The properties of Nb, Mo, and Cr as the spacers in magnetic/nonmagnetic multilayers are examined. Utilizing the simple Ruderman-Kittel-Kasuya-Yosida-like response-function theory, one can elucidate not only which features of the bulk band structures are relevant but also discuss the implications of the spacers being inhomogeneously strained. The crucial question proves to be determining which caliper can resist all the broadening effects to appear actually as a macroscopic quantum effect. One mechanism is to minimize scattering by selecting wave functions with substantial s and p character. Another is to maximize the effective velocity and thereby minimize dephasing by the existing scattering. In Nb(110) and Mo(100), such considerations select Kohn-anomaly calipers which arise from the N-centered ellipses. Consideration of resilience to scattering effects is crucial to explaining why the Mo(100) repeat distance appears at three layers instead of at the two layers as seen in Cr. The uniform long repeat distances seen in Cr for the (100), (211), and (110) and the (110) repeat distance in Mo appear to be internally consistent in that they occur from the rim of the Δ centered lens surfaces and involve the strong mixing of ${\mathit{t}}_{2\mathit{g}}$ and ${\mathit{e}}_{\mathit{g}}$ d states. The analysis also suggests several factors which help to understand the systematics observed for spacers across the transition series.

The electronic structure and the ensuing magnetic properties of γ-Fe and ${\mathrm{Fe}}_3$Pt Invar are determined using the local approximation to spin-density-functional theory and the augmented-spherical-wave method. A noncollinear constrained-moment procedure is described and employed to obtain the total energy as a function of the volume and the magnetic moment arranged both in collinear and noncollinear spiral structures. This, on a microscopic basis, establishes the connection of the volume with longitudinal and transverse spin fluctuations. We determine the thermal expansion coefficients of γ-Fe and ${\mathrm{Fe}}_3$Pt and give an explanation of their anomalous magnetovolume properties.

It is argued that dislocations in the L$1_2$ intermetallic compounds displaying the yield strength anomaly undergo a stress-driven pinning-depinning transition. The transition is from a dynamic phase in which a moving dislocation becomes immobile to a dynamic phase in which a moving dislocation, in an infinite medium, remains mobile for all time. The distribution of event times and areas, where an ‘‘event’’ is the mobilization and subsequent immobilization of a dislocation, is related to measurements of the primary creep transient. At the critical point of the proposed transition, the distribution of events becomes scale invariant. A simple scaling hypothesis connects the scaling behavior of the transition to the time dependence of the creep tests. A simplified model of dislocation motion is presented and used to study the properties of the transition. The properties so calculated are not obviously consistent with the published interpretations of experiments, but are consistent with the published data. A reinterpretation of those experiments is proposed.

The problem of an isolated ion with the total angular momentum J in cubic metals is considered using the Abrikosov pseudofermion technique. The system of generalized kinetic equations is derived. An example of J=5/2 in the case of the ${\mathrm{\Gamma }}_8$ quartet ground state is considered (${\mathrm{CeB}}_6$). It is shown that the central peak of the susceptibility is described by two Lorentzians one of which is higher and narrower than the other. In the first approximation both linewidths have the Korringa form. It is shown that such a multimode central-peak structure is a rather general phenomenon if the degenerate manifold is not a Kramers doublet and the system has some extra excited states.

The S=1/2XXZ spin chain with the staggered XY anisotropy H=J${\sum }_{\mathrm{n}}^{\mathrm{N}}$(${\mathrm{S}}_{\mathrm{n}}^{\mathrm{x}}$${\mathrm{S}}_{\mathrm{n}+1\mathrm{}}^{\mathrm{x}}$+${\mathrm{S}}_{\mathrm{n}}^{\mathrm{y}}$${\mathrm{S}}_{\mathrm{n}+1\mathrm{}}^{\mathrm{y}}$+Δ${\mathrm{S}}_{\mathrm{n}}^{\mathrm{z}}$${\mathrm{S}}_{\mathrm{n}+1\mathrm{}}^{\mathrm{z}}$)- δ${\sum }_{\mathrm{n}}^{\mathrm{N}}$(-1${)}^{\mathrm{n}}$(${\mathrm{S}}_{\mathrm{n}}^{\mathrm{x}}$${\mathrm{S}}_{\mathrm{n}+1\mathrm{}}^{\mathrm{x}}$-${\mathrm{S}}_{\mathrm{n}}^{\mathrm{y}}$${\mathrm{S}}_{\mathrm{n}+1\mathrm{}}^{\mathrm{y}}$) is shown to possess gapless, Luttinger-liquid-like phases in a wide range of its parameters: the XY-like phase and spin nematic phases, the latter characterized by a two-spin order parameter breaking translational and spin rotation symmetries. In the simplest, exactly solvable case Δ=0, the spectrum remains gapless at arbitrary J and δ and is described by two massless Majorana (real) fermions with different velocities ${\nu }_{\pm }$=‖J±δ‖. At ‖δ‖<J the staggered XY anisotropy does not influence the ground state of the system (XY phase). At ‖δ‖>J, due to level crossing a spin nematic state is realized, with ↑↑↓↓ and ↑↓↓↑ local symmetry of the xx and yy spin correlations. The spin corelation functions are calculated and the effect of thermally induced spin nematic ordering in the XY phase (‘‘order from disorder’’) is discussed. The role of a finite Δ is studied in the limiting cases ‖δ‖≪J and ‖δ‖≫J, using the bosonization method. On the basis of the derived self-dual field-theoretical model, similar to the one recently proposed to treat two weakly coupled Luttinger chains, a confinement regime is described, in which fermionic excitations fail to be observable due to Luttinger-liquid effects. Kosterlitz-Thouless transitions to massive phases, driven by the δ anisotropy, are discussed.

The theory of flux flow developed by Bardeen and Stephen (BS) is modified and extended to the high-field case. The Clem model and Wigner-Seitz circle-cell approximation for vortices are used in our approach. The distinct boundary of the normal core of a vortex in BS theory is removed and treated naturally. Several interesting results come out as a consequence. The Lorentz force is determined by the normal current rather than the supercurrent. But the supercurrent can sustain the magnetic-field distribution of flux quanta. From energy dissipation considerations, the Lorentz force is equal to viscosity force automatically without assumption as made in BS theory. An expression for the viscosity is also obtained.

We consider an SNS junction, N being the two-dimensional electron gas, subjected to a magnetic field exceedingly large for weak superconductivity. We show that under the condition of Landau quantization the proximity effect induces a thin superconducting paramagnetic strip near the boundary of the N region. We obtain the expression for the supercurrent that accounts for multiple Andreev scattering of magnetic edge states. We also address Josephson coupling by bulk magnetic states.

The Goldstone-Feynman diagrammatic technique is adopted to study the interaction between mixed-valent rare-earth impurities in BCS superconductors. The influence of cerium-impurity coupling together with isolated cerium-impurity upon superconductivity of ${\mathrm{Th}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$ system is worked out. In comparison with magnetic rare-earth impurities, depression of superconductivity due to impurity interaction of nonmagnetic mixed-valent rare-earth dopants is much smaller.

Precise measurements of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ melting pressure in several magnetic fields have been made through the various magnetic ordering transitions. Throughout the low-field phase, we find a ${\mathit{T}}^4$ temperature dependence of the melting pressure, characteristic of antiferromagnetic spin waves with linear dispersion and a velocity of 7.8 cm/s, almost independent of field. However, the melting pressure in the high-field phase (HFP) deviates from the ${\mathit{T}}^4$ dependence near the HFP-paramagnetic phase transition, resulting in a very rapid entropy change near ${\mathit{T}}_{\mathit{c}}$. The spin-wave velocity increases with field, consistent with a strong temperature dependence of the magnetization. The entropy and magnetization discontinuities across the various phase boundaries have been determined. All results are thermodynamically consistent with the measured magnetic phase diagram.

We have fabricated superconducting weakly coupled wire networks made in thin amorphous niobium-silicon films of high normal-state resistivity and have investigated vortex dynamics in these networks. For the temperatures of interest, the wires have a width in the order of, and a length much larger than the Ginzburg-Landau (GL) coherence length. We find that the vortex mobility in the wire networks is much lower than in Josephson junction arrays. The ratio of the length of the single wires to the GL coherence length determines whether a Kosterlitz-Thouless-Berezinskii transition can be observed in zero field, as well as oscillations at low temperatures in the magnetoresistance. At low temperatures the critical current does not show oscillations in a magnetic field, which might be a consequence of the existence of special vortex configurations in networks with a linear current-phase relation.

A superconducting transition around 15–16 K is reported for metastable, as-melted ${\mathrm{ScNi}}_2$${\mathrm{B}}_2$C samples. Zero resistivity ${\mathit{T}}_{\mathit{c}}$(zero) was observed at 14.6 K with ${\mathit{T}}_{\mathit{c}}$(onset) around 16.5 K. A consistent diamagnetic ${\mathit{T}}_{\mathit{c}}$ signal was observed around 14.8–15.6 K. The new superconducting phase was identified as isostructural to the quaternary ${\mathrm{LuNi}}_2$${\mathrm{B}}_2$C-type phase with tetragonal lattice parameters a=3.34 Å and c=10.2 Å. This superconducting phase is unstable due to the extremely small ${\mathrm{Sc}}^{3+}$ ionic size, where the Sc atom is located in the cavity formed by the B-Ni-B-C network and no superconducting transition could be observed down to 5 K after 1050 °C annealing.

This paper presents a macroscopic theory for analyzing the magnetoelastic response of elastic type-II superconductors in the mixed state. The theory includes not only the vortex-dynamic effect, the normal-current effect, and the flux-flow Hall effect, but also the effect of the London moment induced by the local motion of the deformable superconductor in the mixed state. The theory is considered to be valid within the framework of the generalized Galilean relativity at the magnetoquasistatic approximation. By this theory, a set of linearized coupled wave equations is derived to study some problems concerning magnetoelastic wave propagation in type-II superconductors in the mixed state. Attenuation and dispersion behaviors of the magnetoelastic wave are then analyzed. It is shown that the nonlocal effect on the length scale of the London penetration depth may be of importance in analyzing the propagation behavior of the magnetoelastic wave at frequencies higher than the depinning frequency. It is also shown that the effect of the London moment induced by dynamic deformation can be of significance as compared with the effect of the normal Lorentz current on the magnetoelastic coupling behavior of elastic type-II superconductors in the mixed state. Furthermore, it is found that there is a phase change between the transverse elastic wave and the magnetic wave induced in the type-II superconductor in the mixed state. This effect is found to be closely related to the vortex-dynamic properties of the superconductor.

We study the order of the zero temperature quantum phase transitions at density ρ=1 in the one-dimensional extended boson Hubbard model by examining the order parameter distribution and hysteresis effects. The phase diagram of the model at ρ=1/2, a generalization of the spin-1/2 XXZ Hamiltonian, is also obtained, and the possibility of a supersolid region is discussed.

A scanning tunneling microscope has been used to study the different conductance regimes of superconducting Pb junctions of atomic size. Measurement of the apparent tunneling barrier and imaging of probed areas before and after the spectroscopic measurement give information on the surface condition and the geometry of the junction. The evolution of the differential conductance curves is followed from the tunneling regime to contact as the junction is varied in a continuous and controlled manner. The oberved evolution of the conductance follows quantitatively Octavio-Tinkham-Blander-Klapwijk theory with the addition of a lifetime broadening parameter, which accounts for the observed smearing of the superconducting gap features.

Applying the bosonization procedure to constrained fermions in the framework of the one-dimensional t-J model, we discuss a scenario of singlet superconductivity in a lightly doped double chain where all spin excitations remain gapful.

We have measured the magnetoresistivities of crystalline disordered ${\mathrm{Ti}}_{1-x}{\mathrm{Al}}_{x-y}{(\mathrm{S}\mathrm{n},\mathrm{C}\mathrm{o})}_y$ $x=0.072\mathrm{} \mathrm{and} y\le 0.03$ alloys between 1.7 and 15 K in magnetic fields up to 3 T. With a total doping level of 7.2 at.% for Ti, our samples are disordered enough to manifest quantum corrections due to weak-localization and electron-electron interaction effects. As the magnetic field $B$ is increased, magnetoresistivities $\frac{\Delta \rho \mathrm{}\left(B\right)\mathrm{}}{\rho \mathrm{}\left(0\right)\mathrm{}}=\frac{\left[\rho \mathrm{}\right(B)-\rho \mathrm{}(0\left)\right]}{\rho \mathrm{}\left(0\right)\mathrm{}}$ of the order of ${10}^{-4\mathrm{}}$-${10}^{-3\mathrm{}}$ are observed. Both the functional forms and magnitudes of the observed $\Delta \rho \mathrm{}\left(B\right)\mathrm{}$ are interpreted in terms of weak-localization and Maki-Thompson superconducting fluctuation effects. Our sample compositions (i.e., additions of $y=0.000, 0.030$ of Sn, and 0.0005 of Co, respectively, for Al) have been chosen so as to tailor the various aspects of both effects. We find that spin-orbit scattering is greatly increased in the alloy containing 3.0 at.% of Sn. As a result, $\Delta \rho \mathrm{}\left(B\right)\mathrm{}$ increases monotonically with increasing $B$ in all our measuring magnetic fields and at all measuring temperatures. In the alloy containing 0.05 at.% of Co, superconducting fluctuation effects are greatly enhanced at our measuring temperatures, and a diverging inelastic scattering rate is observed in our lowest temperature range of 1.7-1.9 K. From comparison of our experimental results with theory, the inelastic scattering times have been inferred and ascribed to electron-phonon interaction in the presence of strong impurity scattering. Our results suggest that, in the crystalline disordered metals like our Ti-Al-(Sn,Co) alloys, the electron-phonon scattering rate varies with the square of the temperature, ${\tau }_{\mathrm{ph}}^{-1\mathrm{}}\sim T^2$, in the temperature range 3-15 K. Particularly, the absolute magnitudes of the measured ${\tau }_{\mathrm{ph}}$ are consistent within ∼40% with the theoretical prediction.

The current-voltage characteristics of ultrasmall Josephson junctions sensitively depend on the electromagnetic environment of the junction. When the charging energy exceeds the Josephson coupling energy, the usual supercurrent at zero voltage is completely suppressed. However, for typical environmental impedances, which are small compared to the resistance quantum, stochastic Cooper-pair tunneling leads to a supercurrent peak at a small finite voltage which is proportional to the temperature and the low-frequency resistance of the external circuit. An analytic expression for the form of this universal peak, which is independent of the high-frequency behavior of the environment, is given. With increasing Josephson coupling the peak merges into the usual supercurrent of a Josephson junction. At larger voltages the Cooper-pair current depends on details of the environment. Current peaks are shown to result from resonances in the environmental impedance. Specifically, the case of an LC transmission line of finite length is discussed.

Conserving approximations are applied to the attractive Holstein and Hubbard models (on an infinite-dimensional hypercubic lattice). All effects of nonconstant density of states and vertex corrections are taken into account in the weak-coupling regime. Infinite summation of certain classes of diagrams turns out to be a quantitatively less accurate approximation than truncation of the conserving approximations to a finite order, but the infinite summation approximations do show the correct qualitative behavior of generating a peak in the transition temperature as the interaction strength increases.

We have investigated the ground state of an electron-phonon system with strong electron-phonon interaction and a weak on-site Coulomb repulsion using the correlated squeezed-state approach. We have introduced a variational ground state in which the phonon subsystem is in a correlated squeezed state and the electron subsystem is in a superconducting pairing state. In addition to the anharmonicity of each phonon mode induced by the linear coupling with the electrons, the correlated squeezed state is able to take into account the nonlinearity of the induced interaction between different phonon modes beyond the Hartree approximation. Also, with optimal values of the variational parameters this trial state will by construction yield an energy lower than those obtained in previous studies, and thus our variational ansatz is a more stable ground state for this system. Furthermore, in this approximate ground state the reduction effect of phonons is much more alleviated, and thus the mass enhancement inherent to the polaron effect is considerably weakened. This weakening of the reduction effect should, in turn, affect other physical properties of the system; for instance, it does suggest the possibility of higher critical temperatures for superconductivity in the strong-coupling limit where the superfluidlike bipolaronic superconductivity is supposed to occur.

We report an observation of the ${}_{}{}^{63,65}{}_{}{}^{}\mathrm{Cu}$ nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) in ${\mathrm{Y}}_2$${\mathrm{Ba}}_4$${\mathrm{Cu}}_7$${\mathrm{O}}_{15}$. We have measured the temperature dependence of the Cu NQR frequency and spin-lattice relaxation at all four chemically inequivalent Cu sites, and of the Cu magnetic shift at two inequivalent plane Cu sites (for the magnetic field parallel and perpendicular to the c axis). The ${\mathrm{Y}}_2$${\mathrm{Ba}}_4$${\mathrm{Cu}}_7$${\mathrm{O}}_{15}$ compound turns out to be a structure containing two inequivalent ${\mathrm{CuO}}_2$ planes of differing doping levels, a multilattice in which ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ blocks and ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ blocks alternate. In the normal conducting state both the static and the dynamic electron spin susceptibilities of the individual planes of a double plane are governed by the same temperature dependence, which shows a behavior typical for an underdoped high-${\mathit{T}}_{\mathit{c}}$ compound. The same temperature dependence means strong coupling between these planes, with the lower limit of the coupling constant not much less than 30 meV. Although the planes are strongly coupled, their spin susceptibilities retain a distinct q dependence. The temperature variation of relaxation rate and Knight shift is described in terms of spin-gap formation or, alternatively, of frustrated phase separation. Below ${\mathit{T}}_{\mathit{c}}$, the common temperature dependence is lost, which could arise from the opening of two superconducting gaps that differ in the individual planes.