Features of an incommensurate-to-commensurate transition in barium sodium niobate, which is obtained in a cooling process from a tetragonal phase, have been theoretically examined on the basis of the Ginzburg-Landau theory. The present theory which takes into account the contribution of higher-order distortion waves produced from higher-order harmonics via the umklapp process, well reproduces an experimentally obtained change in an incommensurability δ on cooling. The theory also predicts both a discommensuration with a phase slip of 2π/4 and the incommensurate-to-commensurate transition.

We present scanning force microscope images of craterlike defects induced by individual 78.2-MeV ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ ions incident on organic single-crystal L-valine surfaces. For grazing incidence ions, the craters are elongated along the ion azimuth of incidence and display a raised tail in the surface above the ion track. This permanent plastic deformation of the surface indicates that a hydrodynamic pressure-pulse phenomenon occurs in response to the electronically deposited energy.

Nuclear-spin relaxation (NSR) and electrical conductivity observed in various inorganic oxide glasses at low temperatures are found to be related by the fluctuation-dissipation theorem, indicating a common physical origin of the relaxation mechanism due to fluctuating charges. However, in heavy-metal fluoride glasses NSR is shown to detect additional fluctuations which are not observed by counductivity experiments. The underlying relaxation process is caused by magnetic fluctuations without any accompanying charge motions.

We have succeeded in growing large-size fractals (∼2–3 cm) in solution-casted ion-conducting polymer films of polyethylene oxide doped with ammonium iodide. These are shown to be ‘‘diffusion-limited aggregates’’ due to iodine ions in random walk. This mechanism is supported by energy dispersive x-ray analysis, x-ray diffraction, optical absorption, polarization, and complex impedance studies.

The low-field phase boundaries of bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at V=24.18 ${\mathrm{cm}}^3$/mole were determined from isochoric pressure measurements. We clarified that the critical magnetic field ${\mathit{B}}_{\mathit{N}}$ of the transition line between the low-field and the paramagnetic phases was described as ${\mathit{B}}_{\mathit{N}}$∼ √${\mathit{T}}_{\mathit{N}}$(0)-${\mathit{T}}_{\mathit{N}}$(${\mathit{B}}_{\mathit{N}}$) as a function of the critical temperature ${\mathit{T}}_{\mathit{N}}$. The sharp kink at the triple point along the low-field phase boundary indicates that the transition between the high-field and paramagnetic phases is first order near the triple point.

The possibility of macroscopic mass transfer in an ionic crystal placed in a high-frequency electric field has been studied theoretically. The plastic deformation of the crystal is shown to take place due to the vacancy-drift perturbations caused by space-charge formation in the near-surface layer and by surface permeability asymmetry with respect to the direction of the motion of atoms through it. The estimates prove that the effects considered can be essential in technological processes, e.g., in microwave sintering of ceramics.

From low-temperature heat capacity and ac susceptibility data it is inferred that YbNiSb orders magnetically at 0.8 K. An unusually large magnetic-field dependence of the heat capacity measured up to 20 K, and also a large decrease in the electrical resistivity (∼1200 μΩ cm) below 150 K are observed. These data suggest an appreciable dynamical mass renormalization of the quasiparticles due to a 4f conduction-band mixing effect.

The chlorine-NQR and the deuteron-NMR relaxation have been investigated in (${\mathrm{ND}}_{\mathit{x}}$${\mathrm{H}}_{4\mathrm{-}\mathit{x}}$${)}_2$${\mathrm{SnCl}}_6$ (x=0,0.4) in the temperature range 4–300 K. Besides the large cross-relaxation maximum observed in both natural and partially deuterated compounds at about 55 K the ${}_{}{}^{35}{}_{}{}^{}\mathrm{NQR}$ relaxation rate shows two smaller maxima at 20 and 30 K in the deuterated salt only. These maxima are shifted to a higher temperature for ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ isotope. The peak at 30 K has a corresponding tunneling channel in the ${}_{}{}^2{}_{}{}^{}\mathrm{NMR}$ relaxation rate. Deuteron spin-lattice relaxation rates, measured at 13.86 and 52.37 MHz, besides the level-crossing maxima, also show classical maxima related to molecular motions against a barrier about 15% of the full potential. All these effects are caused by limited jumps in a substructure at the bottom of the potential.

An exact solution for the statistical mechanics of a one-dimensional ferromagnetic chain with an impurity under an external magnetic field is obtained by the transfer-matrix method and the results are compared with that of a pure chain without an impurity. Expressions for the free energy and susceptibility are obtained in closed form. The mechanisms of the change of phase variation of the wave vector and correlation length are demonstrated graphically.

We propose a numerical technique, the forced-oscillator method, to investigate finite-temperature properties of quantum spin systems. The space and time complexity of this method are linear in the matrix dimension, which should be compared with the square or quadratic dependence of conventional methods. We apply this method to calculations of the specific heat of the spin-1/2 quantum Heisenberg antiferromagnet on the kagome$iaa— lattice. We find only a single-peak in contrast to a double-peak structure claimed in the literature.

The temperature dependence of the thermoelectric power S(T) of single crystals of alkali-metal-doped fullerenes is linear from 300 to 100 K, but exhibits a shoulder above the superconducting transition temperature. This behavior is discussed in terms of the electron-phonon interaction. While the possibility of phonon drag is not excluded, it is shown that the low-temperature behavior is consistent with electron-phonon mass-enhancement effects if it is assumed that the electrons are coupled strongly to low-frequency interball or ball–alkali-metal-atom phonons.

We present measurements of the magnetic torque acting upon a single crystal of ${\mathrm{UBe}}_{13}$, measurements made with a capacitive magnetometer. We observe pronounced magnetic oscillations in the torque resulting from the de Haas–van Alphen effect. A conventional analysis reveals that these oscillations result from ‘‘light fermions’’ with an effective mass ${\mathit{m}}^{\mathrm{*}}$=0.017${\mathit{m}}_{\mathit{e}}$ (${\mathit{m}}_{\mathit{e}}$ is the bare electron mass). The Fermi surface associated with these light quasiparticles is anisotropic. We present arguments that these oscillations represent an intrinsic phenomenon and compare our results with those of other groups.

We discuss a general procedure to map a quasi-two-dimensional vortex gas to a layered sine-Gordon (SG) Hamiltonian. The latter is amenable to renormalization-group (RG) treatment by standard methods. The formalism is discussed in the context of recent work on the critical behavior of high-temperature superconductors at zero field. The method is illustrated with reference to the applicability of a layered SG model for which a RG analysis has been performed.

Calculations based on the standard equations for the flow He II in tubes predict large pressure and moderate temperature maxima when the tube is long and narrow. This effect has not, to our knowledge, been previously observed. Experimental data are presented that confirm the existence of the pressure maxima in capillaries of diameter 0.3 μm. The measured data are in good agreement with predictions. The data validate the model equations for flow in capillaries and porous media using the bulk value of the Gorter-Mellink parameter. This effect may impact interpretations of experimental searches for size effects.

Anyon superfluidity is studied by using nonrelativistic currents and densities as coordinates. The excitation spectrum, obtained by solving the equation of motion of a suitably constructed excitation operator, reveals the importance of vortex-type excitations and predicts an anomalous phonon dispersion in the long-wavelength limit.

We present experimental results on electrical measurements of evaporated thin lead films (inverse swiss cheese model) and ion-milled thin films (swiss cheese model) at liquid-helium temperatures near the superconductor-insulator percolation threshold. We provide evidence for the nonuniversality of the critical exponents for the critical current in two dimensions for the two systems studied, in good agreement with theoretical results.

The specific heat and susceptibility data for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on Grafoil are analyzed in the framework of the Landau Fermi-liquid theory. The data suggest that the dominant interaction between ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ quasiparticles is an attraction in the p-wave channel. We have calculated explicitly the superfluid transition temperature in a two-dimensional Fermi gas and found that the prefactor in ${\mathit{T}}_{\mathit{c}}$ is very small (∼${10}^{\mathrm{-}2}$–${10}^{\mathrm{-}3}$ depending on the form of the potential). For moderate areal densities of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${\mathit{T}}_{\mathit{c}}$ is estimated to be on the scale of several millikelvin. The relevance of these results to the change in the temperature behavior of the specific heat observed below ${\mathit{T}}_{\mathit{k}}$=3.2 mK is discussed.

Analysis of anisotropic transport data of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ shows that the out-of-plane resistivity ${\mathrm{\rho }}_{\mathit{c}}$ changes from nonmetallic to metallic following a reduction in ${\mathrm{\rho }}_{\mathit{c}}$. The metallic ${\mathrm{\rho }}_{\mathit{c}}$ arises from a conventional relaxation mechanism within the framework of the band theory, while the nonmetallic ${\mathrm{\rho }}_{\mathit{c}}$ is dominated by hopping conduction. Whether the Mott-Ioffe-Regel rule is satisfied by the out-of-plane transport draws a distinction between relaxation transport and hopping conduction. The results can account for experimental data observed on single-crystal ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ as well as other high-${\mathit{T}}_{\mathit{c}}$ copper oxides.

Mössbauer spectroscopy of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_{3\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{O}}_{6+\mathit{y}}$ for x=0.09 was used to study the site distribution of Fe in oxygen-rich and oxygen-reduced samples. In the superconducting sample (y=1) (${\mathit{T}}_{\mathit{c}}$=85 K) more than 90% of the Fe resides in the Cu(1) site. For y=0 the Cu(2) site orders magnetically at ${\mathit{T}}_{\mathit{N}}$=425 K. Based on the typical behavior of Fe in the magnetic Cu(2) site, we find that about 80% of the Fe occupies this site, thus we prove migration of Fe from Cu(1) to Cu(2) sites during depletion of oxygen at elevated temperatures. The spectrum above ${\mathit{T}}_{\mathit{N}}$ is smeared because of a distribution in the quadrupole interactions.

The local geometry, energy stabilization, and pseudolocal ${\mathit{t}}_{1\mathit{u}}$ vibration mode of the ${\mathrm{Cu}}^{+}$ impurity in the alkali halide crystals have been investigated with the ab initio perturbed ion cluster-in-the-lattice methodology. The electronic structure of different clusters, containing up to 179 ions, has been computed for nine Cu:AX systems (A=Li,Na,K;X=F,Cl,Br). The calculations clearly show that the nearest-neighbor relaxations induced by impurity substitution are essentially determined by the substituted cation, the anion playing a rather minor role. In contrast with predictions deducible from empirical ionic radii, we find negligible or very small relaxations for Cu:LiX systems, and inward relaxations of about -0.1 Å for Cu:NaX systems [in very good agreement with recent extended x-ray absorption fine-structure (EXAFS) measurements on Cu:NaCl]. For the Cu:KX family we found inward relaxations as large as -0.3 Å. The stabilization energy associated to the substitution reaction turns out to range from -0.2 to -1.8 eV, with a remarkable dependence upon the substituted cation. The ${\mathit{t}}_{1\mathit{u}}$ frequencies, computed without including the intershell coupling, decrease with increasing cationic size, showing a trend that agrees with the experimental data reported by McClure for Cu:LiCl, Cu:NaF, and Cu:NaCl. Our methodology, in its present form, does not reproduce the off-center equilibrium position of the ${\mathrm{Cu}}^{+}$ ion observed in Cu:NaBr, Cu:KCl, and Cu:KBr.