We extend spin-polarized photoelectron diffraction to the direct imaging of magnetic spin configurations by using holographic-inversion methods. Theoretical calculations for ${\mathrm{Mn}}^{2+}$ and ${\mathrm{O}}^{2\mathrm{-}}$ ions in linear chains show that it is possible via two different spin-selective image functions to determine both the positions and orientations of magnetic scatterers relative to a given type of emitter. Such holographic images thus should provide direct information on short-range magnetic spin configurations near surfaces.

We have studied the electronic structure of the superconductor ${\mathrm{YNi}}_2$${\mathrm{B}}_2$C by photoemission and inverse-photoemission spectroscopy. The spectra show a prominent Ni 3d band centered around 1.5 eV below the Fermi level (${\mathit{E}}_{\mathit{F}}$), whose top crosses ${\mathit{E}}_{\mathit{F}}$, and B, C 2sp-derived states at higher binding energies, generally consistent with band-structure calculations. However, the Ni 3d-derived conduction bands are narrower than calculated and are accompanied by a satellite, signaling electron-correlation effects within the d bands. The density-of-states peak at ${\mathit{E}}_{\mathit{F}}$ predicted by band-structure calculations is suppressed and its spectral weight is transferred away from ${\mathit{E}}_{\mathit{F}}$, presumably due to an electron-phonon interaction and/or electron correlation.

We present the observation of Josephson self-coupling in $\frac{\frac{\mathrm{Nb}}{\mathrm{Al}{\mathrm{O}}_x}}{\mathrm{Nb}}$ tunnel junctions. In current-voltage characteristics, anomalous subharmonic gap structures were observed; steep current steps and peaks which were sensitive to the magnetic field appeared at the voltages of $\frac{2\Delta }{3e}$ and $\frac{2\Delta }{5e}$. The characteristics of these structures could not be explained by multiparticle tunneling and/or multiple Andreev reflection. We conclude that the structures at $\frac{2\Delta }{3e}$ and $\frac{2\Delta }{5e}$ are due to Josephson self-coupling.

Neutron-diffraction techniques have been used to study the interplay between superconductivity and magnetism in ${\mathrm{HoNi}}_2$${\mathrm{B}}_2$C (${\mathit{T}}_{\mathit{c}}$=8 K). The experimental results, obtained on single crystals, show that below approximately 4.7 K, this compound is in a simple antiferromagnetic state that coexists with superconductivity. Between approximately 4.7 and 6 K, an incommensurate modulated magnetic structure has been found. This observation strongly suggests that pair breaking associated with this incommensurate magnetic structure is responsible for the deep minimum in ${\mathit{H}}_{\mathit{c}2}$ and the near-reentrant behavior observed in this compound at approximately 5 K.

We have measured the complex conductivity of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ single-crystal thin films using coherent THz spectroscopy. We obtain directly the London penetration depth, the plasma frequency ${\mathrm{\omega }}_{\mathit{p}}$, and the quasiparticle scattering rate 1/τ. We find that 1/τ drops rapidly with temperature below ${\mathit{T}}_{\mathit{c}}$ in all the superconducting samples, implying that this is a signature of high-${\mathit{T}}_{\mathit{c}}$ superconductivity. ${\mathrm{\omega }}_{\mathit{p}}$ decreases with increasing x, indicating that Pr takes mobile carriers from the CuO planes. Both the THz and dc conductivity yield evidence for the opening of a spin gap above ${\mathit{T}}_{\mathit{c}}$.

A fermion model consisting of two chains with interchain tunneling is formulated and solved exactly by the Bethe-ansatz method. The interchain tunneling leads to Cooper-pair-like bound states and a threshold energy is required to overcome the binding energy. The correlation functions manifest superconducting properties.

By using a miniature two-coil mutual-inductance method and an exact inversion scheme, the ac penetration depth ${\lambda }_{\mathrm{ac}}$ was measured in a twinned ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ crystal in dc fields parallel to the c axis. The Ohmic dc resistance was also measured on the same crystal. The behavior of these quantities was altogether consistent with the vortex-glass-transition scaling. However, if we calculate the Labusch parameter and the pinning relaxation time from ${\lambda }_{\mathrm{ac}}$, they show unexpectedly large frequency dependencies, which can hardly be explained by the standard theory of the linear ac response of pinned vortices.

We measured the current-induced loss of vortex correlation in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ crystals using the pseudo-dc-flux-transformer geometry. We find that the current density ${\mathit{J}}_{\mathrm{cut}}$ at which the top and bottom voltage drops differ is a linear function of temperature, is independent of pinning, and depends on the thickness of the sample. This thickness dependence strongly suggests that the electrical current flows at the surface of the sample. The observed behavior with temperature, magnetic field, and thickness is described by a phenomenological model.

Magnetic ordering has been investigated by means of neutron scattering in an $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ single crystal prepared with two different oxygen concentrations, $x=0.1\mathrm{}$ and $x=0.18\mathrm{}$, and in an aluminum-doped $\mathrm{Y}{\mathrm{Ba}}_2\left({\mathrm{Cu}}_{3-y}{\mathrm{Al}}_y\right){\mathrm{O}}_{6+x}$ crystal with $x=0.25\mathrm{}$ and $y=0.14\mathrm{}$. For the undoped crystal, a magnetic ordering transition was observed at $T_N=410\mathrm{}$ (respectively for $x=0.1\mathrm{}$ and $x=0.18\mathrm{}$), but no second magnetic transition was found down to 2 K. In contrast, an antiferromagnetic reordering was observed for the aluminum-doped sample with a transition temperature $T_2=8\mathrm{}$ K. This implies a high sensitivity of this second phase to impurities and indicates that the transition is not necessarily an intrinsic property of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$.

Fluorescence and excitation spectra of ${\mathrm{Cm}}^{3+}$ diluted in ${\mathrm{ThO}}_2$ powder are reported at room and low temperatures. The observed ${\mathrm{Cm}}^{3+}$ spectra are from the cubic symmetry lattice site and are assigned to phonon-assisted electric dipole transitions and to magnetic dipole transitions. From these assignments, the crystal-field parameters ${\mathit{B}}_0^4$=-6436 ${\mathrm{cm}}^{\mathrm{-}1}$ and ${\mathit{B}}_0^6$=1195 ${\mathrm{cm}}^{\mathrm{-}1}$ have been determined. The experimental energy levels for the ground term (∼80% ${}_{}{}^8{}_{}{}^{}$${\mathit{S}}_{7/2}$) determined from the optical data and earlier electron paramagnetic resonance spectra are in good agreement with the calculated values.

Photoconductive currents of the same order of magnitude as in conventional impurity-doped semiconductors have been observed at temperatures lower than 80 K in the ${\mathrm{K}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Li}}_{\mathit{x}}$${\mathrm{TaO}}_3$ (KTL) mixed system (with 0.016≤x≤0.05) and under light illumination with energy lower than the band gap. The dependence of the photoconductivity on temperature, Li concentration, and external electric field as well as on sample history and treatment is studied. The results are interpreted and discussed on the basis of a model allowing a calculation of the impurity levels taking into account the displacement of the oxygen ions nearest to the off-center position of the ${\mathrm{Li}}^{+}$.

The effects of thermal order-parameter fluctuations on the NMR line shape of incommensurate systems are evaluated within the mean-field Landau theory and the results are compared with the ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ 1/2→-1/2 NMR spectra of ${\mathrm{Rb}}_2$${\mathrm{ZnCl}}_4$ and ${\mathrm{K}}_2$${\mathrm{SeO}}_4$ just below the paraelectric-incommensurate transitions. We show that thermal fluctuations do not only reduce the effective incommensurate splitting as compared to the static case but also change the shape of the spectrum. In particular they remove the δ-function-like form of the two edge singularities in analogy to the Debye-Waller factor in x-ray scattering. Two-dimensional NMR separation techniques allow for a separate observation of static and dynamic incommensurate line shapes close to the paraelectric-incommensurate transition temperature ${\mathit{T}}_{\mathit{I}}$. The static inhomogeneously broadened NMR line shape results from the static distribution of quadrupole-perturbed Zeeman frequencies, reflecting the frozen-out incommensurate modulation wave. The dynamic line shape reflects the time-dependent part of the electric quadrupole interaction resulting from phason and amplitudon thermal fluctuations of the modulation wave. Close to ${\mathit{T}}_{\mathit{I}}$ these fluctuations become so low in frequency that they influence the line shape. A precise determination of ${\mathit{T}}_{\mathit{I}}$ can be obtained from the maximum in the width of the dynamic line shape.

A systematic study of ${}_{}{}^{57}{}_{}{}^{}\mathrm{ion}$ implantation in cupric and cuprous oxide films has been reported. The CuO and ${\mathrm{Cu}}_2$O films having excellent stoichiometry were prepared by the technique of laser ablation. The phases formed in the implanted and thermally annealed samples were characterized by Mössbauer spectroscopy and glancing angle x-ray diffraction. For the as-implanted CuO films the ${\mathrm{Cu}}_6$${\mathrm{Fe}}_3$${\mathrm{O}}_7$, ${\mathrm{CuFeO}}_2$,β-${\mathrm{CuFeO}}_2$, and ${\mathrm{Cu}}_2$O phases are detected. The same phases are present in the ${\mathrm{Cu}}_2$O-implanted films with some ${\mathrm{Cu}}_2$O⋅FeO units, metallic Cu atoms, and ${\mathrm{Cu}}_{\mathit{x}}$${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$${\mathrm{O}}_4$ spinel in addition. Annealing at 400 °C under argon atmosphere produces in both the cases a strong increase of the ${\mathrm{CuFeO}}_2$ and β-${\mathrm{CuFeO}}_2$ phases at the expense of the ${\mathrm{Cu}}_6$${\mathrm{Fe}}_3$${\mathrm{O}}_7$ phase. This latter phase completely vanishes after annealing at 500 °C and new phases, namely α-${\mathrm{Fe}}_2$${\mathrm{O}}_3$ and small iron clusters appear. The amount of the ${\mathrm{Cu}}_{\mathit{x}}$${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$${\mathrm{O}}_4$ phase continues to increase after annealing at 500 and 600 °C, whereas ${\mathrm{CuFeO}}_2$ decreases. The α-${\mathrm{Fe}}_2$${\mathrm{O}}_3$ contribution disappears after annealing at 600 °C.

We report on an experimental study of indium and niobium impurity distributions in NiNbIn dilute alloys by combining the perturbed-angular-correlation (PAC) technique with extended x-ray-absorption fine-structure (EXAFS) measurements on both the indium and niobium K edges at room temperature. Our EXAFS results show that around the indium or niobium central atom, the first-shell coordination number is strongly reduced with respect to a pure nickel environment. Whereas niobium is found in the first shell around niobium in small cluster configurations, indium is found at larger distances from indium indicating a repulsive In-In interaction. No close mixing between these two impurities was detected, confirming the strong In-Nb repulsion. These findings are fully consistent with the conclusions drawn from the data obtained in an earlier as well as the present PAC study.

A systematic study of the temperature-dependent absorption spectra of ${\mathit{F}}_{\mathit{H}}$ (${\mathrm{CN}}^{\mathrm{-}}$) defect pairs in a CsCl host crystal is presented. At the lowest temperatures, two distinct absorption peaks are observed. As the temperature is increased, the separation of the peaks decreases, the relative oscillator strengths change, and the peaks broaden. These experimental results are explained by a simple model which considers that the nearly degenerate 2s and 2${\mathit{p}}_{\mathit{z}}$ electronic states of the F center are strongly mixed by the intrinsic and displacement dipole moments of the ${\mathrm{CN}}^{\mathrm{-}}$ molecule. From this study, one obtains important parameters such as coupling constants, effective phonon mode frequencies participating in the absorption process, and a parameter describing the degree of 2s-2${\mathit{p}}_{\mathit{z}}$ mixing, which are crucial for testing the physical models proposed for the electronic to vibrational energy-transfer process in this defect system.

We report on a systematic study of Ne-projectile and Na-target atom autoionization electron emission during 700-eV ${\mathrm{Ne}}^{+}$ ion bombardment of polycrystalline Cr, Cu, Mo, and Pt surfaces covered with an increasing amount of Na. We show that the collisionally excited Ne 2${\mathit{p}}^4$${(}^1$D) singlet core can be efficiently converted to a 2${\mathit{p}}^4$${(}^3$P) triplet through an Auger rearrangement process involving a solid valence electron and that the conversion is highly localized at the excitation site and its rate is strongly dependent on local electronic properties. We found that the Na 2p electron excitation essentially results from an L-shell vacancy transfer from the Ne 2${\mathit{p}}^4$${(}^1$D) at low Na coverages and from direct excitation in Na-Na symmetric collisions at high coverages. We demonstrate the great potential of the low-energy collisionally excited autoionization electron spectroscopy as a surface-analysis technique in alkali-metal adsorption studies.

The positron-lifetime spectra and the resistivity in La-doped ${\mathrm{BaTiO}}_3$ have been measured at room temperature for La content of 0–0.8 at. %. It was found from the experiments that with increasing La content, the variation of both the positron-lifetime parameters and the resistivity are nonmonotonic. The nonmonotonic dependence of positron-lifetime parameters on the La content is explained by an associated-defect model, in which a small critical region of La content is proposed. With an increase of La content Ba vacancies induced by La doping appear mainly in isolated form below the critical region, while above the critical region the associated defect (${2\mathrm{L}\mathrm{a}}_{\mathrm{Ba}}^{\mathrm{\cdot }}$${\mathrm{V}}_{\mathrm{Ba}}^{\mathrm{″}}$) forms quickly. The associated defect may have no ability to trap positrons.

The low value of (${\mathit{T}}_{\mathit{c}}$-${\mathit{T}}^{\mathrm{*}}$)/${\mathit{T}}_{\mathit{c}}$≊0.1%, where ${\mathit{T}}_{\mathit{c}}$ is the nematic-isotropic phase-transition temperature and ${\mathit{T}}^{\mathrm{*}}$ is the temperature at which the light-scattering intensity diverges in the supercooled isotropic phase for the nematic-isotropic transition is a long-standing puzzle. We show in this paper that by extending the renormalization-group calculation to second order of ɛ and, alternatively, by considering that the nematic-isotropic transition is close to the tricritical point, considerable improvement over previous results is possible.