Table of contents

The Landauer formula for dissipationless conductance lies at the heart of modern electronic transport, yet it remains without a clear microscopic basis. We analyse the Landauer formula microscopically and give a straightforward quantum kinetic derivation for open systems. Some important experimental implications follow. These lie beyond the Landauer result as popularly received.

The optical properties of Co/Cu multilayers are investigated theoretically using a multiband tight-binding model and the results are compared to experimental data on the magneto-refractive effect (MRE). The optical conductivity of both parallel and antiparallel configurations of Co/Cu multilayers is calculated using the Kubo–Greenwood formula. The Kramers–Kronig relations are utilized to obtain the imaginary part of the conductivity and the real part of the dielectric function. The conductivity is decomposed into the intraband and interband terms, so that their different contributions to the MRE may be analysed. In particular, we find that the competition between the intraband and interband contributions leads to a change of sign in the MRE as a function of frequency, a feature which is also observed experimentally in the infrared region. This is in contrast to the predictions of the Drude model, where only the intraband part of the conductivity is considered and the MRE curve always takes the same sign. Therefore, it is vital to include the interband contribution for a full spectral study of the origin of the infrared MRE data.

Recently it was suggested that tetrahedral liquids such as water and silicon exhibit a fragile-to-strong transition while approaching the glass-transition temperature (T_g). Such a drastic change in the fragility of liquid as a function of temperature is very rarely observed. Here we propose that, contrary to the popular fragility transition scenario, this phenomenon should be explained in terms of the crossover from a non-glass-forming to a glass-forming branch. For ordinary glass-forming liquids, there is frustration between long-range density ordering (crystallization) and short-range bond ordering (energetic frustration hidden in the interaction potential), which helps vitrification. For water and silicon, such frustration does not exist near the melting point (T_m) at ambient pressure since the symmetry of their crystals is consistent with that of short-range tetrahedral bond ordering. Thus, we call this high-temperature region near T_m a non-glass-forming branch. In the low-temperature region near T_g, which we call a glass-forming branch, on the other hand, a system tends to have long-range density ordering. Its competition with local tetrahedral ordering induces strong frustration effects, which make the liquid strong. Our scenario suggests that the crossover from a non-glass-forming to a glass-forming branch may be generic to tetrahedral liquids whose specific volume increases upon crystallization.

The anomalous properties of cold and supercooled water, such as the fact that at sufficiently low temperatures it becomes more compressible and less dense when cooled, and more fluid when compressed, have attracted the attention of physical scientists for a long time. The discovery in the 1970s that several thermodynamic and transport properties of supercooled water exhibit a pronounced temperature dependence and appear to diverge slightly below the homogeneous nucleation temperature inspired a large number of experimental and theoretical studies. Likewise, an important body of work on glassy water has been stimulated by experiments, starting in the mid-1980s and continuing to this date, which suggest that vitreous water can exist in at least two apparently distinct forms. A coherent theory of the thermodynamic and transport properties of supercooled and glassy water does not yet exist. Nevertheless, significant progress towards this goal has been made during the past 20 years. This article summarizes the known experimental facts and reviews critically theoretical and computational work aimed at interpreting the observations and providing a unified viewpoint on cold, non-crystalline, metastable states of water.

The glass transition, crystallization, apparent activation energy and glass forming ability (GFA) of a metallic glass as well as their correlations were studied in amorphous alloys of composition Fe_91−xB_xZr₅Nb₄ (FBZN, at.%) and Fe_61−xCo_xZr₅B₃₀Nb₄ (FCZBN, at.%). It was found that the glass transition temperature T_g and the crystallization temperature T_x can be related by a formula, T_x = αT_g+β, for each amorphous alloy in the two systems. α and β are constants for a given amorphous alloy, obtained by making measurements using non-isothermal scanning at various heating rates in a differential scanning calorimeter and then applying Lasocka's equation. The apparent activation energy of the glass transition E_g was observed to be directly proportional to α and have a correlation, E_g = 3.527(T_x−β)/T_g+1.09, with T_x and T_g. The supercooled liquid region ΔT_x, which is used for characterization of the GFA, is related to E_g and T_g by the formula ΔT_x = (E_g/3.527− 1.309)T_g+β.

The mobility of water molecules confined in a silica pore is studied by computer simulation in the low hydration regime, where most of the molecules reside close to the hydrophilic substrate. A layer analysis of the single particle dynamics of these molecules shows an anomalous diffusion with a sublinear behaviour over a long period. This behaviour is strictly connected to the long time decay of the residence time distribution analogous to water in contact with proteins.

The high-pressure and high-temperature phase diagram of Ta has been studied in a laser-heated diamond-anvil cell (DAC) using x-ray diffraction measurements up to 52 GPa and 3800 K. The melting was observed at nine different pressures, the melting temperature being in good agreement with previous laser-heated DAC experiments, but in contradiction with several theoretical calculations and previous piston–cylinder apparatus experiments. A small slope for the melting curve of Ta is estimated ( at 1 bar) and a possible explanation for this behaviour is given. Finally, a P–V–T equation of states is obtained, the temperature dependence of the thermal expansion coefficient and the bulk modulus being estimated.

Low-frequency light scattering spectra of As₂S₃ glass former have been investigated over a temperature range of 300–712 K. Using the model of a damped oscillator, the parameters of the intensities of the boson peak and of the fast relaxation as well as the boson peak position and the relaxational time are extracted as a function of temperature. The temperature increase of the fast relaxation becomes more sharp above T_g and stabilizes at T = 600 K. By analogy with other glass formers it is suggested that the critical temperature T_c within the framework of the mode-coupling theory should be near 600 K for As₂S₃. It was found that the damping parameter at T_c is the same for As₂S₃ and B₂O₃; an explanation of this coincidence is suggested. The boson peak is found to be present up to 712 K with almost the same strength as at low temperatures.

The thermal stability of nanocrystalline ultrasoft magnetic (Fe₉₈Zr₂)_1−xN_x films with x = 0.10–0.25 was studied using thermal desorption spectrometry, positron beam analysis and high resolution transmission electron microscopy. The results demonstrate that grain growth during the heat treatment is accompanied by an increase of the free volume and nitrogen relocation and desorption. All these phenomena can drastically degrade the ultrasoft magnetic properties. The nitrogen desorption has already started at temperatures around 400 K. Nevertheless, most of the nitrogen leaves the sample at a temperature above 800 K. We found that nitrogen out-diffusion is significantly retarded compared with the prediction of the diffusion in bulk α-Fe. A qualitative model is proposed in which the nitrogen out-diffusion in nanocrystalline material is retarded by trapping at immobile defects, namely Zr atoms, and also by voids at grain boundaries. From a certain temperature, nitrogen migrates from the interior of the nanograins to the nanovoids at the grain boundaries and the out-diffusion to the outer surface is controlled by transport between the voids.

The distribution of the local density of states (LDOS) in quasiperiodic photonic crystals (QPCs) and the total density of states (DOS) are studied. The distribution of the LDOS shows that it has the same rotational symmetry as the sample. Furthermore, the regions of lowest LDOS and the change of the minimal values of the LDOS with the alteration of the dielectric volume fractions are identified. Meanwhile, the coincidence of gaps displayed in transmission and DOS spectra indicates that QPCs possess absolute gaps for TM polarized modes, the E field is along the axis of the cylinders and the H field is in the 2D plane.

We report calculations of oscillator strengths for the far infrared absorption of light by the excitonic complexes Xⁿ⁻ (the excess charge, n, ranging from one to four) confined in quantum dots. The magnetic field is varied in an interval which corresponds to 'filling factors' between 2 and 3/5. Electron–hole interaction effects are seen in the deviations of the peak positions from the Kohn lines, and in the spreading of the oscillator strengths over a few final states. Transition densities are used as an additional tool to characterize the absorption peaks.

A quantitative characterization of residual stresses was performed with a nanometric spatial resolution in Er/Ge-doped silica glass fibres. Stresses were assessed by a piezo-spectroscopic technique (i.e., monitoring wavelength shifts), which used the electro-stimulated luminescence of optically active defects in silica glass. Residual stresses of GPa magnitude were found near the core/cladding interface by using a nanometre-sized electron probe. Diffusion of Er/Ge ions from the core towards the cladding area was clearly observed in this optical device and the occurrence of this diffusive phenomenon permitted stress measurement in extended cladding regions beyond the core/cladding interface. A discussion is given of the impact of residual stresses on the optical performance of the fibre device.

Using electrically- and laser-heated diamond anvil cells at pressures above 40 GPa we synthesized the pure high-pressure Fe₃O₄ phase (h-Fe₃O₄)and performed an in situ structural refinement. In good agreement with our ab initio calculations we found that h-Fe₃O₄ adopts the CaTi₂O₄-type structure (space group Bbmm). Electrical resistivity measurements show that h-Fe₃O₄ is metallic up to at least 70 GPa.

Zirconium oxide thin films were grown on n-Si(100) and quartz substrates by using an off-plane filtered cathodic vacuum arc without external heating. A Zr cathode was used to obtain the plasma and the deposition rate was varied from 75 to 35 nm min⁻¹ corresponding to various oxygen flow rates. Optical properties of as-deposited films are presented as a function of oxygen flow rate and shown to depend greatly on it. The transmittance and optical band gap (E_g) increase with the oxygen flow rate whereas optical constants decrease. Film optical homogeneity is considerably enhanced and good homogeneity is exhibited for the films deposited at oxygen flow rate above 50 sccm. Structural homogeneity remains throughout the film depth even though the respective film structure changes with the different oxygen flow rates. Bulk-like stoichiometric amorphous zirconium oxide film exhibits high E_g (5.0 eV), high transmittance and good optical constants (high refractive index of 2.16 at 550 nm and low extinction coefficient of at 550 nm) with homogeneous structure.

Acoustic properties of the transparent relaxor ferroelectric ceramics of PLZT-10/65/35 and PLZT-7.6/72/28 were studied by the high-resolution micro-Brillouin scattering technique. The ceramics showed significant softening in the elastic constant and velocity of the longitudinal acoustic (LA) phonon mode, a broad anomaly in the attenuation of the LA mode, and a frequency-dependent dielectric maximum. The temperature dependences of the acoustic anomalies could be explained qualitatively by using electrostrictive coupling, quadratic in order parameter and linear in strain. The interaction between the polar micro regions is more pronounced at some percolation limit below the Burns temperature T_B, where the shear deformation develops due to polarization fluctuations, local electrostrictive strain fields and tilting of the oxygen octahedra.

The pressure-induced martensitic transition of magnesium from the ground-state hexagonal-close-packed (hcp) structure at atmospheric pressure to a body-centred-cubic (bcc) structure at hydrostatic pressures larger than about 500 kbar is studied with the full-potential, linearized, augmented-plane-wave method. At any given value of the pressure, the minimum in the Gibbs free energy G, which gives the equilibrium structure, is found from the values of G along the epitaxial Bain path. This procedure, when repeated for several pressure values, allows the determination of the pressure dependence in the equilibrium state of the free energy, the volume per atom, the lattice parameters and the axial ratio for both the hcp and the bcc structures. The transition pressure is determined by the crossing of the free energies as functions of pressure for the hcp and bcc phases. The second strain-derivative of G at equilibrium at each pressure determines the elastic constants. For the shear constants c₄₄ and c₆₆ of the hcp structure, the internal relaxation of the second basis atom is taken into account. The elastic constants and c₄₄ of bcc magnesium are positive and increase with pressure.

The resistivity minimum in manganites is still under debate. Recent publications discussed two possible scenarios: (i) electron–electron interaction in weak disordered systems and (ii) charge carriers tunnelling between antiferromagnetic coupled grains. In order to resolve this puzzle, we present a systematic study on the electrical resistivity, ρ(T), which was carried out in ceramic samples of La_0.75Sr_0.20MnO₃ and La_0.75Sr_0.20Mn_1−cCo_cO₃ manganites over the temperature ranges 0.4–60 K and 4–60 K respectively. All compounds show a minimum in the resistivity at a characteristic temperature T_min, which in the Co-doped samples shifts towards higher temperatures as the Co concentration increases. T_min varies approximately as c^1/3. The application of an external magnetic field shows that the T_min decreases linearly as the field increases, and above 0.7 T remains field independent. In magnetic fields, where T_min is constant, T_min varies as . For temperatures below T_min the resistivity data can be fitted either with a or with a −lnT function, while for temperatures above the minimum the resistivity follows both a T³ and a T^5/2 dependence. We believe that there is a crossover between a 'Kondo-like' scattering process and the 3D electron–electron interaction effects enhanced by disorder.

A new tool for analysing theoretically the chemical bonding in solids is proposed. A balanced crystal orbital overlap population (BCOOP) is an energy resolved quantity which is positive for bonding states and negative for antibonding states, hence enabling a distinction between bonding and antibonding contributions to the chemical bond. Unlike the conventional crystal orbital overlap population (COOP), BCOOP handles correctly the situation of crystal orbitals being nearly linear dependent, which is often the case in the solid state. Also, BCOOP is much less basis set dependent than COOP. A BCOOP implementation within the full-potential linear muffin tin orbital method is presented and illustrated for Si, TiC and Ru. Thus, BCOOP is compared to the COOP and crystal orbital Hamilton population (COHP) for systems with chemical bonds ranging from metallic to covalent character.

Heat capacity and electrical resistivity investigations are carried out for stoichiometric La_1−xSr_xMnO₃ manganite compounds. The temperature of the peak of the heat capacity c_p associated with ferromagnetic transition is in agreement with the resistivity measurements. The electrical resistivity shows a roughly AT² dependence over a wide temperature range, where the coefficient A decreases as the content of Sr increases. The results show that the Kadowaki–Woods empirical relation is not valid. It is attempted to explain the dependence of A on the x content of Sr within the framework of electron–electron Umklapp scattering.

We have examined the low temperature magnetic properties of the geometrically frustrated antiferromagnetic pyrochlores Gd₂Sn₂O₇ and Gd₂Ti₂O₇ using specific heat, ¹⁵⁵Gd Mössbauer, magnetic susceptibility and magnetization measurements. For Gd₂Sn₂O₇, the specific heat evidences a single, strongly first order magnetic transition near 1.0 K; in Gd₂Ti₂O₇, we confirm the presence of both the transition near 1.0 K and the second transition near 0.75 K. Below 1 K, magnetic irreversibilities are present in both compounds, but their signature (the difference between the FC and ZFC branches) is more marked in Gd₂Sn₂O₇. At 0.03 K in each compound, the Mössbauer data show that the four Gd³⁺ of a tetrahedron carry moments of equal sizes and on a frequency scale of 120 × 10⁶ s⁻¹ each is oriented perpendicular to the local direction. In Gd₂Ti₂O₇, the Mössbauer data also indicates that the transition at 0.75 K involves a small change in the magnetic structure.

A spectroscopic study of Y b³⁺ ions in Y Al₃(BO₃)₄ laser crystals is presented. Polarized absorption and site selective spectroscopy experiments at low temperature have been used to determine the presence of two different Y b³⁺ centres in this host crystal in the concentration range 0.2–9 at.%. The contribution of these centres to the absorption spectra has been found to be dependent on the total Y b³⁺ concentration, and the Stark energy level diagrams corresponding to the different Y b³⁺ centres have been determined. The importance of electron–phonon coupling in the optical transitions of Y b³⁺ ions has been also pointed out.

Two alternative geometries are proposed for x-ray magneto-optical (MO) spectroscopy with linearly polarized light in photon-in/photon-out reflection experiments, without sophisticated polarization analysis of the reflected x-ray radiation. One of the geometries yields an MO effect that is odd in the magnetization M, i.e., to first order linear in . The other geometry yields a magneto-x-ray effect that is even in M, i.e., to lowest order proportional to . This second MO effect is a promising tool for the x-ray reflection spectroscopy of antiferromagnets. The applicability of these spectroscopies is demonstrated by experimental results.

Cerium doped lutetium pyrosilicate Lu₂Si₂O₇:Ce³⁺ (LPS) single crystals, prepared by the floating zone technique, present good scintillation properties, with a light yield between 15 000 and 31 000 photons MeV⁻¹. However, some LPS crystals prepared by the Czochralski process exhibited quite a low scintillation light output, below 2000 photons MeV⁻¹. Electron paramagnetic resonance experiments show that this scintillation quenching is due to iridium impurities (Ir³⁺) originating from the iridium crucible.