We have studied the torque signal due to flux lines initially starting from the in-plane, equilibrium configuration, when the magnetic field is tilted away from this direction, for a (${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${)}_2$${\mathrm{CuO}}_4$ single crystal (x=0.075) with a small transverse demagnetizing factor. The deviation of the signal from the one arising from a locked configuration of flux lines is used to detect unlocked configurations. The component of the field perpendicular to the plane direction at which unlocked configurations are manifest is independent of the parallel component, smaller than the first critical field in this direction, and goes to zero well below ${\mathit{T}}_{\mathit{c}}$, in agreement with the theoretical predictions for a layered superconductor with moderate anisotropy. We cannot rule out, however, an overestimation of the transverse critical field for lock-in from our data, due to pinning.

We report absolute reflectivity measurements on ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_3$ in both normal and superconducting states. The superconducting-gap value was determined to be 2Δ=90±10 ${\mathrm{cm}}^{\mathrm{-}1}$, which gives 2Δ/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$=4.2±0.5, consistent with previous experiments. However, finite absorption below 2Δ frequency was found. No Holstein shift of the phonon-related spectrum was observed. Optical conductivity below 2 eV consists of two contributions: a narrow (≤350 ${\mathrm{cm}}^{\mathrm{-}1}$) Drude-like part (Drude component) and an overdamped midinfrared component. We suggest that while the carriers responsible for the Drude contribution form the superfluid at T<${\mathit{T}}_{\mathit{c}}$, the carriers responsible for the midinfrared one remain normal and account for the finite absorption inside the superconducting gap. The value of the London penetration depth ${\lambda }_{\mathit{L}}$ was determined to be (4550±300) Å. Anomalous temperature dependence of reflectivity at temperatures above ∼120–150 K was observed.

${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Eu}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ powder samples, with x=0, 0.25, 0.5, 0.75, and 1.0, were synthesized at ambient pressure using either an acetate-tartrate sol-gel method or a LiF flux process. The lattice parameters and purity of the samples were checked using X-ray diffraction. The superconducting transition was monitored by magnetic-susceptibility measurements. Replacing yttrium with europium increased the unit-cell volume, decreased the orthorhombicity (b/a) and the critical temperature. The hyperfine interactions at the europium site were studied by ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ Mössbauer spectroscopy. The complete quadrupole Hamiltonian of the 21.5-keV γ transition of ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ was successfully applied in the analyses of the Mössbauer spectra. The Mössbauer parameters obtained were found to resemble those measured for the ${\mathrm{EuBa}}_2$${\mathrm{Cu}}_3$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (1:2:3) system. It was demonstrated that magnetic alignment of the crystallites could not be obtained with an 11.7-T field, contrary to the 1:2:3 and other high-${\mathit{T}}_{\mathit{c}}$ systems. The magnetic susceptibility for 1:2:4 single crystals appears to be isotropic.

Superconducting properties of coupled Hubbard planes are studied by quantum Monte Carlo simulations. It is found that the interlayer coupling supports the pairing mechanism but it does not lead to off-diagonal long-range order in the purely electronic system. In addition, we have performed Monte Carlo studies based on a recently proposed variational wave function. Yielding identical results, the variational wave function overcomes the sign problem and allows us to analyze ground-state properties of strongly correlated many-body problems for system sizes and complexities not accessible otherwise.

The properties of the structural twins in R${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ compounds are investigated in a wide range of temperatures in the framework of the suggested model. The dependence of the size of the twins versus temperature is considered. The temperature interval of the sharp increase of twin size with increase of the temperature is found.

Samples of ${\mathrm{La}}_2$${\mathrm{CuO}}_{4+\mathrm{\delta }}$ in the range 0<δ<0.1 were prepared by electrochemical insertion of oxygen in KOH; the oxygen content was determined by iodometric titration. The temperature variations of resistance R and Seeback coefficient α were used to monitor as a function of the compositional parameter δ not only the evolution of the superconductive transition temperature ${\mathit{T}}_{\mathit{c}}$, but also the diffusion-controlled spinodal phase segregation occurring in the temperature range 200<T≤300 K. The data also show that the δ interstitial oxygen atoms ${\mathrm{O}}_{\mathit{i}}$ per formula unit enter as ${\mathrm{O}}_{\mathit{i}}^{2\mathrm{-}}$ ions at least in the range 0<δ≤0.070. Comparison of the transport properties of samples slow-cooled from room temperature to 77 K reveals an ${\mathrm{O}}_{\mathit{i}}$-atom segregation over the range 0<δ≤0.066; this segregation disappears for δ>${\mathrm{\delta }}_{\mathit{o}}$ where the ${\mathrm{O}}_{\mathit{i}}$ atoms become ordered, and 0.066<${\mathrm{\delta }}_{\mathit{o}}$<0.070 was determined. Analysis of neutron-diffraction data from available literature gives a spinodal decomposition temperature ${\mathit{T}}_{\mathit{s}}$ vs δ that falls to 200 K at ${\mathrm{\delta }}_{\mathit{s}}$(max)≊0.05; the diffusion-controlled spinodal phase segregation occurs within the phase field of the ${\mathrm{O}}_{\mathit{i}}$-disordered orthorhombic structure.

The oxygen-rich phase having ${\mathrm{\delta }}_{\mathit{s}}$(max)≊0.05 is superconductive with a zero-resistance temperature ${\mathit{T}}_0$=26 K that is lower than the ${\mathit{T}}_0$=32 K observed for δ>${\mathrm{\delta }}_{\mathit{o}}$; ${\mathit{T}}_0$ falls to a minimum near δ=0.0625 within the compositional range ${\mathrm{\delta }}_{\mathit{s}}$(max)<δ<${\mathrm{\delta }}_{\mathit{o}}$, which suggests the presence of a competitive nonsuperconductive line phase near p=1/8 holes per Cu atom as is found in the ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_4$ system near x=1/8. A nonsuperconductive transition at ${\mathit{T}}_{\mathit{d}}$=47±1 K was found in slow-cooled samples over the range 0<δ<${\mathrm{\delta }}_{\mathit{o}}$; it is suppressed by both high pressure and the quenching procedure. We associate it with the competitive nonsuperconductive phase stabilized near p=1/8. In the ordered-${\mathrm{O}}_{\mathit{i}}$ phase found for δ>${\mathrm{\delta }}_{\mathit{o}}$, a ‘‘tail’’ in the R-vs-T curve extends into the superconductive temperature range where α=0; it is attributed to a liquid-vortex state rather than a second superconductive phase. The pressure dependences of ${\mathit{T}}_{\mathit{c}}$ and the ${\mathrm{O}}_{\mathit{i}}$-atom mobility were used to distinguish the superconductive phases found for δ<${\mathrm{\delta }}_{\mathit{o}}$ and δ>${\mathrm{\delta }}_{\mathit{o}}$. The appearance of a nonsuperconductive line phase in the interval ${\mathrm{\delta }}_{\mathit{s}}$(max)<δ<${\mathrm{\delta }}_0$ permits reconciliation of the data, including indirect evidence for charge fluctuations stabilized below a ${\mathit{T}}_{\mathrm{\rho }}$<150 K in this interval. The indirect evidence for charge fluctuations is the same as that discussed by us elsewhere in the framework of a model developed for the system ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$.

Magnetic- and electric-field effects on the width, surface tension, and velocity of the interphase boundary are calculated for solid-solid and nematic-isotropic first-order phase transitions described by the Landau expansion with a cubic term. The exact solution of the Ginzburg–Landau–de Gennes equation including an external field is obtained. The results are compared with the experimental data in nematic liquid crystals and ferroelectrics.

We show that Cu ions doped in (${\mathrm{K}}_{\mathit{x}}$${\mathrm{Na}}_{1\mathrm{-}\mathit{x}}$${)}_{0.4}$(${\mathrm{Sr}}_{\mathit{y}}$${\mathrm{Ba}}_{1\mathrm{-}\mathit{y}}$${)}_{0.8}$${\mathrm{Nb}}_2$${\mathrm{O}}_6$ (KNSBN) form two energy levels in the band gap, which increase the effective charge-combination-center concentration ${\mathit{N}}_{\mathrm{eff}}$. The two-wave coupling gain and the response speed of KNSBN crystals are increased while the photoconductivity and the effects of a dc field on the photorefractive properties are reduced. Self-pumped phase conjugation (SPPC) experiments have revealed that the effects of Cu ions on the photorefractive properties have a wavelength dependence. The SPPC response time at the ${\mathit{e}}^{\mathrm{-}1}$ level can be shortened to 200 ms.

We present an analytical study of a nonlinear diatomic chain with cubic and quartic interaction potential between first and second neighbors. In the semidiscrete approximation, using a decoupling ansatz for the motion of the two different sublattices, we obtain oscillating soliton solutions of the asymmetric envelope or dark type.

Measurements of the low-temperature spontaneous resistive anisotropy (SRA) in ternary (${\mathrm{Pd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${)}_{95}$${\mathrm{Mn}}_5$ are presented; the SRA are shown to be consistent with a power-law behavior for this parameter, viz. SRA∝(c-${\mathit{c}}_0$)/${\mathit{c}}_0$, and the exponent associated with the power law is estimated.

In a search for high-magnetostrictive materials we have discovered in FeRh a large induced volume magnetostriction (≊0.82%) at and above room temperature. Thermal-expansion measurements performed on the ordered CsCl crystallographic structure of FeRh in the temperature range 250–800 K reveal Invar-like behavior at ${\mathit{T}}_{\mathit{c}}$=680 K associated with a paramagnetic-ferromagnetic second-order phase transition. At ${\mathit{T}}_{\mathrm{F}\mathrm{-}\mathrm{AF}}$=405 K, a large contraction of the lattice within the ferromagnetic (F) phase takes place through a first-order transformation resulting in a low-volume, low-temperature antiferromagnetic phase (AF) (anti-invar-like behavior). At moderate fields above room temperature and within the AF phase, we have found a giant value for the volume magnetostriction of ω=8.2×${10}^{\mathrm{-}3}$. These results constitute evidence for the existence of the theoretically predicted metastable F phase (high-volume state) within the AF phase which can be reached by an applied magnetic field. The present experiments offer additional perspectives on an old problem in magnetism and suggest potential applications of this alloy as a high-magnetostrictive material.

We present first-principles calculations of the magnetization density and its resolution into spin and orbital moments in ${\mathrm{CeFe}}_2$. The calculations do not rely on any shape assumptions concerning the density or potential and verify that the total moment on the Ce and Fe sites are coupled antiparallel. This is due to the fact that the Fe and Ce spin moments are coupled antiparallel and that the orbital moment on the Ce site is smaller than the spin moment. We argue that this is in sharp contrast to the expected behavior for a 4f local moment system, where essentially the free-ion behavior of the Ce magnetism is expected, with an orbital moment larger and antiparallel to the spin moment. The recent suggestion of a large nonspherical moment density in ${\mathrm{CeFe}}_2$ is specifically addressed and the calculations are found to support such a behavior. The calculated individual moments are ∼50% larger than the moments deduced from neutron-scattering experiments.

The experimental setup for contactless conductivity measurements is reported which can easily be operated at frequencies ${10}^6$≤ν≤${10}^9$ Hz. The technique is applied to complex conductivity measurements in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ at temperatures from 4 to 300 K. The results are compared with data obtained by conventional techniques.

de Haas–van Alphen (dHvA) oscillations corresponding to five extremal areas of the Fermi surface have been observed in the vortex state of ${\mathrm{Nb}}_3$Sn, in magnetic fields as low as ∼0.5${\mathit{B}}_{\mathit{c}2}$. Both the dHvA frequencies and effective masses are unchanged from their values in the normal state, although the quantum oscillations experience a field-dependent additional damping in the superconducting state. The results show that the Landau quantization of quasiparticles persists in the mixed state of a clean type-II superconductor.

The lower critical fields of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.95}$ have been determined by magnetization M(H) measurements using an ellipsoidal-shaped crystal and a thin platelet for H∥c and H⊥c, respectively. Careful data analysis rules out the effects of surface barriers. The data show a linear temperature dependence of ${\mathit{H}}_{\mathit{c}1}$ below about 0.5${\mathit{T}}_{\mathit{c}}$, with ${\mathit{H}}_{\mathit{c}1}$(0)=1100 Oe and 200 Oe for H∥c and H⊥c, respectively. The anisotropy factor γ is almost temperature independent and has the value 5.6±0.3. By comparison of the ${\mathit{H}}_{\mathit{c}1}$ data to results of London penetration-depth measurements, the vortex core energy is found to be linear with temperature.

We present heat-capacity measurements in a magnetic field up to 7.7 T on the recently discovered borocarbide intermetallic superconductors ${\mathrm{LuNi}}_2$${\mathrm{B}}_2$C and ${\mathrm{LaPt}}_{1.7}$${\mathrm{Au}}_{0.3}$${\mathrm{B}}_2$C. For ${\mathrm{LuNi}}_2$${\mathrm{B}}_2$C with ${\mathit{T}}_{\mathit{c}}$=16.5 K, we find a large density of states at the Fermi level, γ∼19(2) mJ/mole ${\mathrm{K}}^2$, and an effective Debye temperature ${\mathrm{\Theta }}_{\mathit{D}}$ of 345 K. In comparison, ${\mathrm{LaPt}}_{1.7}$${\mathrm{Au}}_{0.3}$${\mathrm{B}}_2$C, with ${\mathit{T}}_{\mathit{c}}$=10.2 K, has a γ of 7.5(1.5) mJ/mole ${\mathrm{K}}^2$ and a smaller Debye temperature ${\mathrm{\Theta }}_{\mathit{D}}$ of 220 K. Through comparison with the specific-heat anomaly at ${\mathit{T}}_{\mathit{c}}$, ΔC/γ${\mathit{T}}_{\mathit{c}}$, the magnetic susceptibility, and the calculated band structure, these compounds are found to be in the weak-to-intermediate coupling limit with λ≊0.5–1.0. Their position on the γ-${\mathit{T}}_{\mathit{c}}$ plot indicates dominant phonon-mediated electron pairing.

The dispersion relation of photons transmitting through a photonic one-dimensional quasicrystal arranged in a Fibonacci sequence was observed by measuring the spectrum of the phase change of the transmitted light using a Michelson-type interferometer. The phase spectrum obtained clearly showed the self-similar structure characteristic to dispersion curves of Fibonacci lattices.

The distribution of nonequivalent aluminum sites was studied in Al-Cu-Fe and Al-Cu-Ru stable icosahedral quasicrystalline phases using ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ NQR spectra taken at 4.2 K. The observed spectra—which give directly the distribution of nonequivalent aluminum sites—were broad, asymmetric, and structureless. A simple electric-field-gradient model calculation accounted for the spectral width in terms of a wide distribution of local atomic environments, and an estimate for the lower limit on the number of nonequivalent aluminum sites was found.

We propose a mean-field lattice rate model for describing the kinetics of equilibrium as well as irradiation-induced surface segregation in concentrated alloys. The kinetics and thermodynamics are treated in a mutually consistent way. The model treats the composition field of the chemical constituents and of the point defects. The latter are nonconservative and are produced and destroyed either by the nuclear collisions in the bulk or by thermally activated exchange of the atoms with the free surface. The few adjustable parameters can be scaled to the thermodynamics and kinetics of the alloy. Published experimental segregation profiles in Ni-Cu alloy with two compositions and three temperatures are successfully reproduced with a single set of parameters: they exhibit inversion of segregation induced by irradiation.

The effect of grain size on the magnetoresistance (MR) of Co/Cu multilayers fabricated by dc magnetron sputtering has been studied using Co/Cu multilayers grown with identical Co and Cu thicknesses but different grain sizes. These multilayers were selectively fabricated by growing with and without a Cu underlayer: grain-to-grain epitaxy from the buffer layer to the superlattice in the former facilitated control of the multilayer grain structure. The MR was found to increase with increasing grain size, with the difference being larger at low temperature. The enhancement of MR is attributed to an increased electron mean free path leading to sampling of more antiferromagnetically coupled layers.