result since bulk Cu is not magnetic and it may provide a new perspective in the quest for spintronic devices.

Using Monte Carlo simulations and self-consistent field (SCF) theory we study the surface and interface properties of a coarse grained off-lattice model. In the simulations we employ the grand canonical ensemble together with a reweighting scheme in order to measure surface and interface free energies and discuss various methods for accurately locating the wetting transition. In the SCF theory, we use a partial enumeration scheme to incorporate single-chain properties on all length scales and use a weighted density functional for the excess free energy. The results of various forms of the density functional are compared quantitatively to the simulation results. For the theory to be accurate, it is important to decompose the free energy functional into a repulsive and an attractive part, with different approximations for the two parts.

Measuring the effective interface potential for our coarse grained model we explore routes for controlling the equilibrium wetting properties. (i) Coating of the substrate by an oxide layer gives rise to a subtle interplay between short-range and long-range forces, which may stabilize a film of mesoscopic thickness or result in the formation of nano-droplets. (ii) Coating the substrate with a polymer brush, we observe second-order wetting transitions at intermediate grafting densities, while the wetting transition is of first order at low and high grafting densities. In the latter limit, polymers of the same chemical structure as the brush do not wet the surface (autophobicity). (iii) Surface pattern (stripes) might give rise to unusual adsorption properties, which are related to morphological transitions. We relate our findings to experiments and discuss perspectives and limitations of the computational methods.

Vesicles constitute an interesting morphology formed by self-aggregating amphiphilic molecules. They exhibit a rich structural variety and are of interest both from a fundamental point of view (for studying closed bilayer systems) and from a practical point of view (whenever one is interested in the encapsulation of active molecules). In many circumstances vesicular structures have to be formed by external forces, but of great interest are amphiphilic systems, where they form spontaneously. Here the question arises of whether this means that they are also thermodynamically stable structures, which at least in some systems appears to be the case. If such vesicles are well defined in size, it is possible to pack them densely and thereby form vesicle gels that possess highly elastic properties even for relatively low volume fractions of amphiphile. Conditions for the formation and the microstructure of such vesicle gels have been studied in some detail for the case of unilamellar vesicles. Another important and topical issue is the dynamics of vesicle formation/breakdown, as the understanding of the transition process will open the way to a deeper understanding of their stability and also allow controlling of the structures formed, by means of their formation processes. Significant progress in the study of the transformation processes has been achieved, in particular by means of time-resolved scattering experiments.

Recent progress has been made in the understanding of the physical properties of chromatin—the dense complex of DNA and histone proteins that occupies the nuclei of plant and animal cells. Here I will focus on the two lowest levels of the hierarchy of DNA folding into the chromatin complex. (i) The nucleosome, the chromatin repeating unit consisting of a globular aggregate of eight histone proteins with the DNA wrapped around it: its overcharging, the DNA unwrapping transition, the 'sliding' of the octamer along the DNA. (ii) The 30 nm chromatin fibre, the necklace-like structure of nucleosomes connected via linker DNA: its geometry, its mechanical properties under stretching and its response to changing ionic conditions. I will stress that chromatin combines two seemingly contradictory features: (1) high compaction of DNA within the nuclear envelope and, at the same time, (2) accessibility to genes, promoter regions and gene regulatory sequences.

A review of the available tools for the calculation of the neutron double-differential cross-section of fundamental molecules, such as hydrogen and methane, is reported here. The most common cases occurring in neutron data analysis are treated in detail with the aim of providing the reader with intelligible and efficient procedures. The utility nowadays of these kinds of computation are widely described, and applications discussed, with examples based on the comparison with experimental data. New advances and refinement/corrections of earlier work are given throughout the paper, as well as suggestions for practical implementation.

Please note, a correction was made to this review (definition after equation (13)) on 10 November 2003

The Langevin equations of motion of the cage model of polar liquids originally proposed by Hill (1963 Proc. Phys. Soc.82 723) are solved for the first time for the particular case of rotation about a fixed axis, using a newly developed matrix continued fraction method. It is shown that the cage model predicts both the low-frequency Debye relaxation and a pronounced high-frequency (Poley) absorption peak in the far-infrared (FIR) region. The similarity of the equations of motion of the cage model to the equations which arise in the problem of generalizing the Onsager model of polar fluids to include a time-varying applied field suggests that the FIR (Poley) absorption may have its origins in the combined influence of molecular inertia and the torque due to the reaction field in the frequency-dependent version of the Onsager model. The complex susceptibility yielded by the cage model is shown to be in good agreement with experimental data on CH₃Cl that were taken as a typical example. Moreover, a simple approximate formula based on a small-oscillation approximation can describe accurately the dielectric spectra in most cases of interest.

We analyse here the thermodynamic behaviour of the thermal expansion coefficient for a number of liquids. The purpose of this work is to provide some general rules to develop equations of state models meeting the following criteria: thermodynamic consistency, generality, predictive power and accuracy to represent derived properties over wide ranges of pressure and temperature. The liquids included into our analysis have been selected to meet two criteria: (1) available experimental data over wide ranges of pressure and temperature (from the melting point up to the critical point), and (2) liquids composed of molecules with different geometries and interactions.

The spinodal is a locus in the P–V diagram, which is the limit of metastability of a substance with respect to a phase transition. In particular, it is the limit to the negative (tensile) pressure exerted on a liquid, at which the liquid may still be metastable with respect to the gas phase. By requiring that the Helmholtz free energy should be analytic at the spinodal, it is possible to derive the limiting behaviour of thermodynamic properties near the spinodal. In the present paper we show how this analyticity requirement may be used to choose between available equations of state (EOSs). In particular it is shown that the universal equation of state (UEOS) proposed by Vinet et al, complies with the analyticity requirement and may be used to locate the spinodal by extrapolation from within the stable region. The Baonza or 'pseudospinodal' EOS, which is apparently based on the functional form of thermodynamic properties near the spinodal, actually contradicts the analyticity requirement and indeed yields manifestly wrong results in locating the spinodal. However it is shown that the Baonza equation may be viewed as an approximation to the UEOS in states of compression. Its technical importance, which stems from its algebraic simplicity, is also stressed in the present work.

The hydrodynamic interaction between a colloidal particle attached to the tip of an atomic force microscope (AFM) and a wall has been investigated as a function of the angle of inclination of the cantilever with respect to the surface. For high inclination of the cantilever, the motion mostly occurs in the tangential direction. A frequency-dependent drag coefficient is extracted from the cantilever's Brownian motion. In agreement with theoretical predictions, the wall-induced drag for tangential motion is much weaker than that for vertical motion. Mechanical properties of the surface are more easily probed with tangential motion because the hydrodynamic effects do not mask the surface's intrinsic properties as much as for vertical motion.

Structural transitions in a single AB-copolymer chain where saturating bonds can be formed between A-and B-units are studied by means of Monte Carlo computer simulations using the bond fluctuation model. Three transitions are found, coil–globule, coil–hairpin and globule–hairpin, depending on the nature of a particular AB-sequence: statistical random sequence, diblock sequence and 'random–complementary' sequence (one-half of such an AB-sequence is random with Bernoulli statistics while the other half is complementary to the first one). The properties of random–complementary sequences are closer to those of diblock sequences than to the properties of random sequences. The model (although quite rough) is expected to represent some basic features of real RNA molecules, i.e. the formation of secondary structure of RNA due to hydrogen bonding of corresponding bases and stacking interactions of the base pairs in helixes. We introduce the notation of RNA-like copolymers and discuss in what sense the sequences studied here can be considered as RNA-like copolymers.

Electron transport and magnetic properties of three series of manganates of the formula (La_1−xLn_x)_0.7Ca_0.3MnO₃ with Ln = Nd, Gd and Y, wherein only the average A-site cation radius ⟨r_A ⟩ and associated disorder vary, without affecting the Mn⁴⁺/Mn³⁺ ratio, have been investigated in an effort to understand the nature of phase separation. All three series of manganates show saturation magnetization characteristic of ferromagnetism, with the ferromagnetic T_c decreasing with increasing x up to a critical value of x, x_c (x_c = 0.6, 0.3, 0.2 respectively for Nd, Gd, Y). For x > x_c, the magnetic moments are considerably smaller, showing a small increase around T_M, the value of T_M decreasing slightly with increase in x or decrease in ⟨r_A ⟩. The ferromagnetic compositions (x ≤ x_c) show insulator–metal transitions, while the compositions with x > x_c are insulating. The magnetic and electrical resistivity behaviour of these manganates is consistent with the occurrence of phase separation in the compositions around x_c, corresponding to a critical average radius of the A-site cation, ⟨r_A^c ⟩, of 1.18 Å. Both T_c and T_IM increase linearly when ⟨r_A ⟩ > ⟨r_A^c ⟩ or x ≤ x_c, as expected of a homogeneous ferromagnetic phase. Both T_c and T_M decrease linearly with the A-site cation size disorder as measured by the variance σ². Thus, an increase in σ² favours the insulating AFM state. Percolative conduction is observed in the compositions with ⟨r_A ⟩ > ⟨r_A^c ⟩. Electron transport properties in the insulating regime for x > x_c conform to the variable-range hopping mechanism. More interestingly, when x > x_c, the real part of dielectric constant (ε') reaches a high value (10⁴ –10⁶) at ordinary temperatures dropping to a very small (∼ 500) value below a certain temperature, the value of which decreases with decreasing frequency.

We consider a new type of magnetic tunnel junction, which consists of two ferromagnetic tunnel barriers acting as spin filters (SFs), separated by a nonmagnetic metal (NM) layer. Using the transfer matrix method and the free-electron approximation, the dependence of the tunnel magnetoresistance (TMR) on the thickness of the central NM layer, bias voltage and temperature in the double SF junction are studied theoretically. It is shown that the TMR and electron-spin polarization in this structure can reach very large values under suitable conditions. The highest value of the TMR can reach 99%. By an appropriate choice of the thickness of the central NM layer, the degree of spin polarization in this structure will be higher than that of the single SF junctions. These results may be useful in designing future spin-polarized tunnelling devices.

A novel ternary structure type has been determined from single crystals of Ce₂Zn₆Ge₃ grown from indium–zinc flux solvent. The Ce₂Zn₆Ge₃ type is hexagonal (a = 0.767 69(2) nm; c = 0.411 59(2) nm) with space group P 2m, Z = 1. Isotypic compounds with La, Pr, Nd, Sm and Gd were synthesized by reaction sintering, and their isotypic crystal structures were confirmed from Rietveld refinements. These novel ternaries show metallic behaviour and their ground state depends on the particular rare earth ion. Long-range magnetic order was deduced for the compounds from Ce to Gd, with a maximum transition temperature T_N ∼ 29 K for Gd₂Zn₆Ge₃. While the compounds with Ce and Pr exhibit a spontaneous magnetic type of order, those with Nd, Sm and Gd are antiferromagnetic. The magnetic structures of Pr₂Zn₆Ge₃ and Nd₂Zn₆Ge₃ were resolved on the basis of neutron powder diffraction performed at 1.5 K.

Structural and dielectric characterizations of the relaxor ferroelectric PbZn_1/3Nb_2/3O₃ (PZN) were carried out on single crystals in the temperature range of the dielectric anomaly (370 K < T < 440 K), under dc electric field applied along [001]-and [111]-directions. Two ferroelectric phases, tetragonal (T) and rhombohedral (R), can be field induced in this temperature range, the symmetry of which depends on the direction of the applied field, [001] and [111] respectively. E–T diagrams were built and interpreted under the consideration of polar nano-regions (PNRs) with a prominent tetragonal component. These PNRs prevent the onset of a monodomain state when the field is applied along [111] and explain the features of PZN for an applied field along [001]: large lattice strain, easy onset of the T phase and suppression of the dielectric relaxation for E^≥ 1.5 kV cm⁻¹. The microscopic origin of these PNRs can be discussed in relation with recent nuclear magnetic resonance and structural results reported in other isomorphous relaxors.

The structural and electronic properties of the Li_1+xV₃O₈ insertion electrode, where 0 ^≤x < 0.4, have been explored by means of x-ray four-circle diffraction and through measurements of electrical resistivity, thermoelectric power, magnetization and electron paramagnetic resonance. Detailed structure refinements for x = 0.06 and 0.29 reveal the preferential and partial reduction of V ions which may give rise to low-dimensional electronic properties. The composition with x = 0 exhibits a quasi-one-dimensional polaronic transport in the localized states of band tails due to the slight deficiency of oxygen atoms. For x > 0.1 with nearly stoichiometric oxygen atoms, small polarons exist without carrier-creation energy at high temperatures, while at low temperatures the conduction may be of variable-range hopping (VRH) type. For x > 0.2, one-dimensional magnetic properties appear due to sizable exchange couplings and order–disorder effects of additional Li ions may lead to significant change of transport properties. For the intermediate composition 0 < x^≤ 0.1, strong randomness of the Li doping and the congenital oxygen deficiency cause VRH states even at high temperatures.

Results of polarized neutron diffraction on the compound CeB₆ are used to obtain its magnetization density distribution. The measurements are performed at two different points of the magnetic phase diagram (phase I and II). The data are analysed in direct space using the maximum entropy method, as well as in reciprocal space using the cerium form factor expansion and anisotropy. The conclusion is that, in both phases, the magnetization is localized on the cerium sites only. This result is in contradiction to a recent paper by Saitoh et al (2002 J. Phys. Soc. Japan71 2369), claiming that, in phase II, a localized spin moment was observed at non-atomic sites.

We investigate the phase behaviour of binary symmetric lattice fluid, exhibiting partial demixing in slitlike pores with heterogeneous walls. The calculations are carried out assuming a cubic lattice with vacancies and a model for heterogeneity similar to that of Röcken and Tarazona (1996 J. Chem. Phys.105 2034). We concentrate on the effects of surface heterogeneity on the scenarios for the phase transformations. It is shown that for wide enough pores a step-wise condensation occurs between demixed phases. For narrower pores the λ-line may cross the boundaries of the bridge phase and multiple critical end points appear. In such cases, at low temperatures the bridge phase formation occurs between demixed phases, at intermediate temperature it involves mixed and demixed phases and finally it becomes a transition between two demixed phases again.

High-pressure polymorphs of WO₃ have been studied with a first-principles pseudopotential method. The medium-range (0.01–20 GPa) and high-range (20–30 GPa) polymorphs have been characterized and are compared with recent experimental results. The main new feature is the appearance of a sevenfold coordinated tungsten in the high-pressure polymorph. The subtle phase transitions that were induced from Raman spectra evolutions have not been confirmed. However, changes in the W–O distances and O–W–O and W–O–W angles may explain the changes in Raman spectra.

The single substitutional nitrogen atom in diamond is apparently a very simple defect in a very simple elemental solid. It has been modelled by a range of computational models, few of which either agree with each other, or with the experimental data on the defect. If the computational models of less well understood defects in this and more complex materials are to be reliable, we should understand why the discrepancies arise and how they can be avoided in future modelling. This paper presents an all-electron, augmented plane-wave (APW) density functional theory (DFT) calculation using the modern APW with local orbitals full potential periodic approximation. This is compared to DFT, finite cluster pseudopotential calculations and a semi-empirical Hartree–Fock model. Comparisons between the results of these and previous models allow us to discuss the reliability of computational methods of this and similar defects.

Raman scattering spectra of a set of lithium manganospinels Li_1−x+zMn_2−zO₄ with 0 ^≤x^≤ 1 and 0 ^≤z^≤ 0.33 are reported and analysed. Structural changes have been investigated following the evolution of Raman spectra with the concentration of lithium cations. The local structure was characterized as a function of the mean oxidation state of manganese cations. The trigonal distortion of MnO₆ octahedra is evidenced by insertion of lithium ions into the [B₂]O₄ spinel framework. A comparison with tetragonal Mn₃O₄ and Fe₃O₄ spinels shows the influence of the Jahn–Teller effect on the Raman features for this class of materials.

Sharp absorption lines produced by hydrogen in diamond have been studied in diamonds grown from ¹³C by high-pressure, high-temperature synthesis. Analyses of the two-phonon intrinsic absorption and of the Raman shift have shown that the ¹²C content of the diamond is 13.5%. This value is entirely consistent with the relative intensities of the absorption lines at 3107 and 3098 cm⁻¹, confirming that they are due to a strongly localized C–H stretching vibration. A correlated line, observed at 1405 cm⁻¹ for natural diamond, and attributed to the C–H bending vibration, exhibits both an isotope shift and a shift due to weak coupling with the one-phonon modes. By analogy with natural diamond, lines for the ¹³C diamond at 2757 and 4469 cm⁻¹ are assigned to the combinations 2ℏω_b and ℏω_s + ℏω_b, respectively, where ℏω_s and ℏω_b are the stretch and bend frequencies. The frequency invariance, on carbon isotope substitution, of a hydrogen-related line at 3237 cm⁻¹ is not inconsistent with the proposal that this is produced by a N–H vibration.

In this work, x-ray propagation in microsize and nanosize capillaries has been considered in the framework of a simple unified wave theory. It is shown that diminishing of the channel sizes completely changes the mode of beam transportation; that is, we obtain the transformation of surface channelling in microcapillaries to bulk channelling in nanocapillaries (nanotubes).

The electronic structure of Fe-diluted Au–Fe alloys has been studied by taking core-level and valence-band spectra using x-ray photoemission spectroscopy and synchrotron radiation. From the core-level spectroscopy, we found that the Fe 2p spectrum is composed of d⁶ and d⁷ multiplets from Fe impurity atoms. This behaviour is qualitatively discussed within the context of electron–electron interaction. In order to explore the electron-correlation effects in the valence band, we obtained Fe 3d partial spectral weights by taking advantage of the Cooper-minimum phenomenon of an Au 5d photoionization cross section. It was found that the spin-down states have an appreciable amount of spectral weights throughout the host Au 5d band, contrary to previous one-electron calculations predicting two-peak structure of the Fe 3d states. We suggest that this discrepancy results from the correlation effect of the Fe 3d electrons.

We have performed photoemission spectroscopy of Ni–Pt alloys to understand the origin of the discrepancy between the experimental linear coefficient of specific heat γ and that predicted by band theory. We found that the quasiparticle density of states at the Fermi level deduced from photoemission measurement is in agreement with the experimental value of γ, if we include the electron correlation effect. It was also found that the Ni 2p core level satellite intensity increases as Ni content is reduced, indicating a strong electron correlation effect which can enhance the quasiparticle effective mass considerably. This supports our conclusion that electron correlation is the most probable reason of disagreement of γ between experiment and band theory.

The optical properties of the ordered defect compound  CuIn₃Te₅ which crystallizes in a chalcopyrite-related structure have been studied by absorption and photoluminescence (PL) techniques. Optical absorption measurements show that the band gap energy E_G varies from 1.078 to 1.040 eV between 10 and 300 K. It is found that the variation of E_G with temperature is mainly due to the contribution of optical phonons with a characteristic energy of about 16 meV. The PL measurements, carried out between 4 and 100 K with laser excitation intensities in the range from 1 to 400 mW, reveal that the main PL band is due to a donor–acceptor recombination between donor and acceptor defect levels that have activation energies of 60 and 30 meV, respectively. These donor and acceptor states are tentatively assigned as originating from indium atoms on copper sites and copper vacancies, respectively.

We study two correlated electrons in a nearest-neighbour tight-binding chain, with both on-site and nearest-neighbour interaction. Both the cases of parallel and antiparallel spin are considered. In addition to the free electron band for two electrons, there are correlated bands with positive or negative energy, depending on whether the interaction parameters are repulsive or attractive. Electrons form bound states, with amplitudes that decay exponentially with separation. Conditions for such states to be filled at low temperatures are discussed.

On the basis of the Mott criterion for metal–insulator transition (MIT), an expression for the correlation length, identical to that for the coherence length in the theory of superconductivity, is obtained. This correlation length characterizes the size of an electron–hole pair (in an excitonic insulator) or the effective Bohr radius (as, e.g., in doped semiconductors). The relation obtained is used for calculation of the coherence length in vanadium dioxide. The presence of two characteristic coherence lengths (ξ₁ ∼ 20 Å and ξ₂ ∼ 2 Å) is found. This is associated with the specific features of the transition mechanism in VO₂: this mechanism represents a combination of the purely electronic Mott–Hubbard contribution and the structural (Peierls-like) one. It is shown, however, that the driving force of the MIT in VO₂ is the electron-correlation Mott–Hubbard transition.

A theory describing multiphonon resonant Raman scattering (MPRRS) processes in wide-gap diluted magnetic semiconductors is presented, with Cd_1−xMn_xTe as an example. The incident radiation frequency ω_l is taken above the fundamental absorption region. The photoexcited electron and hole make real transitions through the LO phonon, when one considers Fröhlich (F) and deformation potential (DP) interactions. The strong exchange interaction, typical of these materials, leads to a large spin splitting of the exciton states in the magnetic field. Neglecting Landau quantization, this Zeeman splitting gives rise to the formation of eight bands (two conduction and six valence ones) and ten different exciton states according to the polarization of the incident light. Explicit expressions for the MPRRS intensity of second and third order, the indirect creation and annihilation probabilities, the exciton lifetime, and the probabilities of transition between different exciton states and different types of exciton as a function of ω_l and the external magnetic field are presented. The selection rules for all hot exciton transitions via exciton–photon interaction and F and DP exciton–phonon interactions are investigated. The exciton energies, as a function of B, the Mn concentration x, and the temperature T, are compared to a theoretical expression. Graphics for creation and annihilation probabilities, lifetime, and Raman intensity of second and third order are discussed.

Elementary electronic excitation is studied theoretically for a two-dimensional electron gas in the presence of spin–orbit (SO) interaction induced by the Rashba effect. We find that in such a system, coupled plasmon–phonon excitation can be achieved via intra- and inter-SO electronic transitions. As a result, six branches of the coupled plasmon–phonon oscillations can be observed. The interesting features of these excitation modes are analysed.

The crystal fields (CFs) of the binary rare-earth compounds PrAl₃ and NdAl₃ have been examined at ambient pressure by means of inelastic neutron scattering. The CF of the latter compound has also been measured under hydrostatic pressure (p = 0.84 GPa). The observed substantial changes of the CF under pressure are discussed within the framework of first-principles density functional theory calculations.

We present the basic system of equations for a theory of superconductivity for systems with chaotically distributed paramagnetic impurities of substitution in which the Migdal theorem is violated (it cannot be supposed ω₀ ≪ E_F ). We take into account electron–phonon and impurity diagrams as well as supplementary ones corresponding to the intersection of electron–phonon and electron–impurity lines. Decrease of the quantity T_C with increase of impurity concentration is shown to weaken in comparison with the case of the usual superconductors. The degree of this decrease is determined by quantities m and q_c. The coefficient of the isotope effect α, energy gap and order parameter at T = 0 are also calculated. The behaviour of these quantities as a function of impurity concentration depends on the Migdal parameter m = ω₀ /E_F and transferred momentum q_c.

The effects on the magnetization of fluctuating Cooper pairs created above the superconducting transition by thermal agitation energy (the so-called fluctuation-induced diamagnetism, FD) have been measured in a clean type I superconductor (Pb) and in a clean low Ginzburg–Landau parameter (κ) type II superconductor (Nb). These experiments extend the earlier measurements of Gollub, Beasley and Tinkham to both the high reduced temperature region (ε ≡ ln (T/T_C0) ≳ 0.1) and the high reduced magnetic field region (h ≡ H/H_C2 (0) ≳ 0.1). Our data show that in spite of FD being deeply affected in both superconductors by the presence of non-local electrodynamic effects, the superconducting fluctuations sharply vanish when ε or h become of the order of 0.5 and, respectively, 1. This short-wavelength behaviour at high reduced temperatures of the superconducting fluctuations is similar to that previously observed at high reduced temperatures in dirty low-T_C superconductors and in high-T_C cuprates, where the non-local effects are unobservable. These last results suggest that in the short wavelength regime the superconducting fluctuations in clean low-T_C superconductors are still dominated by the uncertainty principle, which imposes a limit to the shrinkage, when ε increases, of the superconducting wavefunction. This may also be the case when h → 1, although the presence of strong non-local effects in these clean and low-κ superconductors may also deeply affect their high field behaviour.

A large change in the magnetic entropy, |ΔS|, was observed in the Fe-based NaZn₁₃-type compound LaFe_11.375Al_1.625, which was nearly temperature independent over a wide temperature range (an about 70 K span from ∼ 140 to 210 K). This behaviour of the magnetic entropy change is associated with two closely spaced magnetic transitions. X-ray diffraction investigation at different temperatures indicates that the crystal structure remains cubic, of NaZn₁₃ type, when the magnetic state changes with temperature, but the cell parameter changes dramatically at the first-order transition point.

Single crystals of EuCu₂Ge₂ were grown and characterized using electrical resistivity, magnetization, specific heat and magnetoresistance measurements. The crystals exhibit antiferromagnetic transitions at T_N1 = 9 K and T_N2 = 5 K. The T_N of the flux-grown single crystals reported here are lower than that reported for the polycrystalline sample (T_N = 13 K) in the literature (Felner and Nowik 1978 J. Phys. Chem. Solids39 763). The magnetoresistance is positive in the ordered state and negative in the paramagnetic state. The magnetic order could not be suppressed up to a pressure of 25 kbar.

The formation, crystal structure and magnetic properties of Sm₂Fe_17−xCo_xC_y were studied. The substitution of Co for Fe helps to stabilize the rhombohedral Th₂Zn₁₇-type structure (2:17) and eliminate α-Fe formation for carbon concentrations y^≤ 1.5. From the mixing enthalpy calculations based on Miedema's semi-empirical model and Wigner–Seitz cell analysis, it is found that the role of Co in stabilizing the 2:17 structure is related to its strong preference for the 18h site, which has a maximum number of rare-earth near neighbours in the structure. With increasing Co content, x, the lattice constants decrease while the Curie temperature rapidly increases. The typical compound Sm₂Fe₁₂Co₅C_1.25 has a room temperature saturation magnetization μ₀M_s = 1.36 T, a magnetic anisotropy field μ₀H_k = 7.1 T, a Curie temperature T_C = 874 K and a possible maximum operating temperature T_m higher than 473 K.

For Ce³⁺, Er³⁺ and Yb³⁺ ions, electron paramagnetic resonance (EPR) spectra typical for S' = 1/2 ions are measured for YAl₃(BO₃)₄ (YAB) single crystal. The spectra show axial symmetry indicating that all three dopants replace Y³⁺ at the given dopant concentration. Corresponding - and hyperfine Ã-tensors are determined. The EPR linewidth of Ce broadens with increasing temperature due to an Orbach relaxation process. Fitting the curve with an exponential, the energy difference is found to be equal to 270 ± 16 cm⁻¹.

The optical absorption and excitation spectra of Ce in YAB single crystal measured at 300 K are similar to those found for polycrystalline materials. High-resolution polarized emission from the lowest excited to the ² F _5/2 ground state, measured at 4.2 K, indicates a splitting of the ground state into three levels. The second level is located 277 ± 18 cm⁻¹ above the first one, in excellent agreement with the EPR result, and the third level is located 140 ± 10 cm⁻¹ above the second one.

We report on polarized Raman scattering of single crystals of Nd_1−xSr_xMnO₃ (x = 0.3, 0.5). Raman spectra of Nd_0.7Sr_0.3MnO₃ show a significant change through the metal–insulator transition. In the ferromagnetic metallic phase phonon modes grow in intensity and number while the electronic continuum becomes more pronounced. We suggest that these effects are due to the strong competition between the localization and the delocalization of carriers which is the origin of the largest colossal magnetoresistance effect ever reported for the manganites. Raman spectra of Nd_0.5Sr_0.5MnO₃, upon cooling through the charge-ordering temperature T_CO = 148 K, exhibit several new lines which undergo a substantial hardening. This hardening is interpreted as a freezing of the Jahn–Teller distortions with a gradual decrease of a fraction of the ferromagnetic phase in the CE-type charge/orbital ordered state.

Photoreflectance (PR) spectra of two type II [001](GaAs)_m(AlAs)_n superlattices (SLs) have been measured at 77 K. In the conventional picture of the envelope-function approximation, the lowest conduction state originates, in the first sample, from the X_z point of the AlAs Brillouin zone (z being the growth direction) whereas it originates from the X_x,y point in the second sample. Our spectra exhibit Franz–Keldysh oscillation (FKO) features and interband transition lines. The origin of the built-in electric field within the samples is discussed and its strength calculated from FKOs. For interpreting our spectra of interband optical transitions, a least-squares fit of the data to the Aspnes third-derivative functional form has been performed as well as computation of the optical transition energies. From the energy and amplitude of the interband transition lines in PR spectra, we showed that the two SLs are pseudo-direct, i.e. the ground optical transition in any of them is direct in the k space and takes place at the Γ point of the SL Brillouin zone. All the other interband transitions appearing in the SL spectra are also direct in k space.

The dewetting of thin polymer films on solid substrates has been studied extensively in recent years. These films can decay either by nucleation events or by spinodal dewetting, essentially only depending on the interface potential describing the short- and long-range intermolecular interactions between the interfaces and the initial film thickness. Here, we describe experiments and simulations concerned with the decay of polystyrene thin films. The rupture of the film occurs by the formation of a correlated pattern of holes ('satellite holes') along the liquid rims accumulating at the channel borders. The development of this complex film rupture process, which is neither simply spinodal nor nucleation dewetting, can be mimicked precisely by making use of a novel simulation code based on a rigorous mathematical treatment of the thin film equation and on the knowledge of the effective interface potential of the system. The conditions that determine the appearance and the position of the satellite holes around pre-existing holes are discussed.