The structure of edge states in general finite antiferromagnetic quantum spin chains with arbitrary spin value S is discussed within the framework of the nonlinear-sigma model (NLσM) plus a topological θ term. Based on a large-N theory of SU(N) quantum antiferromagnets and strong-coupling expansion, we argue that edge states with fractionalized spin quantum number S’ exist in all spin chains with S≥1, with S’=S/2 for integer spin chains and S’=(S-1/2)/2 for half-integer spin chains.

We study a one-dimensional quantum Hamiltonian which is related to a highly anisotropic version of the two-dimensional Ashkin-Teller model. We explore the parameter region and complete its ground-state phase diagram. This problem is studied by using duality relations and by series expansions up to seventeenth order. Corresponding critical indices are also calculated. In this parameter region, a line of continuously varying critical indices is found.

We present the possibility that the order parameter describing the 17.5-K magnetic transition of ${\mathrm{URu}}_2$${\mathrm{Si}}_2$ has the same symmetry as, and couples weakly to the antiferromagnetic magnetic dipole order parameter. We also present triple-spin correlators that exhibit the correct symmetry properties to describe this transition.

The magnetic-field distribution of vortices in single-crystal Nb thin foil specimens has been quantitatively measured with high spatial resolution by electron holography using a 300-kV field-emission transmission electron microscope. The diameters of single vortices were observed to broaden with increasing temperature under constant applied magnetic field. Vortex diameters varied from ∼150 nm at 4.5 K to ∼230 nm at 8 K, in agreement with the expected behavior. While vortices broadened with temperature, the total flux enclosed by them was constant.

A heuristic model of flux flow and vortex cutting that does not imply a buildup of longitudinal flux is given for type-II superconducting cylinders carrying a current in the presence of an axial magnetic field.

Phase diagram of the extended Hubbard model with on-site repulsion and nearest-neighbor attraction is obtained for various band fillings, covering the strong-correlation regime, in one dimension by mapping the system to the Tomonaga-Luttinger model with use of exact diagonalization of finite systems. We find that the strong electron correlation makes the superconducting region, which is sandwiched between spin-density wave and phase-separation regions, significantly wider than expected from the weak-coupling g-ology.

Pinning of interactive quantized vortices has been studied by numerical simulation. A hemispherical pinning site whose radius is much larger than the vortex core size has a finite capacity; it can pin only less than five vortices because of the interaction between vortices. The critical depinning velocity for pinned vortices is discussed.

We consider the influence of planar ‘‘magnetic’’ imperfections which destroy the local magnetic order, such as Zn impurities or ${\mathrm{Cu}}^{2+}$ vacancies, on the low-temperature properties of the cuprate superconductors. In the unitary limit, at low temperatures, for a ${\mathit{d}}_{{\mathit{x}}^2\mathrm{-}{\mathit{y}}^2}$ pairing state such imperfections produce low-energy quasiparticles with an anistropic spectrum in the vicinity of the nodes. We find that for the ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ system, one is in the quasi-one-dimensional regime of quasiparticle scattering, discussed recently by Altshuler, Balatsky, and Rosengren, for impurity concentrations in excess of ∼0.16% whereas Ya-Ba-Cu-${\mathrm{O}}_7$ appears likely to be in the true two-dimensional scattering regime for Zn concentrations less than 1.6%. We show the neutron-scattering results of Mason et al. [Phys. Rev. Lett. 71, 919 (1993)] on ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.14}$${\mathrm{CuO}}_4$ provide strong evidence for ‘‘dirty d-wave’’ superconductivity in their samples. We obtain simple expressions for the dynamic spin susceptibility and ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ spin-lattice relaxation time, ${}_{}{}^{63}{}_{}{}^{}$${\mathit{T}}_1$, in the superconducting state.

The results of polarized micro-Raman scattering experiments on ${\mathrm{YBa}}_2$${\mathrm{Fe}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$ with δ=0.1 are reported. We identified seven out of the total ten by symmetry Raman-allowed phonons at 134 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{A}}_{1\mathit{g}}$), 148 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{E}}_{\mathit{g}}$), 219 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{A}}_{1\mathit{g}}$), 300 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{B}}_{1\mathit{g}}$), 478 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{A}}_{1\mathit{g}}$), 493 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{E}}_{\mathit{g}}$), and 691 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{A}}_{1\mathit{g}}$). The Raman-active phonons are assigned to definite atomic vibrations in close comparison with the structurally similar ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$, usually simple considerations based on charge and bond length.

The tetragonal-orthorhombic improper ferroelastic phase transition and domain formation of the order-disorder KSCN model is studied by molecular-dynamics simulation. A two-dimensional model of either 105×105 or 49×49 unit cells represents a layer of this crystal. The simulation determines the orientational and strain order parameters and transition temperature. The mean-field theory gives excellent qualitative agreement of the calculated and simulated phase transition temperature. On quenching from the disorder phase and subsequent annealing, a tweed texture is obtained, which later evolves to a stripe phase with well oriented ferroelastic domain walls and arbitrarily oriented antiphase boundaries.

Using angle-resolved photoemission, we observed a nonzero superconducting gap and the presence of a superconducting condensate along all three major symmetry directions. We find that the gap is highly anisotropic, with a gap as small as 1–2 meV along Γ-Y, 4–8 meV along Γ-X, and 14–20 meV along Γ-M. We argue that our data imply either an anisotropic s-wave order parameter or an unconventional, two-component order parameter, and that measuring the size of the gap does not by itself distinguish between the two possibilities. We propose a phenomenological unconventional order parameter, and note the quantitative agreement between theory and experiment.

It is known that ${\mathrm{Ca}}^{2+}$ substitution at the ${\mathrm{Y}}^{3+}$ site reduces the superconducting transition temperature (${\mathit{T}}_{\mathit{c}}$) of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ (Y-123) when y≃0 [Phys. Rev. B 49, 6385 (1994)]. On the other hand, in the y≃1 sample, which is nonsuperconducting, 20 at.% Ca at the Y site makes the sample superconducting [J. Solid State Chem. 78, 192 (1989)]. We have prepared oxygen-deficient samples of the series ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ by annealing them in flowing Ar atmosphere at 400 °C. We find that substitution of divalent Ca at the trivalent Y site enhances the superconducting critical temperature ${\mathit{T}}_{\mathit{c}}$ of the oxygen-deficient Y-123. From x-ray-diffraction studies, it is observed that the cause of such a contrasting behavior of Ca substitution is the existence of divalent Ca in two different coordination numbers in the discussed system. In the oxygen-deficient Y-123, Ca exists in eightfold coordination while in the fully oxygenated Y-123, it is sixfold coordinated. It is argued that in these compounds the coordination number of Ca is dependent on the oxygen content and the concentration of doped Ca in the material.

Helium-bubble growth in α-implanted palladium has been investigated by positron-lifetime measurements as a function of isothermal annealing time, t. The bubble radius shows first an expected ${\mathit{t}}^{1/6}$ variation and then an anomalous time dependence faster than ${\mathit{t}}^1$. It is shown that a model based on surface-diffusion-controlled migration and coalescence, taking into account the dependence of bubble diffusivity on the time-varying helium density in the bubble and ledge nucleation, explains the observed behavior.

Measurements of the complex dielectric permittivity in nominally pure ${\mathrm{SrTiO}}_3$ are reported for frequencies ${10}^{\mathrm{-}3}$ Hz≤ν≤${10}^8$ Hz and temperatures 0.1 K≤T≤300 K. The experiments reveal relaxation phenomena similar to those reported from elastic measurements. The onset of constant loss below 50 K and a low-temperature relaxation reveals characteristic features of a tunneling motion. These phenomena can be interpreted to be characteristic of a quantum phase transition into a coherent quantum state.

Brillouin-light-scattering measurements have been performed on both bulk and thin supported polybutadiene (PB) films, in the frequency range 1–300 GHz. The results obtained on the relaxation behavior of PB have been interpreted in the framework of the mode-coupling theory and compared with neutron spin-echo data relative to the same system. For temperatures higher than the critical temperature ${\mathit{T}}_{\mathit{c}}$, a quantitative agreement of the mean relaxation time with the viscosity time scale has been found, together with the validity of a time-temperature scaling law. For temperatures approaching the glass transition, a departure of relaxation time from the viscosity time scale has been observed. This phenomenon has been attributed to a decoupling between structural and secondary relaxation processes.

To obtain a better insight into the nature of valence states of Sm ${\mathrm{ionsinSmRuSn}}_3$ and to verify the differing conclusions reached by T. Fukuhara, I. Sakamoto, and H. Sato [J. Phys. Condens. Matter 3, 8917 (1991)] and C. Godart et al. [Phys. Rev. B 48, 16 402 (1993)], we have systematically analyzed the magnetic-susceptibility data by considering the effects of crystalline electric field, exchange interaction, and valence fluctuation. In this compound, Sm ions occupy two different sites, 6d and 2a, in the ratio of 3:1. Our analysis shows that Sm ions at the 6d site are in a trivalent state and those at the 2a sites are in a valence fluctuating state. This supports the claim made by C. Godart et al. [Phys. Rev. B 48, 16 402 (1993)].

A Luttinger-liquid fixed point is obtained in the strong-coupling limit of the one-dimensional Kondo-lattice model with a frustrating next-nearest-neighbor hopping. The Luttinger-liquid phase has a large Fermi surface whose area is determined by the total number of conduction electrons and localized spins. A numerical study for finite systems shows that the paramagnetic ground state of the finite Kondo lattice model away from half-filling is adiabatically connected with this fixed point.

We show that the forbidden components of the 14.4-keV transition in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ have radio-frequency sidebands of nonvanishing intensity, and point out that lines having the position and intensity predicted in this work can be identified in the Mössbauer spectra of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclei in Permalloy, reported by Tittonen et al., Phys. Rev. Lett. 69, 2815 (1992). The presence of sidebands to the forbidden hyperfine transitions of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ proves that nuclear multiphoton transitions are taking place in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclei subjected to radio-frequency magnetic fields.

Muon-spin-rotation experiments have been carried out in single crystals of the heavy-fermion compound ${\mathrm{CeRu}}_2$${\mathrm{Si}}_2$. The muon-stopping site has been determined from an analysis of the muon Knight shift. The zero-field relaxation rate of the muon polarization exhibits a small but significant increase below ∼2 K which can be suppressed in longitudinal-field experiments. This result provides definite evidence for the occurrence of static electronic magnetism involving ultrasmall moments of the order of ${10}^{\mathrm{-}3}$${\mathrm{\mu }}_{\mathit{B}}$.

Measurements of resistivity ρ, thermopower S, and magnetic susceptibility χ are reported on single-crystal CeRhSb. Only along the orthorhombic a axis, χ(T) exhibits a pronounced peak at 13 K and ρ(T) has a shoulder at around 20 K. These anomalies and the relations ${\mathrm{\rho }}_{\mathit{c}}$≳${\mathrm{\rho }}_{\mathit{b}}$≳${\mathrm{\rho }}_{\mathit{a}}$ and ${\mathrm{\chi }}_{\mathit{a}}$≳${\mathrm{\chi }}_{\mathit{b}}$≳${\mathrm{\chi }}_{\mathit{c}}$ resemble those in the isostructural Kondo semiconductor CeNiSn. However, the anisotropy in ρ(T), χ(T), and S(T) is still weaker than that in CeNiSn. The magnetic contribution to the specific heat divided by temperature ${\mathit{C}}_{\mathit{m}}$/T reveals a maximum of 0.1 J/${\mathrm{K}}^2$ mol near 10 K and decreases linearly with decreasing temperature. These results indicate that the gap formation in CeRhSb and CeNiSn originates from a similar type of hybridization of 4f states with a conduction state.