Table of contents

We have carried out a de Haas–van Alphen experiment under pressure on a heavy-fermion superconductor, CeCoIn₅. Large cyclotron masses of 15 m₀ (m₀: the rest mass of an electron) in a nearly cylindrical Fermi surface called α_i (i = 1, 2, 3) and 60 m₀ in a similar cylindrical Fermi surface called β₂ at ambient pressure are found to be strongly reduced to 7 and 40 m₀, respectively, at 3 GPa. Correspondingly, the field-dependent cyclotron mass at ambient pressure becomes almost independent of the field at high pressures. These results indicate that CeCoIn₅, which is in the vicinity of the quantum critical region at ambient pressure, is changed into a usual heavy-fermion state under high pressures of about 3 GPa.

In this paper, we report a very simple approach to transform a thin silica cap layer, formed by thermal oxidation on Si(001) substrates, into SiO₂ nanowires, i.e. treating the silica cap layer with ferrocene molecules, heating it up in argon flow and then exposing it to methane at ∼1000°C. During the heating process ferrocene molecules reacted with the silica surface through some chemical procedures and formed circular templates on the silica surface from which silica nanowires started to develop when exposed to methane. The nanowires so produced are amorphous, ∼15 nm in diameter and several hundred micrometres in length. Prolonged exposure to methane at this temperature transformed completely the silica cap layer into nanowires. This study provides a new method to fabricate silica nanowires on planar substrates.

Single-molecule fluorescence spectroscopy is emerging as an important tool for studying biomolecular folding dynamics. Its usefulness stems from its ability to directly map heterogeneities in folding pathways and to provide information about the energy landscape of proteins and ribonucleic acid (RNA) molecules. Single-molecule fluorescence techniques relevant for folding studies, including methods for trapping and immobilizing molecules, are described and compared in this review. Some emphasis is placed on fluorescence resonance energy transfer, which is particularly useful for studying conformational dynamics of biomolecules. Studies on protein and RNA folding using this methodology are reviewed and set in the more general context of folding science. Finally, some of the interesting future prospects in this field are delineated.

In this topical review we discuss the nature of the low-temperature phase in both infinite-ranged and short-ranged spin glasses. We analyse the meaning of pure states in spin glasses, and distinguish between physical, or 'observable', states and (probably) unphysical, 'invisible' states. We review replica symmetry breaking (RSB), and describe what it would mean in short-ranged spin glasses. We introduce the notion of thermodynamic chaos, which leads to the metastate construct. We apply these tools to short-ranged spin glasses, and conclude that RSB, in any form, cannot describe the low-temperature spin glass phase in any finite dimension. We then discuss the remaining possible scenarios that could describe the low-temperature phase, and the differences they exhibit in some of their physical properties—in particular, the interfaces that separate them. We also present rigorous results on metastable states and discuss their connection to thermodynamic states. Finally, we discuss some of the differences between the statistical mechanics of homogeneous systems and those with quenched disorder and frustration.

In the past decade, nanometre-scale pores have been explored as the basis for technologies to analyse and sequence single nucleic acid molecules. Most approaches involve using such a pore to localize single macromolecules and interact with them to garner some information on their composition. Though nanopore sensors cannot yet claim success at deoxyribonucleic acid (DNA) sequencing, nanopore-based technologies offer one of the most promising approaches to single molecule detection and analysis. The majority of experimental work with nanopore detection of nucleic acids has involved the α-haemolysin (alpha-HL) ion channel—a heptameric protein with a ∼2 nm diameter inner pore which allows translocation of single-stranded DNA. Analysis of externally induced ion current through the pore during its interaction with DNA can provide information about the DNA molecule, including length and base composition. This review focuses on alpha-HL and its applications to single-molecule detection. Modified alpha-HL and other biological and synthetic pores for macromolecule detection are also discussed, along with a brief summary of relevant theoretical work and numerical modelling of polymer–pore interaction.

Using reverse non-equilibrium molecular dynamics simulations, we report the calculation of the shear viscosity and the tracer diffusion coefficient of a binary Lennard-Jones mixture that is known as a model glass-former. Several remarkable temperatures are well reproduced in our calculations, i.e. T_S (the onset of slow dynamics), T_c (the critical temperature predicted by the mode-coupling theory) and T_K (the Kauzmann temperature). A breakdown of the Stokes–Einstein relation is found at temperature T_S. We propose that, at low temperatures below T_S, the size of single-particle positional fluctuations between particle-hopping events corresponds to the length measured by the Stokes–Einstein relation, which is equated to the hydrodynamic radius of particles at high temperatures.

In the original description of fragility, Angell (1988 J. Phys. Chem. Solids49 863) determined the degree of fragility from the curvature on an Arrhenius plot. This paper discusses a new measurement of the fragility value. The fragility of Al–Ni-based glass-forming melts, which is seldom reported in this field, can be analysed by using data from their viscosity and thermal properties. The fragility is observed to be very high, which is in very good agreement with the low glass-forming ability of Al–Ni-based alloys.

The equilibrium sedimentation profiles of polydisperse van der Waals fluids have been calculated within the framework of the density functional theory of non-uniform polydisperse fluids. The main focus is on the delicate balance between the gravitational force, the interparticle attraction, and the excluded volume effects. In the presence of gravity, a polydisperse system will experience size segregation. This trend is reinforced when the polydispersity of the fluid is increased. The details of this size segregation are quite sensitive to how the different parts of the interparticle interactions depend on the polydispersity. In the present work, it is also shown that, within the local density approximation, the density profiles can be inverted to give the osmotic pressure. This suggests a practical way of measuring the equation of state of polydisperse colloidal dispersions.

The dynamics of ethanol in its plastic crystalline and supercooled liquid state has been measured using triplet state solvation dynamics techniques. This study focuses on temperatures near the respective glass transitions T_g of the two distinct phases, where the structural relaxation times are between 1 ms and 10 s. In the plastic crystal, the correlation times of the Stokes shift dynamics match the longitudinal time constants of the system as derived from dielectric relaxation data. Additionally, a maximum of the time resolved optical linewidths is indicative of heterogeneous dynamics in the plastic crystal. The supercooled liquid state is obtained after quenching the liquid from room temperature to below T_g and displays relaxation times that are a factor of 100 faster compared with the plastic crystal at the same temperature. The results do not reveal different translational contributions to solvation for the two phases.

The heat capacity of cyclooctanol was measured with an adiabatic calorimeter in the temperature range 5–340 K. Liquid cyclooctanol crystallized into crystal I, a plastic (orientationally disordered) phase. Crystal I was supercooled readily and underwent a glass transition at 160 K. Crystal II, obtained by annealing crystal I at about 200 K, also underwent a glass transition at 160 K, indicating that crystal II is also an orientationally disordered phase. On heating, crystal II transformed to crystal I at 261.7 K with a transition entropy of 8.06 J K⁻¹ mol⁻¹ and crystal I fused at 295.3 K with a fusion entropy of 7.00 J K⁻¹ mol⁻¹. Neutron scattering of cyclooctanol was measured in the temperature range 20–335 K, energy range 0.1–20 meV and momentum transfer range 0.23–2.7 Å⁻¹. A clear boson peak was found around 2.5 meV in both orientational glasses of crystal I and II. Quasielastic scattering appeared at temperatures as low as the glass transition temperature. This may be due to a fast β process which has been observed in most glass-forming liquids. The present results indicate that glass-forming plastic crystals are similar to glass-forming liquids in their dynamical properties in terahertz region.

We have studied one aspect of the effect of Coulomb interactions on the hopping conductivity of a band of localized electrons in a disordered system, that is correlations in successive hops due to the Coulomb gap. At low temperatures, the correlation holes around sites involved in the hop do not relax, and there is an enhanced probability for backward hops. We calculate both dc and ac conductivities by considering correlated random walks in the disordered medium.

The liquid-crystalline polymer system formed by solutions of hydroxypropylcellulose in water has a well known anomaly in the dependence of its mechanical complex modulus on its rheological history. After cessation of an initial rapid shear, the system evolves towards an 'equilibrium' state with a high modulus; after slow shear the 'equilibrium' state has a low modulus. Attempts to distinguish the two states by light scattering, birefringence or x-ray scattering have been unsuccessful. We present the first locally probing experiment, rheo-NMR, that sees a difference between these states. The results show clearly that the low-modulus state is ordered and evolves out of a state that has no macroscopic order (but may be ordered at the mesoscopic level) immediately after cessation of the shear. The high-modulus state is much less ordered, although it evolves from a rather well flow-aligned state immediately after cessation of the shear.

⁷¹Ga nuclear magnetic resonance studies were carried out for liquid gallium embedded into porous glasses with different pore sizes and into artificial opals within the temperature range from about 320 K to complete confined gallium freezing. A general decrease in the Knight shift compared to the bulk melt depending on pore sizes was observed in contrast to theoretical predictions. Correlations between alterations in the Knight shift and pore sizes were established for particular pore geometry. It was also observed that confined geometry affects the temperature dependence of the Knight shift in liquid gallium.

High-dimensional energy landscapes of complex systems often exhibit a very complicated barrier structure. For the analysis of the dynamics on such landscapes, purely 'energetic' considerations are no longer sufficient, and 'entropic' and/or 'dynamical' contributions must be taken into account. We show how such 'non-energetic' barriers should be treated on a conceptually equal footing with classical 'energetic' barriers, and present a region belonging to a simple model of a crystalline compound, CaF₂, which is stabilized by 'non-energetic' barriers alone.

The spectrum, electron-density distribution and ground-state correlation energy of two electrons confined by an anisotropic harmonic oscillator potential have been studied for different confinement strengths ω by using the quantum chemical configuration interaction (CI) method employing a large Cartesian anisotropic Gaussian basis set and a full CI wavefunction. Energy level diagrams and electron-density distributions are displayed for selected electronic states and confinement parameters. The total energy and spacing between energy levels increase in all cases with increasing ω. The energy level structure cannot be matched by scaling with respect to ω. The correlation energy of the ground state is comparable in magnitude to that of the helium atom. It increases for increasing ω. The percentage of the correlation energy with respect to the total energy of the ground state is considerably larger than that of the helium atom.

Quantum confinement shifts quantum phase transitions like the λ-point of liquid helium. This effect is calculated here for ideal Bose–Einstein condensates (BECs) using thermodynamic mapping (TM). TM is a procedure to obtain low temperature behaviour from high temperature information via elementary transformations. We report here a series of TM relations for thermodynamic quantities and the resulting transition properties for ideal BECs.

Bonding of the bridging oxygen (BO) and non-bridging oxygen (NBO) sites in the CaSiO₃ silicate is studied using soft x-ray emission, absorption and electron energy-loss spectroscopy of the oxygen K edge. Comparisons with APW + lo calculations are discussed, showing that this method can be applied successfully to silicates, which have large unit cells. Several specific features due to BO and NBO atoms in the density of states are reproduced by the calculations. The bonding in CaSiO₃ is also examined using electron density maps. Our analysis of deformation electron density maps supports the idea that the NBO to Si bond is more ionic than the BO to Si bond.

We have prepared samples of nominal type Ba₈Cu_xGe_46−x by induction melting and solid state reaction. Analysis shows that these materials form type-I clathrates, with a copper content between x = 4.9 and 5.3, nearly independent of the starting composition. We used x-ray powder diffraction and single-crystal electron diffraction to confirm the cubic type-I clathrate structure, while electron microprobe measurements confirmed the stability of the x ≈ 5 composition. This result differs from the corresponding Ag and Au clathrates and was not known previously due perhaps to the similar Cu and Ge form factors in x-ray diffraction. The observed composition adheres very tightly to a valence-counting scheme, in agreement with a Zintl-type stability mechanism. This implies a gap in the electronic density of states, also in contrast to the metallic behaviour of the Au and Ag analogues. Magnetization measurements showed a large diamagnetic response in the Ba–Cu–Ge clathrate. This behaviour is consistent with semiconducting or semimetallic behaviour and is similar to that of a number of intermetallic semiconductors.

In the equilibrium immiscible Cu–V system, interesting structural evolution was observed in the Cu–V multilayers upon 200 keV xenon ion beam mixing at 77 K. In the Cu₃₀V₇₀ sample, a unique amorphous phase was formed. In the Cu₇₄V₂₆ sample, an amorphous phase was partially formed and it transformed, after an over-irradiation dose, into a mixture of fcc and bcc solid solutions. The lattice constants of the fcc and bcc solid solutions were determined to be much larger than those of Cu and V, respectively, and can probably be attributed to a strong repulsive interaction between the Cu and V atoms. The observed structural evolution was discussed in terms of a thermodynamic calculation based on Miedema's theory and in terms of atomic collision triggered by ion irradiation.

The thermal expansion and specific heat measurements under ambient pressure and the thermomagnetization measurement under applied pressure for new Lu₆(Mn_1−xFe_x)₂₃ compounds have been carried out in order to discuss the relationship between the thermal expansion anomaly and the spin fluctuations. The thermal expansion coefficient α significantly increases above the Curie temperature T_C. The electronic specific heat coefficient increases with increasing x, accompanied by the decrease of the spin fluctuation spectral width. The value of the pressure dependence of T_C, ∂T_C/∂P, is large at about −50 K GPa⁻¹. The anti-invar effect and the pressure effect of T_C are closely related to a significant thermal variation of the amplitude of spin fluctuations.

We perform a many-body investigation of the spin dephasing in n-type InAs quantum wells under moderate magnetic fields in the Voigt configuration by constructing and solving numerically the kinetic Bloch equations. We obtain the spin dephasing time due to the Rashba effect together with the spin-conserving scattering such as electron–phonon, electron–nonmagnetic impurity as well as electron–electron Coulomb scattering. By varying the initial spin polarization, temperature, impurity density, applied magnetic field and the interface electric field, we are able to study the spin dephasing time under various conditions. For the electron density and quantum well width that we study, the many-body effect dominates the spin dephasing. Moreover, we find an anomalous resonance peak in the spin dephasing time for high initial spin polarization under moderate magnetic fields.

The influence of bias illumination level and carrier diffusion on the modulated photocurrents (MPCs), measured in amorphous solids in a sandwich electrode configuration, is investigated theoretically. Based on the multiple-trapping model the approximate formulae for MPCs, taking into account the mentioned physical factors, are derived. It is demonstrated that the absolute magnitude of the density of states can be determined from the MPC frequency spectra, measured at suitable bias illumination intensities. The carrier diffusion affects the MPCs solely for relatively high modulation frequencies and/or low applied voltages. The criterion for neglecting the diffusion effect is given. The corresponding frequency dependences of the photocurrent phase shift and amplitude as well as of the related quantities, calculated for the exponential trap distribution, are presented.

We propose toy models of crossed Andreev reflection in multiterminal hybrid structures containing out-of-equilibrium conductors. We apply the description to two possible experiments: (i) to a device containing a large quantum dot inserted in a crossed Andreev reflection circuit, and (ii) to a device containing an Aharonov–Bohm loop inserted in a crossed Andreev reflection circuit.

The mixing effects of light and heavy rare earths in cubic Laves phase compounds Nd_1−xHR_xCo₂ (HR = Gd,Tb) have been investigated by means of x-ray powder diffraction and magnetic measurements. In Nd_1−xTb_xCo₂, the saturation moment M_S exhibits an anomaly and could be ascribed to an abrupt jump of the Co moment at a critical concentration x_c ≈ 0.33, whereas, in Nd_1−xGd_xCo₂, M_S does not show such an anomaly and a relatively simple magnetic behaviour is observed at x_c ≈ 0.43. The different behaviours of these two systems can be understood by considering the structural distortion of a cubic unit cell at low temperature. A field-induced metamagnetic transition from weak ferrimagnetism to strong ferrimagnetism is observed in both systems. This can be interpreted by the evolution of magnetization with the help of percolation theory. The compensation points are observed in both systems, which are well explained within the two-sublattice model. A double peak of the AC susceptibility observed in Nd_1−xTb_xCo₂ near x₀ ≈ 0.19 does not necessarily mean the occurrence of a first-order phase transition. The observed second-order magnetic phase transition near x₀ can be well described by Landau theory of the phase transition.

The structure and magnetic properties of high-energy-milled R₄₀Fe₃₀Co₁₅Al₁₀B₅ (R = Nd, Pr) have compounds been investigated by means of x-ray diffraction, high-resolution transmission electron microscopy, magnetic measurements, and Mössbauer spectroscopy. The x-ray diffractograms of the as-milled alloys are typical for the amorphous state. Nanocrystalline R₂(Fe,Co,Al)₁₄B coexisting with R₆(Fe,Co)_13−xAl_1+x is observed after recrystallization at 750°C. The mechanically milled amorphous samples exhibit a relatively moderate coercivity of ≈6.5 kOe at room temperature and a Curie temperature (T_C) ≈ 650 K. After subsequent annealing, both systems show hard magnetic behaviours—such as a record-high coercivity of 29 kOe with approximately the same T_C as for amorphous as-milled alloys.

We have investigated the structural stability and magnetic properties of SmCo_7−xCu_x compounds with the TbCu₇-type structure using x-ray powder diffraction and magnetic measurement. A large solid solution with 0.8 ≤ x ≤ 4.0 in SmCo_7−xCu_x compounds has been observed. Both the lattice parameters and unit cell volume increase with increasing Cu content. SmCo_7−xCu_x compounds exhibit ferromagnetic order. A strong uniaxial magnetocrystalline anisotropy with an anisotropy field as high as 20 T is obtained with x = 0.8 at 5 K. However, the saturation magnetization and Curie temperature decrease with increasing Cu content.

Magnetic properties of copper chloride hydroxide were studied by using a superconducting quantum interference device. The coercivity of this material was more than 10 000 Oe at 2 K, which is the highest observed in the copper compounds. The magnetic susceptibility as a function of temperature revealed ferrimagnetism in the sample.

The evolution of hyperfine interactions with temperature is studied for Fe₈₀M₇Cu₁B₁₂ (M = Mo, Nb and Ti) nanocrystalline alloys with the help of ⁵⁷Fe Mössbauer spectrometry. The nanocrystalline structure features an amorphous residual matrix surrounding the crystalline nanograins of bcc-Fe. In addition, interfacial regions comprising atoms located on the surface of nanocrystals are considered. Special attention is paid to the temperature behaviour of hyperfine magnetic fields of the nanograins. The temperature dependence of hyperfine magnetic fields pointed out significant differences between bulk and nanosized bcc-Fe, suggesting a decrease in the corresponding magnetic ordering temperature. The higher the crystalline content is, the lower the difference between the hyperfine fields of bulk bcc-Fe and nanocrystalline Fe grains. This tendency is observed for M = Nb and Ti whereas it is completely opposite for M = Mo. The present results are explained in terms of mechanical stresses induced during the transformation from the amorphous to the nanocrystalline state, thus excluding a significant number of impurities diffused into the nanocrystalline grains.

An analytical bond-order potential for GaN is presented that describes a wide range of structural properties of GaN as well as bonding and structure of the pure constituents. For the systematic fit of the potential parameters reference data are taken from total-energy calculations within the density functional theory if not available from experiments. Although long-range interactions are not explicitly included in the potential, the present model provides a good fit to different structural geometries including defects and high-pressure phases of GaN.