Magnetic properties of infinitely long and wide slablike Josephson-junction arrays (JJA’s) consisting of 2N+1 rows of grains are calculated for the dc Josephson effect with gauge-invariant phase differences. When N is large, the intergranular magnetization curve, ${\mathit{M}}_{\mathit{J}}$(H), of the JJA’s in low fields approaches that of uniform Josephson junctions with lengths equal to the thicknesses of the JJA’s, but in a larger field interval, its amplitude is dually modulated with periods determined by the junction and void areas. ${\mathit{M}}_{\mathit{J}}$(H) curves for small N are more complicated. The concept of Josephson vortices and the application of the results to high-${\mathit{T}}_{\mathit{c}}$ superconductors are discussed.

The suppression of ${\mathit{T}}_{\mathit{c}}$ by pairs of dopants which substitute for Cu in superconducting ${\mathrm{YBa}}_2$[${\mathrm{Cu}}_{0.95}$(${\mathit{M}}_{\mathit{x}}$${\mathit{N}}_{1\mathrm{-}\mathit{x}}$${)}_{0.05}$${]}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (${\mathit{M}}_{\mathit{x}}$${\mathit{N}}_{1\mathrm{-}\mathit{x}}$= ${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$,${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{Zn}}_{1\mathrm{-}\mathit{x},}$${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$, ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$) is found to be nonlinear in the concentration x when the dopants occupy both of the inequivalent Cu sites, indicating a strong interlayer coupling. The response is distinctly different for magnetic and nonmagnetic ions. The large suppression due to Zn ions is shown to be correlated with a similar increase in hole density, which is relevant for comparing current theories of s-wave and d-wave superconductivity.

Anisotropic London theory is used to predict the Abrikosov flux lattice for arbitrary field orientations in crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ by minimizing the Gibbs free energy for samples of a planar geometry. At low fields the vortex-chain state exists, i.e., the interchain vortex separation scales as the inverse flux density 1/B whereas the intrachain vortex seperation is constant. At higher fields there is a crossover to the uniaxially distorted hexagonal lattice where the intervortex separation scales as 1/${\mathit{B}}^{1/2}$. At low fields the vortex lattice is inclined towards the c^ axis, rotating towards the applied field at higher fields. The results of this calculation are in close agreement to the Bitter pattern experiments of Gammel et al. [Phys. Rev. Lett. 68, 3343 (1992)] assuming an anisotropy ratio γ of 5 and an in-plane penetration depth ${\lambda }_{\mathit{a}}$ of 1 413 Å, indicating that the vortex-chain state has been observed in these experiments.

The flux motion in a superconductor with a periodic logarithmiclike bare pinning potential is investigated. The effective barrier ${\mathit{U}}_{\mathit{J}}$(J) is derived and is shown to bear close resemblance with the related experimental results. The details of the pinning potential profile turn out to have significant influences on the functional form of the effective barrier. The linear response of the superconductor under a small current is analyzed and a slightly new formula is derived for resistivity in the thermally activated flux flow regimes. The distinct regimes for flux creep and flux flow and the crossover in between are treated simultaneously, and the familiar power-law behavior is demonstrated and is further confirmed by examining the dln E/dJ versus H relation. Satisfactory agreement is found between our results and related experimental observations. The experimentally observed field-dependent resistance broadening effect is also reproduced in this model.

The one- and two-phonon Raman-scattering spectrum of single-crystal ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{PrCu}}_3$${\mathrm{O}}_8$ is examined under resonance conditions. Strong features appear in the one-phonon spectrum at the positions of longitudinal optical (LO) infrared modes as the laser energy approaches that of the charge transfer gap. These Fröhlich-interaction-induced modes are accompanied by a second-order spectrum composed of overtones and combinations of the LO and ordinary Raman-allowed phonons. We examine the dependence on incident photon energy of both the line shape and center position of the highest-frequency two-phonon feature, which can be unambiguously attributed to a pure overtone of an infrared LO vibration. Due to the two-phonon nature of the scattering process the crystal momentum q is no longer restricted to small wave vectors and one can expect to observe effects of phonon dispersion. We find, indeed, changes in the line shape as the gap is approached, accompanied by a decrease in the center frequency to a value close to twice that of the q≊0 one-LO-phonon (1-LO) mode. A detailed comparison to the free electron theory for two-LO-phonon (2-LO) scattering by Zeyher [Phys. Rev. B 9, 4439 (1974)] is carried out. Relationships between the effective lattice mass characterizing the dispersion of this LO branch and the electron and hole effective band masses are established, and an estimate of the effective electron and hole band masses is made based on the magnitude of the phonon dispersion in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$ as measured by neutron-scattering experiments.

The t-J-model effective hopping integral is determined from the three-band Hubbard model for the charge carriers in ${\mathrm{CuO}}_2$ planes. For this purpose the values of the superexchange constant J and the charge-transfer gap ${\mathit{E}}_{\mathrm{gap}}$ are calculated in the framework of the three-band model. The energies of the local states for added electron and hole are obtained from the systematic analytical reduction of the three-band model and their kinetic energy is found from the accurate variational approach using the t-J model. Fitting values of J and ${\mathit{E}}_{\mathrm{gap}}$ to the experimental data allows us to narrow the uncertainty region of the threeband model parameters. As a result, the t/J ratio of the t-J model is fixed in the range 2.4–2.7 for holes and 2.5–3.0 for electrons. This approach explains the formation of the Frenkel exciton and correctly describes the main features of the charge-transfer spectrum.

The homologous series ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{2\mathit{n}+2+\mathrm{\delta }}$ (n=1,2,3,4) is the newest and most promising of the layered high-${\mathit{T}}_{\mathit{c}}$ superconducting materials, as demonstrated in setting the highest ${\mathit{T}}_{\mathit{c}}$ among the known superconducting materials. We slightly doped ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ with Pb, producing ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ with ${\mathit{T}}_{\mathit{c}}$ about 133 K. The Pb dopant helped material growth and still kept ${\mathit{T}}_{\mathit{c}}$ close to that of the optimally doped ${\mathrm{HgBa}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$. The superconducting transition temperature as a function of pressure, ${\mathit{T}}_{\mathit{c}}$(P), was measured to 3 GPa. ${\mathit{T}}_{\mathit{c}}$ increases monotonicaly with ${\mathit{dT}}_{\mathit{c}}$(P)/dP≊1.5 K/GPa near ambient pressure. The lattice parameters as a function of pressure were measured to 5 GPa. The volume decreases monotonically and is represented by an isothermal bulk modulus of ${\mathit{B}}_{\mathit{V}}$=143±15 GPa. Both results were combined to produce ${\mathit{T}}_{\mathit{c}}$(V), which is readily comparable to theoretical models.

We report an experimental setup of the ballistic-electron-emission microscope (BEEM) that is applicable to the study of thin free-standing metal films and metal-vacuum interfaces. We have used the technique to obtain spatially averaged BEEM spectra of thin free-standing gold films. Using such a spectrum, we obtained a rather coarse value of the work function for gold, which is compatible with some other reported values.

The thermopower (TEP) and electrical resistance of stoichiometric ${\mathrm{Fe}}_3$${\mathrm{O}}_4$ crystals have been measured up to pressures of 6 GPa over the temperature range of 80–160 K. The resistance decreases markedly with increasing pressure below the Verwey transition temperature ${\mathit{T}}_{\mathit{V}}$ and ${\mathit{T}}_{\mathit{V}}$ decreases linearly with increasing pressure. The magnitude of the TEP as well as the discontinuity at ${\mathit{T}}_{\mathit{V}}$ decrease with increasing pressure. The thermopower of ${\mathrm{Fe}}_3$${\mathrm{O}}_4$ shows an interesting upswing at low temperatures (<100 K) which is affected significantly by pressure.

Ultrasonic methods have been used to measure the polycrystalline elastic moduli of the Laves-phase pseudobinary compounds Zr(${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Fe}}_{1\mathrm{-}\mathit{x}}$${)}_2$ for 0.04≤x≤1.0. The bulk modulus decreases with increasing x up to the change from cubic (C15) to hexagonal (C14) structure at x=0.25. The shear modulus is essentially constant in the cubic phase. At the phase boundary the bulk modulus is about 6% higher in the hexagonal phase than in the cubic phase, while the shear modulus is the same in the two phases. As x increases in the hexagonal phase the bulk modulus decreases while the shear modulus increases. The softening of the bulk modulus in the cubic phase is correlated with the softening of the Fe bonding strength previously observed by nuclear methods, and with a sharp increase in the hydrogen capacity of these compounds. The stiffening of the shear modulus in the hexagonal phase may be correlated with the decrease of the hydrogen capacity in the corresponding compounds.

It is shown that for inhomogeneously broadened transitions Autler-Townes interactions can be resolved in the time domain by performing a modified echo experiment. Constructive and destructive interferences of the Autler-Townes components in electron spin triplet states are observed in the optically detected spin-echo amplitude decay signals for two different triplet-state color center model systems in calcium oxide and diamond crystals, respectively.

The average Gibbs energy per defect is approximately -${\mathit{k}}_{\mathit{B}}$T for any type of lattice defect in thermodynamic equilibrium. This result is independent of the defect, the material, and the environment, but requires the condition that a sufficient number of defects exist so that the Gibbs energy is changing slowly with number of defects at equilibrium while the defect concentration is small enough so that they do not interact.

By generalizing the Feynman-Vernon influence functional approach to a nonequilibrium system coupled to two reservoirs, we derive the generating functional for the nonequilibrium Green’s function. This generating functional is expected to have some applications in nonequilibrium transport problems since it consists of both the thermal information of the two reservoirs and the many-body effects of the test system.

The angular dependence of the circular magnetic x-ray dichroism (CMXD) at the ${\mathit{L}}_2$ and ${\mathit{L}}_3$ edges of grain-oriented R${\mathrm{Fe}}_2$ compounds has been studied to ascertain the multipolar nature of the features above and below the absorption edge. Within experimental error, all features in the CMXD spectra are consistent with dipole transitions between 2p core levels and the unoccupied spin-polarized states. We discuss some possible reasons for the apparent absence of the predicted quadrupolar angular dependence of the features below ${\mathit{E}}_{\mathit{f}}$.

We consider the parametric excitation of nonlinear magnetic waves by a uniform high-frequency magnetic field in the one-dimensional easy-plane (EP) and easy-axis (EA) ferromagnets. The problem is reduced to a perturbed nonlinear Schrödinger equation for the wave function of the Bose-condensed magnons. It is shown that close to the threshold of parametric instability a rotating localized distribution of longitudinal magnetization can be maintained in the form of a kink for EP and soliton for EA ferromagnets. The moving magnetic soliton can also be excited in EA ferromagnets. The conditions on intensity for generation within the transverse plane of a rotating domain wall are discussed. The results can also be applied to the Ni(${\mathrm{C}}_2$${\mathrm{H}}_8$${\mathrm{N}}_2$${)}_2$${\mathrm{NO}}_2$${\mathrm{ClO}}_4$ one-dimensional antiferromagnet. Information about the Haldane gap may be obtained from the conditions of kink generation.

It is shown that recently discovered effects of magnetic x-ray dichroism in angular-resolved photoemission from core levels of ferromagnets appear due to the spin-orbit and exchange splitting of core levels. The effects are proportional to the state multipoles characterizing the alignment and orientation of the hole levels, and can be observed with circularly polarized, linearly polarized, and unpolarized light. Possible applications of these effects in investigations of magnetic structures and adsorbates are pointed out.

An unrestricted Hartree-Fock (UHF) scheme is used to obtain approximate solutions of the Hubbard model on a Bethe lattice of infinite connectivity. The UHF energy yields a correct upper bound of the total energy over the whole phase diagram. In addition to the disappearance of antiferromagnetic long-range order away from half-filling, our results give a line separating the magnetic region of the phase diagram from the nonmagnetic one.

Using the ${\mathit{J}}_{1\mathrm{-}}$${\mathit{J}}_2$ model, we present a description of quantum phase transition from Néel ordered to the spin-liquid state based on the modified spin-wave theory. The general expression for the gap in the spectrum in the spin-liquid phase is given.

The cubic temperature dependence of the nuclear relaxation rate (NRR) in layered superconductors with the order parameter having zeros at the Fermi surface (FS) is found to be universal under quite general conditions. The coefficient in the quasi-Korringa term for the NRR appearing at low temperatures due to impurity scattering is estimated. It is shown that an anisotropy of the gap function over the FS leads to the disappearance of the Hebel-Slichter coherence peak close to ${\mathit{T}}_{\mathit{c}}$. The corresponding analysis of the widely accepted model [D. Thelen et al., Phys. Rev. B 47, 9151 (1993)] for the Y-Ba-Cu-O system is presented.

The dynamics of one-dimensional arrays of parallel coupled Josephson-junction ladder arrays in a random magnetic field is described. The fluctuation of superconducting phase difference becomes constant above the roughening transition current ${\mathit{I}}_{\mathit{c}2}$, and grows linearly in time for ${\mathit{I}}_{\mathit{c}1}$<I<${\mathit{I}}_{\mathit{c}2}$, where ${\mathit{I}}_{\mathit{c}1}$ is the usual critical current separating zero voltage and finite voltage regimes. The characteristic time ${\mathit{t}}^{\mathrm{*}}$(I) diverges as (${\mathit{I}}_{\mathit{c}2}$-I${)}^{\mathrm{-}\gamma }$ when I approaches ${\mathit{I}}_{\mathit{c}2}$ from below. The discontinuity of dV/dI at ${\mathit{I}}_{\mathit{c}2}$ and the absence of hysteresis above ${\mathit{I}}_{\mathit{c}2}$ in I-V curve are also discussed.