Table of contents

We present the first findings of the spin transistor effect in a Rashba gate-controlled ring embedded in a p-type self-assembled silicon quantum well that is prepared on an n-type Si(100) surface. The coherence and phase sensitivity of the spin-dependent transport of holes are studied by varying the values of the external magnetic field and the bias voltage that are applied perpendicularly to the plane of the double-slit ring. First, the amplitude and phase sensitivity of the 0.7 × (2e²/h) feature of the hole quantum conductance staircase revealed by the quantum point contact inserted in one of the arms of the double-slit ring are found to result from the interplay of the spontaneous spin polarization and the Rashba spin–orbit interaction. Second, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted are shown to define the amplitude and the phase of the Aharonov–Bohm and the Aharonov–Casher conductance oscillations.

Germanium dioxide (GeO₂) is a chemical analogue of SiO₂. Furthermore, it is also to some extent a structural analogue, as the low- and high-pressure short-range order (tetrahedral and octahedral) is the same. However, a number of differences exist. For example, the GeO₂ phase diagram exhibits a smaller number of polymorphs, and all three GeO₂ phases (crystalline, glass, liquid) have an increased sensitivity to pressure, undergoing pressure-induced changes at much lower pressures than their equivalent SiO₂ analogues. In addition, differences exist in GeO₂ glass in the medium-range order, resulting in the glass transition temperature of germania being much lower than for silica. This review highlights the structure of amorphous GeO₂ by different experimental (e.g., Raman and NMR spectroscopy, neutron and x-ray diffraction) and theoretical methods (e.g., classical molecular dynamics, ab initio calculations). It also addresses the structures of liquid and crystalline GeO₂, that have received much less attention. Furthermore, we compare and contrast the structures of GeO₂ and SiO₂, as well as along the GeO₂–SiO₂ join. It is probably a very timely review, as interest in this compound, that can be investigated in the liquid state at relatively low temperatures and pressures, continues to increase.

Elastic forces and structural phase transitions control the architecture and function of bio-membranes from the molecular to the microscopic scale of organization. The multi-component lipid bilayer matrix behaves as a pseudo-ternary system. Together with elastically and electrostatically mediated specific lipid–protein interaction mechanisms, fluid–fluid phase separation can occur at physiological temperatures. This can drive the transient generation of micro-domains of distinct composition within multi-component lipid–protein alloys, enabling cells to optimize the efficiency of biochemical reactions by facilitating or inhibiting the access of enzymes by distinct substrates or regulatory proteins.

Together with global shape changes governed by the principle of minimum bending energy and induced curvature by macromolecular adsorption, phase separation processes can also play a key role for the sorting of lipids and proteins between intracellular compartments during the vesicle mediated intracellular material transport.

Cell adhesion is another example of mechanical force controlled membrane processes. By interplay of attractive lock and key forces, long range disjoining pressures mediated by repeller molecules or membrane undulations and elastic interfacial forces, adhesion induced domain formation can play a dual role for the immunological stimulation of lymphocytes and for the rapid control of the adhesion strength.

The present picture of the thermo-elastic control of membrane processes based on concepts of local thermal equilibrium is still rudimentary and has to be extended in the future to account for the intrinsic non-equilibrium situation associated with the constant restructuring of the cellular compartments on a timescale of minutes.

We review the role of strong electronic correlations in quasi-two-dimensional organic charge transfer salts such as (BEDT-TTF)₂X, (BETS)₂Y, and β'-[Pd(dmit)₂]₂Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerized and is described by a half-filled Hubbard model; the second class is not strongly dimerized and is described by a quarter-filled extended Hubbard model. We argue that these models capture the essential physics of these materials. We explore the phase diagram of the half-filled quasi-two-dimensional organic charge transfer salts, focusing on the metallic and superconducting phases. We review work showing that the metallic phase, which has both Fermi liquid and 'bad metal' regimes, is described both quantitatively and qualitatively by dynamical mean field theory (DMFT). The phenomenology of the superconducting state is still a matter of contention. We critically review the experimental situation, focusing on the key experimental results that may distinguish between rival theories of superconductivity, particularly probes of the pairing symmetry and measurements of the superfluid stiffness. We then discuss some strongly correlated theories of superconductivity, in particular the resonating valence bond (RVB) theory of superconductivity. We conclude by discussing some of the major challenges currently facing the field. These include parameterizing minimal models, the evidence for a pseudogap from nuclear magnetic resonance (NMR) experiments, superconductors with low critical temperatures and extremely small superfluid stiffnesses, the possible spin-liquid states in κ-(ET)₂Cu₂(CN)₃ and β'-[Pd(dmit)₂]₂Z, and the need for high quality large single crystals.

The rotational dynamics of aqueous colloidal dispersions of magnetic nanoparticles is examined whilst increasing the volume fraction up to the formation of a macroscopic solid. The freezing of the rotation is studied by magneto-optical relaxation experiments and related to small-angle neutron-scattering results showing that the structure, albeit imposed by the Coulombic repulsion, remains amorphous because of the size polydispersity. The volume fraction at which the freezing occurs is noticeably dependent on the salinity of the suspension. The latter point is discussed together with the microscopic mechanism of the arrest.

The mean-field analysis of the filling transition is based on the simple effective Hamiltonian. It is valid only in the long-wavelength limit and the transition occurs in the temperature regime where the behaviour of the interface is dominated by fluctuations. We evaluate the correlation function and the roughness of the interface in the Ornstein–Zernike approximation. With the help of the Ginzburg criterion we prove that the mean-field filling transition breaks down in this temperature range. We propose the replacement of the simple effective Hamiltonian with a more complex Hamiltonian evaluated using Landau theory. This Hamiltonian can be used in the temperature regime where fluctuations are negligible and the mean-field analysis is correct.

The equilibrated grain boundary groove shapes for the Cd solid solution in equilibrium with the Cd–Zn liquid have been observed by rapid quenching. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient and the solid–liquid surface energy for the Cd solid solution in equilibrium with the Cd–Zn eutectic liquid have been determined to be (8.16 ± 0.65) × 10⁻⁸ K m and (121 ± 16) mJ m⁻² with the numerical method and from the Gibbs–Thomson equation, respectively. The grain boundary energy for the same material has been calculated as (241 ± 30) mJ m⁻² from the observed grain boundary groove shapes. The thermal conductivities of the solid and liquid phases for Cd–26.5% Zn and Cd–5% Zn alloys have also been measured.

The mechanical unfolding of two proteins belonging to the immunoglobulin superfamily, fibronectin (an extracellular matrix protein) and contactin (a neuronal adhesion protein), was studied by means of atomic force microscopy (AFM). The mean unfolding forces and characteristic lengths describing unfolding events of two types of the immunoglobulin module observed for contactin were compared with results obtained for fibronectin. The results showed that the FnIII-type domain present in both proteins, i.e. in contactin and fibronectin, requires a similar force of about 100 pN to be unfolded. However, the IgC2-type domains of contactin, normally remaining intact in view of the intra-domain disulfide bonds, reveal rather lower stability in the presence of the reducing agent. The force needed to unfold a single IgC2 domain was calculated and established to be about 70 pN.

Initially, natural human fibronectin was chosen only as a reference protein for studies of contactin unfolding force values. However, interesting results were obtained and used as a reference in further analysis of the contactin unfolding pathway. Two characteristic length values were obtained for the FnIII domain type of both studied proteins; thus for both domains the ability to unravel in two different pathways was concluded.

The interfacial structure and dynamical processes of a NaCl nanocrystal in liquid water have been studied in detail through classical molecular dynamics simulations. Before dissolution, the radial distribution of water molecules around the nanocrystal exhibits a multi-shell structure at the solid–liquid interface. The thermodynamic properties of the hydrated NaCl nanocrystal were studied by calculating its kinetic energy distribution and vibrational spectrum, which show a good agreement with experiment. The characteristics of NaCl dissolution dynamics, such as ion sequence, dissolved species, dissolution force, and dynamical role of water molecules during the dissolution were further investigated based on the statistical analysis. An ion sequence of Cl⁻, Na⁺, Cl⁻... and intermitted neutral pairs taking place from corner then ledge sites is preferred in NaCl dissolution processes.

The rate of one phonon decaying into three is calculated in the momentum range where one phonon decaying into two is forbidden in liquid ⁴He. Exact and useful approximate expressions for the rate are obtained. Its dependence on all parameters, and the physical reasons for these dependences, are analysed. It is shown that processes where one phonon scatters into three, and three phonons scatter to one phonon, rapidly establishes equilibrium in anisotropic and isotropic phonon systems. This shows that the momentum range, where one to three phonon processes are allowed, should be included in the subsystem of low-energy phonons where equilibrium occurs quickly, and not in the subsystem of high-energy phonons where spontaneous decay processes are forbidden and equilibrium occurs slowly.

Suspensions of super-paramagnetic colloids trapped in the water–air interface are an excellent model system for the study of two-dimensional systems. Here, we investigate the structural behaviour of two-component mixtures of such particles. The interparticle interactions are tunable through the application of a magnetic field perpendicular to the air–water surface. Further, they can be influenced by the choice of the relative magnetic susceptibilities of the two colloidal species. We have performed integral equation theory and computer simulations to study the static properties of such a binary super-paramagnetic system. For all susceptibility ratios studied, no macroscopic phase separation takes place; the fluid phase remains macroscopically homogeneous but microphase structuring occurs: the interactions with the large particles lead to a clustering of the smaller particles. We combine structural information in reciprocal space together with morphological measures in real space to characterize the ordering of the two species in the binary mixture.

In a previous work, we analysed some regularities found in the behaviour of the thermal expansion coefficient, α_p, in compressed liquids. We confirmed that a given liquid presents a characteristic pressure range in which the condition is fulfilled within a narrow range of reduced densities. We also found that the density at which the condition is satisfied, ρ_α, decreases with temperature, a key feature not described before. Earlier studies by other authors suggested that similar regularities are expected for the reduced bulk modulus, B. We present here a detailed analysis of the temperature and density dependence of B from existing experimental results at high pressures. Several liquids have been analysed: argon, krypton, xenon, ethylene, tetrafluoromethane, trifluoromethane, carbon dioxide, carbon disulfide, n-butane, n-hexane, toluene, ethanol, 1-hexanol, m-cresol, and quinoline. We locate that the density ρ_B that fulfils the condition occurs at a particular region of the phase diagram, between 3.4 and 2.4 times the critical density of each liquid. Interestingly, the previously found density ρ_α is close to ρ_B, in a similar region of the reduced phase diagram. However, we note that ρ_B typically decreases to a lesser extent with temperature than ρ_α. In addition, we have found that ρ_B(T) behaves in a parallel fashion for the different liquids, showing larger values of ρ_B as the complexity of the molecules increases. These findings provide a strong basis for developing general equation of state models to describe the behaviour of liquids in the high-pressure regime.

Based on the method of collective variables, we develop the statistical field theory for the study of a simple charge-asymmetric 1:z primitive model (SPM). It is shown that the well-known approximations for the free energy, in particular the DH limiting law (DHLL) and the optimized random phase approximation (ORPA), can be obtained within the framework of this theory. In order to study the gas–liquid critical point of the SPM we propose a method for the calculation of chemical potential conjugate to the total number density which allows us to take into account the higher-order fluctuation effects. As a result, the gas–liquid phase diagrams are calculated for z = 2–4. The results demonstrate a qualitative agreement with Monte Carlo (MC) simulation data: the critical temperature decreases when z increases and the critical density increases rapidly with z.

Study of the ordered oxygen deficient perovskite EuBaCo_2−xNi_xO_5.50 shows that the doping of cobalt sites by nickel induces a strong ferromagnetic component at low temperature in the antiferromagnetic matrix of EuBaCo₂O_5.50. This system indeed exhibits phase separation, i.e. it consists of ferromagnetic domains embedded in the antiferromagnetic matrix of EuBaCo₂O_5.50. Besides, a magnetic transition is observed for the first time at 40 K in the undoped and nickel-doped phases, which can be attributed to the ferromagnetic ordering of the Eu³⁺ moments below this temperature. Moreover sharp ultra magnetization multisteps are observed below 5 K, characteristic of the motion of domain walls in a 'strong pinning' system and very different from any metamagnetic transition.

The Hartree–Fock random phase approximation (HF-RPA) approach is applied to the one-dimensional (1D) anti-ferromagnetic Heisenberg model in the Jordan–Wigner representation. Somewhat contrary to expectation, this leads to reasonable results for spectral functions and sum rules in the symmetry-unbroken phase. In a preliminary application of self-consistent RPA to finite-size chains, strongly improved results are obtained.

Using an accurate density-functional method, we study a series of ternary transition-metal compounds based on the rock-salt IV–VI semiconductor GeTe for potential use as half-metallic ferromagnets, because some of such materials have already been fabricated and proved experimentally to be ferromagnetic. We find four half-metallic ferromagnets in ternary Cr- and V-substituted compounds and study their electronic structures and charge and spin density to clarify their bonding properties. The half-metallic ferromagnetic order is stable against possible antiferromagnetic orders. The half-metallic ferromagnetism is formed because the exchange splitting of the transition-metal d states is large enough to cause ferromagnetism and keep the minority-spin gap at the Fermi level open. These half-metallic ferromagnets could be useful in spintronics because of their relationship with the semiconductor GeTe.

We investigate non-equilibrium transport properties in a series of quantum dots in which the Kondo resonance is influenced by the coupling between dots. Based on the Anderson Hamiltonian in the strongly interacting limit, we show the splitting of the Kondo resonance at the Fermi surface and the appearance of negative differential conductance when the magnitude of the interdot coupling is in the order of the coupling between the dots and the leads. We illustrate the relationship between the negative differential conductance and the local densities of states at the dots under different biases. We also show the profile of energies of dots in the series when a finite bias is applied. Furthermore, the differences in transport properties between even and odd numbers of quantum dots in the series are investigated.

The effect of thermal annealing on the electrical and structural properties has been studied on a thin film of a-Se₈₅Te₁₅ alloy. The dark (σ_d) and photo-conductivity (σ_ph) increase sharply with the increase in annealing treatment. There is a sharp drop in the photosensitivity (σ_ph/σ_d) of the thin film sample. The dark activation energy (ΔE_d) decreases on thermal annealing treatment. These changes are attributed to the phase transition of the thin film of a-Se₈₅Te₁₅ from amorphous to crystalline phase. This is supported by the x-ray diffraction measurements, which clearly indicate the said phase transition on subjecting the thin film to prolonged thermal annealing treatment.

The temperature dependence of the resistivity, ρ, of ceramic LaMnO_3+δ with δ = 0.065 and 0.154 (or simply # 065 and # 154), is investigated under hydrostatic pressure, p, between the temperatures T = 80 and 320 K in magnetic fields up to 10 T. The data for ρ(T) are analysed within a Shklovskii–Efros-like variable-range hopping conductivity model, governed by a soft Coulomb gap, Δ, and a rigid gap, γ, in the density of localized states. The validity of this approach to the resistivity of LaMnO_3+δ under ambient pressure was established in recent investigations (Laiho et al 2005 J. Phys: Condens. Matter17, 105). In the present work it is shown that upon increasing p up to 11 kbar (# 154) and 13 kbar (# 065) the magnetic Curie temperature, T_C, is increased by ∼12–13%. Correspondingly, Δ(p) is decreased by ∼7–8% and γ(p) by ∼8% in # 154 and 12% in # 065. Similarly, the electron localization radius a(p) is increased by ∼4% in # 154 and 8% in # 065, respectively. The influence of pressure on T_C, Δ, γ and a is interpreted by increasing the electron bandwidth and decreasing the polaron potential well, which stimulates the delocalization of electrons when p is increased.

The simplified positron elastic scattering model presented in this paper is a practical method for simulating the positron elastic process. The model yields a simple analytical formula for the random sampling of the angular deflection, which allows fast calculations of the transport of charged particles in matter, and avoids the problem of the infeasibility of detailed simulations when the energy increases up to hundreds of keV. In order to test our modelling, a simple detailed Monte Carlo code has been used to calculate the backscattering probabilities in the keV range. The simulation results and experiments are found to be in very good agreement.