The linear ac susceptibility in a transverse magnetic ac field is calculated for thin strips and disks with arbitrary complex resistivity ${\mathrm{\rho }}_{\mathrm{ac}}$(ω). The exact result is approximated with high precision by a finite sum. This analytic expression allows one to extract ${\mathrm{\rho }}_{\mathrm{ac}}$(ω) from contact-free magnetic measurements on high-${\mathit{T}}_{\mathit{c}}$ superconductors in search for scaling laws and phase transitions. As an example the susceptibility of a superconducting disk with pinning and thermally assisted flux flow is given.

The phase shift as a key concept to understand the Luttinger liquid behavior in one dimension is explored in the strong-coupling regime of the Hubbard model, where a simple charge-spin separation picture exists. We demonstrate an explicit connection between the phase shift upon doping and the Marshall sign hidden in the spin background. The obtained many-body phase-shift field reproduces the known non-Fermi-liquid behavior where the phase-shift effect also plays a crucial role to shift the Fermi surface to satisfy the Luttinger volume. The connection of the phase shift and the fractional statistics transformation is also discussed.

We have investigated the effect of pressure (up to 14 GPa) on the coupling between a ${\mathrm{Nd}}^{3+}$ crystal-field excitation and a ${\mathrm{CuO}}_2$-plane oxygen phonon near 300 ${\mathrm{cm}}^{\mathrm{-}1}$ in the two high-temperature superconductors ${\mathrm{NdBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ and ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$${\mathrm{NdCu}}_3$${\mathrm{O}}_8$. Raman spectra of single crystals as well as ceramic samples with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ isotopes were measured at different temperatures (10–300 K). From the low-temperature pressure shift of the coupled phonon-crystal-field doublet we deduce the pressure coefficients for the bare crystal-field excitation energy and the phonon-crystal-field coupling constant, both of which increase with increasing pressure. For ${\mathrm{NdBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ the experimental results are compared to a point-charge model calculation of the pressure dependence of the crystal-field levels and coupling constant.

Using a vibrating-reed technique, we studied the flux penetration in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals in the strong pinning regime well below the irreversibility line. The resonant frequency and damping of the vibrating superconductor are dramatically enhanced by the nonuniform and hysteretical penetration of the flux lines at low temperature. Using a critical-state model, we determine the critical current density ${\mathit{J}}_{\mathit{c}}$ to be about 3.5×${10}^6$ A/${\mathrm{cm}}^2$ at 4.2 K. We also found that ${\mathit{J}}_{\mathit{c}}$ obeys an exponential temperature dependence and the flux creep at low temperature can be characterized by a low activation energy barrier on the order of 20 K.

The dissipation process in transport-current-carrying ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ samples with preferential grain orientation in zero applied magnetic field and close to the mean-field critical temperature ${\mathit{T}}_{\mathit{c}0}$ was investigated. The ${\mathit{T}}_{\mathit{c}0}$ value was obtained from an analysis of the fluctuation-induced excess dc conductivity in the framework of the Aslamazov-Larkin theory of paraconductibility. The measured transport critical-current density, which, at least at high temperatures, is essentially given by the contribution of good superconducting intergrain contacts in the sample, has a relatively large component decreasing linearly with temperature and vanishing clearly below ${\mathit{T}}_{\mathit{c}0}$. The temperature dependence of the transport critical current as well as the form of the current-voltage characteristics at low voltages can be understood by considering a current-dependent vortex-antivortex unbinding, size limited at the intergranular contacts, and by taking into account the contribution of entropy to the unbinding process.

By measuring the magnetic torque moment in the field-sweeping process, the temperature and field dependence of the width of the irreversible magnetic moment (ΔM) and the normalized relaxation rate (Q=d lnj/d lnE) of a ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ thin film were obtained. With Δ${\mathit{M}}_{\min }$≊2.5×${10}^{\mathrm{-}5}$ emu as the criterion, the irreversibility lines at different sweeping rates were determined. It was found that at ${\mathit{T}}_{\mathrm{irr}}$ and ${\mathit{B}}_{\mathrm{irr}}$, E∝j, and ${\mathit{B}}_{\mathrm{irr}}^{\mathrm{-}1/2}$ is linearly related to ln(dB/dt), which can only be explained by the thermally assisted flux flow model. Further investigation shows that, at irreversible temperature and field, ${\mathit{U}}_{\mathit{c}}$ is much smaller than ${\mathit{k}}_{\mathit{B}}$T, which indicates that the depinning of vortices induced by strong thermal activation is probably the origin of the irreversibility line.

The critical properties of the diluted Potts model on diamond-type hierarchical lattices of different fractal dimensions were studied recently by Wu et al. [Phys. Rev. B 48, 3171 (1993)]. Although the aim of the paper is very interesting, we show in this comment that the fixed bimodal bond-probability distribution used in their renormalization-group work is not appropriate to deal with this disordered model. Such treatment violates the Harris criterion and may lead to spurious results. We point out that the correct way to deal with randomness is to rescale the full distribution and take its second moment as an additional parameter. We use this method and find that the critical properties are different from those which Wu et al. predicted.

First-order Raman scattering in natural and ${}_{}{}^{13}{}_{}{}^{}\mathrm{enriched}$ diamond was measured at high pressures up to 15 GPa in a diamond anvil cell. The ratio ${}_{}{}^{12}{}_{}{}^{}\nu$${/}^{13}$ν, where ν is the frequency of the first-order Raman line, decreases with pressure. The deviation of the frequency ratio from the limiting classical value of ${(}^{13}$m${/}^{12}$m${)}^{0.5}$=1.0408, where m is the isotopic mass, becomes stronger at high density. This kind of behavior means that the quantum contribution to the physical properties of diamond increases with density. This is typical of systems with Coulomb interaction, e.g., metals and high-density plasma.

We present the results of an inelastic neutron-scattering investigation of the crystal-field potential of ${\mathrm{PrCu}}_2$${\mathrm{Si}}_2$. The crystal-field parameters and corresponding level scheme have been determined from a profile refinement of the neutron spectra in the paramagnetic state. The overall splitting is 11.33 meV with a doublet ground state and the first excited singlet at 1.35 meV. The low-energy transitions produce a Schottky contribution to the specific heat that agrees well with the measurements above the Néel temperature. Therefore the specific heat does not provide evidence for heavy-fermion behavior as previously proposed.

We have measured the low-temperature nonlinear conductivity in the spin-density-wave state of (TMTSF${)}_2$X alloys. We find that an expression of σ(E)=${\mathrm{\sigma }}_{0\mathit{E}}$exp(-${\mathit{E}}_0$/E), suggestive of a tunneling process, describes the nonlinear conduction with the characteristic field ${\mathit{E}}_0$ increasing with increasing disorder while ${\mathrm{\sigma }}_{0\mathit{E}}$ is independent of the impurity concentration within experimental error. We also discuss the implications of our findings.

We present an interesting connection between Brownian motion and magnetism. We use this to determine the distribution of areas enclosed by the path of a particle diffusing on a sphere. In addition, we find a bound on the free energy of an arbitrary system of spinless bosons in a magnetic field. The work presented here is expected to shed light on polymer entanglement, depolarized light scattering, and magnetic behavior of spinless bosons.

We study dynamic responses of two-dimensional arrays of ideal Josephson junctions at zero temperature. In the appropriate limit the dc component of the applied current is shown to be quantized, which is a generalization of the Bloch oscillation previously considered in a single Josephson junction. The vortex description manifests the topological character of the quantization. The possibility of fractional quantization associated with the ground-state degeneracy is also pointed out. This together with the giant Shapiro steps and the quantum Hall effect suggests the three types of topological quantization present in the system.

The synthesis and results of electrical-resistivity (1.5–300 K), ac-magnetic-susceptibility (1.5–5 K), and specific-heat (1.7–30 K) measurements are reported on a ternary rare-earth–nickel-silicide compound ${\mathrm{Lu}}_2$${\mathrm{Ni}}_3$${\mathrm{Si}}_5$. The compound is found to be superconducting below 2.1 K. The magnetic-susceptibility measurements show the onset of diamagnetism at 2.1 K and the resistivity goes to zero at 2.0 K with the same onset temperature. The resistivity above the transition temperature shows a metallic behavior. A deviation from linear resistivity at high temperatures implies a short mean free path. The heat capacity shows a jump with a peak at 1.9 K, which indicates bulk superconducting ordering in this sample. The estimated value for γ(=${\mathit{C}}_{\mathit{p}}$/T as T→0) is 5.8 mJ/Lu ${\mathrm{molK}}^2$ and Δ${\mathit{C}}_{\mathit{p}}$/γ${\mathit{T}}_{\mathit{c}}$ is 1.1, which is lower than the BCS value of 1.43. From these results, we conclude that ${\mathrm{Lu}}_2$${\mathrm{Ni}}_3$${\mathrm{Si}}_5$ is a weak-coupling BCS superconductor.

The structure of a vortex line in a ${\mathit{d}}_{{\mathit{x}}^2\mathrm{-}{\mathit{y}}^2}$ superconductor is calculated self-consistently in the framework of the Bogoliubov–de Gennes theory. The inner core of the vortex containing localized quasiparticle excitations is found to be separated from the asymptotic pure d-wave state by a region where low-lying fermionic excitations are absent. A domain structure of the relative phase of the s-wave and d-wave components is identified. The results are interpreted in terms of a Ginzburg-Landau theory.

It is demonstrated that the spatial decay of the pair propagator in a Luttinger liquid with spin-charge separation contains a logarithmic correction relative to the free-Fermi-gas result in a finite interval between the spin and charge thermal lengths. It is argued that similar effects can be expected in higher-dimensional systems with spin-charge separation and that the temperature dependence of the upper critical field ${\mathit{H}}_{\mathit{c}2}$ curve is a probe of this effect.

We have measured the upper and lower critical fields of superconducting ${\mathrm{Ba}}_6$${\mathrm{C}}_{60}$. Near ${\mathit{T}}_{\mathit{c}}$, from the slope of the measured upper critical field, ${\mathit{dH}}_{\mathit{c}2}$/dT=0.45 T/K, we obtain the zero-temperature Ginzburg-Landau coherence length as ${\xi }_{\mathrm{GL}}$=120 Å. Using the lower critical-field data, the penetration depth at T=0 is estimated to be λ(0)=1800 Å. Combining λ(0) with the value of ${\xi }_{\mathrm{GL}}$, we estimate the Fermi energy ${\mathit{E}}_{\mathit{F}}$ to be =0.15 eV. Thus, in comparison with the alkali-metal-doped fullerenes, the superconducting parameters ${\mathit{H}}_{\mathit{c}2}$, ${\xi }_{\mathrm{GL}}$, and the resulting Ginzburg-Landau parameter κ, are significantly different in the case of the superconducting Ba-doped fullerene.

We have determined the temperature dependence of the ab-plane penetration depth ${\lambda }_{\mathit{ab}}$ in epitaxial ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ films by measuring the magnetic-field dependence of the critical current of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ bicrystal grain-boundary Josephson junctions. Using this dc technique the change of the penetration depth with varying temperature has been measured between 4.2 and 60 K with a resolution of 0.2 Å. We found a linear ${\lambda }_{\mathit{ab}}$(T) dependence at temperatures below about 10 K. This linear dependence is consistent with lines nodes of the gap function.

We report evidence from c-axis-polarized Raman scattering and optical-reflectivity measurements that doping-induced and phonon-mediated changes in the O(4)-Cu(1)-O(4) structure influence c-axis charge dynamics in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathit{x}}$. With increased doping, we observe a rapid increase in the interbilayer hopping rate which we suggest may be caused by the systematic decrease in the Cu(2)-O(4) bond length. Also, c-axis-polarized Raman scattering measurements provide evidence that dynamical modulation of the O(4)-Cu(2) bond length by c-axis phonons contributes to ‘‘assisted’’ interbilayer hopping.

Using a quantum Monte Carlo technique combined with the method of maximum entropy, we calculated the magnetic susceptibility and spectral properties of the degenerate single-impurity Anderson model in the presence of spin-orbit and crystal-field splitting. At small hybridization and moderate temperatures, the magnetic susceptibility displays a nonuniversal behavior. Under the influence of spin-orbit splitting, the magnetic susceptibility decreases due to the quenching of a sixfold-degenerate state to an effectively doubly degenerate state. The effect of crystal-field splitting on the magnetic susceptibility is less pronounced. The temperature dependence of the spectral function changes dramatically under the influence of spin-orbit splitting. In the accessible temperature regime, the central peak at ω∼0 decreases with decreasing temperature.

The electronic structure of a ${\mathrm{Bi}}_2$${\mathrm{CuO}}_4$ single crystal is investigated by x-ray photoelectron (XPS), x-ray Auger-electron (XAES), and electron-energy-loss (EELS) spectroscopies. The analysis of the XPS and XAES data confirms that ${\mathrm{Bi}}_2$${\mathrm{CuO}}_4$ is a charge-transfer insulator with a band gap of about 2 eV, while the Cu-O bond in ${\mathrm{Bi}}_2$${\mathrm{CuO}}_4$ is more ionic than in CuO and the ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_{8-\delta }$ superconductor. Furthermore, the density of the empty states is tentatively described from a combined analysis of the EELS and XPS data and some electronic transitions are identified from the EELS spectra.