Measurements of the surface-acoustic-wave (SAW) attenuation and dc resistance of several amorphous superconducting In/${\mathrm{InO}}_{\mathit{x}}$ films as a function of temperature exhibit an excess SAW attenuation below the Kosterlitz-Thouless transition temperature, which cannot be accounted for by the presence of flux-flow resistance due to unbound vortices in these films. Qualitative agreement with the observed SAW attenuation below the Kosterlitz-Thouless temperature may be obtained by using a model based on the attenuation produced by bound vortex pairs present in the films below the Kosterlitz-Thouless transition temperature.

A model explaining the presence of a periodic train of microwave absorption lines in the magnetic modulated microwave absorption (MMMA) spectra of high- and low-temperature superconductors is proposed. The model assumes the occurrence of regular superconducting current loops, closed by Josephson junctions, in these materials. The system of such loops is considered within the basic model of the rf superconducting quantum interference device taking into account the effect of thermal fluctuations. The magnetic-field and temperature dependencies of the MMMA obtained on the basis of the proposed model are in qualitative agreement with experimental data.

The creation of a Cooper-pair mass spectroscopy is suggested. The plasmons in low-dimensional superconductor structures (layers or wires in the dielectric background) are theoretically considered for this purpose. The Cooper-pair mass ${\mathit{m}}^{\mathrm{*}}$ (the parameter ${\mathit{m}}^{\mathrm{*}}$ in London electrodynamics) can be determined by measurements of the Doppler shift of the plasmon frequency when a direct current is applied through the superconductor. The plasmons with frequency ω lower than the superconducting gap 2Δ can be detected by the same far-infrared absorption technique and grating coupling used previously for investigation of two-dimensional plasmons in semiconductor microstructures and polaritons in condensed-matter physics.

The creation of contactless Cooper-pair mass spectroscopy based on the Bernoulli-Venturi effect in thin superconducting films is suggested. The preparation of layered metal-insulator-superconductor-type heterostructures and standard electronics are necessary for the realization of the method. Two electrodes are patterned from the metallic layer: a circle and concentric-ring electrode. The currents in the superconducting film are induced by a drive coil concentric to the electrodes. The Bernoulli potential of the charged Cooper-pair superfluid creates a measurable electric polarization of gate electrodes of this plane-capacitor device. The current-induced contact-potential difference is limited by the Ginzburg-Landau potential -${\mathit{a}}_{\mathrm{GL}}$(T)= 1/2ħ${\mathit{e}}^{\mathrm{*}}$${\mathit{H}}_{\mathit{c}2}$(T)/${\mathit{m}}^{\mathrm{*}}$c=${\mathrm{ħ}}^2$/2${\mathit{m}}^{\mathrm{*}}$${\xi }^2$(T). The additional charge of the polarized circular electrode has the same sign as the free charge carriers of the superconductor.

Superconducting networks and superfluid films in two dimensions are often described by a theoretical model in which the unique microscopic variables are phases. Among these models the XY model with Villain’s interaction potential can be mapped exactly onto a lattice Coulomb gas. This is well known, but several questions still have no clear answers: First, what is the meaning of the charge of the Coulomb gas in terms of the original variables of the XY model? Second, how can the helicity modulus be expressed exactly in the Coulomb gas representation on a finite torus? In this paper we answer these questions. The mapping onto a lattice Coulomb gas is done in a way that differs from the usual one. This mapping is applied to a phase model whose partition function has an identical mathematical structure as the one of the XY model with Villain’s interaction. For this phase model, contrary to the XY model, the charges of the Coulomb gas describe indeed exactly the topological charges as we can define them in terms of the phase variables. However, this Coulomb gas contains an additional polarization energy and two additional fictitious variables accounting for the specific topological character of the torus. The helicity modulus is exactly the inverse of a dielectric constant which can be defined as the linear response to an external uniform electric field, even on a torus. The meaning of the Coulomb-gas representation is also discussed in terms of the original variables of the XY model.

In order to explore a correlation between superconductivity and the electronic structure of Ni-based superconducting quaternary compounds, a systematic investigation of the electronic structures for ${\mathrm{YNi}}_2$${\mathrm{B}}_2$X (X=B, C, N, and O) is carried out, by employing the linearized muffin-tin orbital band method. It is found that the Ni 3d density of states (DOS) in ${\mathrm{YNi}}_2$${\mathrm{B}}_2$C is broader than in fcc Ni metal, and so N(${\mathit{E}}_{\mathit{F}}$) becomes small enough to make the system nonferromagnetic and then superconducting. A rigid-band-like shift of the Fermi level is observed as atom X varies. In the case of ${\mathrm{YNi}}_2$${\mathrm{B}}_2$C, the Fermi level is located right at the van Hove–like singular DOS peak, which originates from saddle-point extremal band crossing Γ. This singular DOS peak at ${\mathit{E}}_{\mathit{F}}$ is expected to be related to the superconductivity observed in ${\mathrm{YNi}}_2$${\mathrm{B}}_2$C. A crude estimate within the framework of the simple rigid-ion approximation indicates that the superconductivity in ${\mathrm{YNi}}_2$${\mathrm{B}}_2$C can be properly described by the conventional phonon mechanism.

The electromagnetic response of a thin type-II superconductor disk of constant thickness d to an applied perpendicular magnetic field is calculated and compared with the response of a thin strip and of bars and cylinders in a longitudinal field. The strip and disk are characterized completely by their sheet resistivity, which may be either nonlinear and static or linear, complex, and frequency dependent. The equations of motion for the sheet current in the strip and disk are derived and discussed. Iterative and numerical-solution methods are presented that account for the infinities of the integral kernel and of the ideal screening current. The linear Ohmic response, realized during flux flow or thermally activated flux flow, is calculated for a jump in the applied field and for an ac field. Simple approximate expressions for the complex ac susceptibilities of an Ohmic strip and disk are given and compared with longitudinal geometry. The penetration of perpendicular flux into an Ohmic strip or disk is not a usual diffusion since a logarithmic infinity of the prpendicular-field component occurs at the edges at all times t and the sheet current always flows over the entire surface. Near the edges, the sheet current has a universal profile, with a maximum which initially penetrates with constant velocity v=0.77D/d and decreases as 1/ √t (D=ρ/${\mathrm{\mu }}_0$, where ρ is the resistivity). At large times t≫${\mathrm{\tau }}_0$ the current and magnetic moment decrease as exp(-t/${\mathrm{\tau }}_0$), where ${\mathrm{\tau }}_0$=0.2492ad/D for a strip with half width a and ${\mathrm{\tau }}_0$=0.1815ad/D for a disk with radius a.

A set of highly sensitive cavity perturbation techniques, quite different from the ones most commonly used to measure thin films, has been developed for measuring the surface impedance of small crystals of high-${\mathit{T}}_{\mathit{c}}$ superconductors. Since the results of these studies differ markedly from most surface-impedance measurements of thin films of high-${\mathit{T}}_{\mathit{c}}$ superconductors, we describe the techniques in detail, including recent improvements. Measurements of the surface resistance and penetration depth of a twin-free crystal of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.95}$ indicate two striking differences from the surface impedance of conventional superconductors. Both quantities exhibit linear temperature dependence at low temperatures rather than the exponentially activated behavior of an s-wave BCS superconductor. Also, a broad peak in the temperature dependence of the surface resistance indicates that the large transport scattering rate in the normal state collapses below ${\mathit{T}}_{\mathit{c}}$ as the holes condense into the superconducting condensate. Systematic studies of the influence of Zn and Ni impurities on the surface impedance indicate that these properties are very sensitive to defects and this sensitivity provides further insight into the pairing state. Although both types of impurities provide strong elastic scattering that limits the collapse of the scattering rate and suppresses the peak in the surface resistance, only Zn has a strong pair-breaking effect. As little as 0.31% Zn substitution makes ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.95}$ gapless, but Ni, which is a magnetic impurity has no such pair-breaking effect up to 0.75% substitution. This difference is the opposite of that expected for an s-wave BCS superconductor.

In this work, the unusual Seebeck effect is taken into consideration in explaining the possible origin of the anomalous Hall effect for high-${\mathit{T}}_{\mathit{c}}$ superconductors. Combining Maki’s theory of transport entropy and Tinkham’s theory of resistive transition, we explain why the anomalous Hall effect can be observed in high-${\mathit{T}}_{\mathit{c}}$ superconductors, but is absent in most conventional superconductors. The behavior of ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$(H,T) in our theory is qualitatively consistent with experiments. In addition, our theory not only predicts that ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ will become positive from ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$<0 when the temperature is decreased in constant magnetic field, but also predicts that ‖${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$‖∝${\mathrm{\rho }}_{\mathit{x}\mathit{x}}^2$ in the region of ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$<0 and that the negative ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ will diminish with increasing defect concentration.

Inelastic neutron scattering has been employed to study in detail the full crystalline-electric-field (CEF) energy-level scheme in the ground-state J multiplet of ${\mathrm{Ho}}^{3+}$ in ${\mathrm{HoBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$ as a function of the oxygen content x. We have been able to resolve ten ground-state transitions for a series of samples covering the superconducting phase as well as the semiconducting one. J mixing and intermediate coupling effects are shown to be necessary to determine unambiguously the nine and five independent CEF parameters of the orthorhombic and tetragonal symmetry, respectively. The large energy shifts and intensity changes of the observed CEF spectra as a function of the oxygen content x are shown to be related predominantly to a charge-transfer process from the chains to the planes, the actual charge transfer being in good agreement with results derived from both bond valence sum considerations for ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$ and similar CEF data for ${\mathrm{ErBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$.

We analyze the spectrum of magnetic excitations as observed by neutron diffraction and NMR experiments in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$, in the framework of the single-band t-t’-J model in which the next-nearest-neighbor hopping term has been introduced in order to fit the shape of the Fermi surface revealed by photoemission. Within the slave-boson approach, we have as well examined the d-wave superconducting state, and the singlet-resonating-valence-bond phase appropriate to describe the normal state of heavily doped systems. Our calculations show a smooth evolution of the spectrum from one phase to the other, with the existence of a spin gap in the frequency dependence of χ’’(Q,ω). The value of the threshold of excitations ${\mathit{E}}_{\mathit{G}}$ is found to increase with doping, while the characteristic temperature scale ${\mathit{T}}_{\mathit{m}}$ at which the spin gap opens exhibits a regular decrease, reaching ${\mathit{T}}_{\mathit{c}}$ only in the overdoped regime. This very atypical combined variation of ${\mathit{E}}_{\mathit{G}}$ and ${\mathit{T}}_{\mathit{m}}$ with doping results from strong-correlation effects in the presence of the realistic band structure considered here. We point out that the presence of a resonance in the spectrum χ’’(Q,ω) is in good agreement with the neutron-diffraction results obtained at x=0.92 and 1.0. This resonance is analyzed as a Kohn anomaly of the second kind in the Cooper channel. Finally, we examine the evolution of the Knight shift and of χ’’(q,ω) at any q, allowing one to study the magnetic correlation length ξ as a function of doping, frequency, and temperature.

Magnetic measurements are carried out on single-crystal ${\mathrm{Y}}_{\mathit{x}}$${\mathrm{Gd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_{2.43}$${\mathrm{Al}}_{0.19}$${\mathrm{O}}_{6+\mathit{y}}$ (x=0,0.5) samples. The magnetic-field dependence of the averaged paramagnetic moments carried by the rare-earth ${\mathrm{Gd}}^{3+}$ ions in these samples is well described by the extended Brillouin function. This paramagnetism tilts the magnetic hysteresis loop and broadens the widths of the magnetic hysteresis ΔM; therefore the magnetization critical-current density ${\mathit{J}}_{\mathit{c}}$ based on the Bean critical-state model deviates from the intrinsic value. At temperature T=4.2 K, this deviation is up to 9% for the single-crystal ${\mathrm{GdBa}}_2$${\mathrm{Cu}}_{2.43}$${\mathrm{Al}}_{0.19}$${\mathrm{O}}_{6+\mathit{y}}$ sample. At the end, the influence of the paramagnetism of ${\mathrm{Gd}}^{3+}$ ions on some other macroscopic magnetic properties is discussed.

Structural, magnetic, calorimetric, and transport studies have been made on a synthesized Tl(1212) system of Tl(${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${)}_2$${\mathrm{PrCu}}_2$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (0≤x≤1). Based on x-ray Rietveld refinement data, the bond length between Pr and oxygen in the adjacent ${\mathrm{CuO}}_2$ layers increases with increasing x, even though the tetragonal lattice parameters decrease with progressive Sr substitution. This may result in a lower degree of hybridization between extended Pr 4f and O 2pπ orbitals and a corresponding reduction of superexchange magnetic coupling strength among Pr moments. Indeed, the anomalously high Néel temperature ${\mathit{T}}_{\mathit{N}}$(Pr) decreases from 8.0–8.2 K for x=0 to 3.6–4.2 K for x=1. The magnetic entropy associated with this antiferromagnetic Pr ordering is estimated from specific-heat data, in which a heavy-fermion-like contribution also prevails.

We have investigated the transient absorption spectra of insulating ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{y}}$ and ${\mathrm{Nd}}_2$${\mathrm{CuO}}_4$ thin films by the pump and probe method from 1.3 to 2.8 eV with a time resolution of 100 fs. For both insulating samples, a bleaching signal with a 0.6–0.9 ps initial decay time was observed in the spectral range of the ${\mathrm{O}}_{2\mathit{p}}$ to ${\mathrm{Cu}}_{3\mathit{d}}$ charge-transfer transition at around 1.8 eV. This initial decay can be explained as a nonradiative transition through the successive emission of magnons having a comparably large energy quantum. In the photon-energy region lower than the bleaching signal, an induced absorption signal is observed. The origin of the induced absorption by pumping pulses has not necessarily been resolved, but the in-gap states induced by the photodoping effect is suggested as a reason.

A strategy to boost the current-carrying capacity of cuprate superconductors beyond the levels attainable with parallel columnar defects was recently proposed. It consists of the enforcement of vortex entanglement by controlled splay of columns. We demonstrate the validity of this suggestion in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_2$ single crystals using the difference in splay naturally occurring in irradiations with two ions differing in mass and energy. The terminal dispersion of the columns produced by 0.58-GeV ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}_{}^{30+}{}_{}{}^{}$ is about 10°, as compared with 1° for 1.08-GeV ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}_{}^{23+}{}_{}{}^{}$. At high temperatures, this large splay results in a persistent current density one order of magnitude larger and a creep rate one order of magnitude smaller.

Electronic-structure calculations, within the local spin density approximation (LSDA), are reported for ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. Significant charge transfer from the Pr ions to both the ${\mathrm{CuO}}_2$ planes and the chains is found relative to ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. This supports hole depletion explanations for the insulating character of ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$. The LSDA electronic structure shows a prominent ‘‘ridge’’ Fermi surface analogous to that in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$, but broader. It is proposed that high-resolution positron measurements of this width may provide a useful test of hole depletion models.

Oxygen isotope effect on Néel temperature (${\mathit{T}}_{\mathit{N}}$) has been studied in the antiferromagnetic cuprates ${\mathrm{La}}_2$${\mathrm{CuO}}_4$, ${\mathrm{Gd}}_2$${\mathrm{CuO}}_4$, ${\mathrm{Gd}}_{1.9}$${\mathrm{Ce}}_{0.1}$${\mathrm{CuO}}_4$, and CuO. For stoichiometric ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ with ${\mathit{T}}_{\mathit{N}}$∼310 K, the Néel temperature of the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ samples is ∼1.8 K lower than the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ samples. For oxygen-annealed ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ samples (in 0.10 and 0.15 bar oxygen partial pressures), the Néel temperatures of the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ samples are ∼3.3–4.7 K lower than the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ samples. For ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ annealed in 0.6 bar oxygen, the Néel temperatures of the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ samples are nearly equal due to segregation into oxygen-rich and oxygen-poor phases. For the other antiferromagnetic cuprates (which lack apical oxygen), we find a negligible oxygen isotope effect on ${\mathit{T}}_{\mathit{N}}$. We suggest that the observed oxygen isotope effect on ${\mathit{T}}_{\mathit{N}}$ of ${\mathrm{La}}_2$${\mathrm{CuO}}_4$ originates from the oxygen-mass dependences of J (in-plane antiferromagnetic exchange energy) due to the nonadiabatic motion of apical oxygen.

We report results of a comparative study of three nonmetals related to the 1-2-3 cuprate superconductors: fully oxygenated ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{y}}$ (PBCO), ${\mathrm{YBa}}_2$${\mathrm{Cu}}_2$${\mathrm{CoO}}_{\mathit{y}}$ (YBCCO), and ${\mathrm{PrBa}}_2$${\mathrm{Cu}}_2$${\mathrm{CoO}}_{\mathit{y}}$ (PBCCO). We measured the resistivity up to 300 K and the absolute thermopower (TEP) up to 400 K. The temperature dependence of the resistivity follows the Mott variable-range-hopping (VRH) law ρ=${\mathrm{\rho }}_0$exp(${\mathit{T}}_0$/T${)}^{1/4}$ in PBCO up to ∼100 K and in the other two systems at least up to room temperature. The results of the TEP measurements show that in YBCCO and in PBCCO the VRH probably takes place via energy states lying mainly below the chemical potential, while in PBCO this process utilizes states lying symmetrically on both sides of the chemical potential. In PBCO the TEP exhibits a cusp at low temperatures that is probably associated with the Néel point of the Pr sublattice. In PBCCO we found at low temperatures a sharp sign reversal of the TEP, from p type at high temperatures to n type at low temperatures, which needs further investigation.

The magnetic behavior of the 71-K superconductor ${\mathrm{Tl}}_{0.5}$${\mathrm{Pb}}_{0.5}$${\mathrm{Sr}}_4$${\mathrm{Cu}}_2$${\mathrm{CO}}_3$${\mathrm{O}}_7$, which consists of an intergrowth of the two nonsuperconducting phases ${\mathrm{Sr}}_2$${\mathrm{CuO}}_2$${\mathrm{CO}}_3$ and ${\mathrm{Tl}}_{0.5}$${\mathrm{Pb}}_{0.5}$${\mathrm{Sr}}_2$${\mathrm{CuO}}_5$, has been studied. Its pinning properties in terms of the critical current density ${\mathit{J}}_{\mathit{c}}$ and the irreversibility line have been established using a modified-Bean-model expression for the magnetization data and compared to results for other thallium cuprates. Typical ${\mathit{J}}_{\mathit{c}}$ was calculated to be ∼8×${10}^6$ A/${\mathrm{cm}}^2$ at 5 K in a field of 0.2 T. The analysis of the reversible magnetization, leading to basic values of the parameters for this oxycarbonate as ${\lambda }_{\mathit{a}\mathit{b}}$(0)=170 nm, ${\xi }_{\mathit{a}\mathit{b}}$(0)=2.39 nm and κ=72.5, was also performed. The latter values are compared to other existing data especially those concerning the thallium-based superconductors which have been derived from similar analyses. This study shows that the superconducting behavior of this oxycarbonate is closer to multiple copper layered cuprates than to the single copper layer ‘‘1201’’ phase although carbonate groups connect two successive copper layers. It can be considered as intermediate between the thallium bilayer cuprates and the best lead-doped ‘‘1223’’ and ‘‘1212’’ superconductors.

We present here a study of the thermodynamic properties of high-${\mathit{T}}_{\mathit{c}}$ oxide superconductors using our formulation based on the hole-pairing model. We extend our earlier formulation by including the effects of intersite Coulomb repulsion (${\mathit{X}}_{\mathit{i}\mathit{j}}$) between holes and assess the new features that can be added to our earlier results. We analyze the stability of the superconducting state in the presence of such a repulsive interaction and note the qualitative and quantitative changes in the results for parameter ranges for which high ${\mathit{T}}_{\mathit{c}}$ occurs in our model. An analytical expression for ${\mathit{T}}_{\mathit{c}}$ is derived which can be used in qualitative studies of ${\mathit{T}}_{\mathit{c}}$ versus n. We calculate the temperature dependence of the gap function and electronic heat capacity and compare our theoretical results with available experimental results.