This recently discovered superconductor is found to have a relatively low density of states with evidence for strong coupling. The critical field slope at ${\mathit{T}}_{\mathit{c}}$ is -0.5 T/K, consistent with the low specific heat γ of 11±2 mJ/mol ${\mathrm{K}}^2$.

We have experimentally studied the superconducting behavior of one-dimensional aluminum wires of various lengths. Each wire had much wider two-dimensional contact pads on both sides. At a temperature T below ${\mathit{T}}_{\mathit{c}}$, when the wide pads are driven normal by a perpendicular magnetic field, only samples longer than a critical length, ${\mathit{L}}_{\mathit{c}}$≃πξ(T), show evidence for superconductivity. This is a direct confirmation of the prediction by Liniger for a normal-metal–superconductor–normal-metal structure with clean interfaces.

An impurity in an unconventional superconductor can perturb the order parameter out to a distance of order the coherence length. This can lead to a large change in the density of states near an impurity. We compute the density of states as a function of position and frequency for a two-dimensional d-wave order parameter, while taking into account the effect of impurity scattering both in the Born and unitarity limits. We pay particular attention to the effect of anisotropy of the order parameter on the local density of states.

We contrast the effects of nonmagnetic impurities on the properties of superconductors having a ${\mathit{d}}_{{\mathit{x}}^2\mathrm{-}{\mathit{y}}^2}$ order parameter, and a highly anisotropic s-wave (ASW) gap with the same nodal structure. The nonvanishing, impurity-induced, off-diagonal self-energy in the ASW state is shown to inhibit the low-energy excitations present in the clean system, leading to a qualitatively different impurity response of the single-particle density of states compared to the ${\mathit{d}}_{{\mathit{x}}^2\mathrm{-}{\mathit{y}}^2}$ state. We discuss how this behavior can be employed to distinguish one state from the other by an analysis of high-resolution angle-resolved photoemission spectra.

The effects of structural disorder introduced by proton and heavy-ion irradiation on the mixed-state Hall resistivity (${\mathrm{\rho }}_{\mathit{xy}}$) of ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ films are reported. The ${\mathrm{\rho }}_{\mathit{xy}}$ attains a peak negative value at a temperature T* where the vortex mobility is a rapidly varying function of temperature. At T* it also shows a universal inverse scaling with the normal-state resistivity of the material, which increases on irradiation. Our data suggest that a stronger downstream contribution to vortex velocity from the drift of the normal carriers in the core, dictates the sign of the Hall voltage as the overall carrier concentration in the materials is reduced by irradiation.

Recently, a continuum theory of the mixed state in type-II superconductors was developed by two of us (Mathieu and Simon). An unorthodox model for the critical currents in soft materials proceeded from this theory. We show that this surface pinning model can be easily extended to soft high-${\mathit{T}}_{\mathit{c}}$ superconductors (HTSC’s). It successfully predicts the order of magnitude of critical currents such as observed in monocrystals or epitaxial films, and accounts for the existence and the position in the (H,T) plane of the irreversibility line. In the framework of our model, the vanishing of critical currents appears as a simple consequence of the strong anisotropy of HTSC’s; there is no need for any bulk phase transition of the vortex array.

The field (B) and temperature dependence of reversible magnetization M in Bi (2:2:1:2) single crystals is measured for the orientation of the field along the c axis. The slope of the curve M vs lnB decreases remarkably with field below 70 K. In the mean-field approach this slope should be almost B independent. We explain this change of slope by the quantum fluctuations of vortices. We show that for magnetization quantum fluctuations are important at all temperatures except in a narrow region near ${\mathit{T}}_{\mathit{c}}$.

We report on the temperature dependence of the far-infrared conductivity of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ single crystals for E∥c. With decreasing temperature, the conductivity shows a transition from a Drude-like behavior to a pseudogap at 180 ${\mathrm{cm}}^{\mathrm{-}1}$ which grows deeper below 180 K without any abrupt changes at the superconducting transition at ${\mathit{T}}_{\mathit{c}}$=80 K. In the superconducting state the formation of the superfluid condensate can be seen. We show that in a variety of high-${\mathit{T}}_{\mathit{c}}$ superconductors the value of the London penetration depth for E∥c correlates with the conductivity along the c direction. With respect to this correlation we discuss the possibility of Josephson coupling between the ${\mathrm{CuO}}_2$ layers.

The importance of the effects of mutual interactions between the interstitial solute atoms in the Cottrell atmosphere on the Snoek-Köster relaxation in cold-worked bcc metals is emphasized in a theoretical approach based on the coupling model. It is shown that the large activation enthalpy of the relaxation time and the breadth of the internal-friction peak associated with the Snoek-Köster relaxation can be explained quantitatively by this model for various foreign atoms in several bcc metals.

Face-centered-cubic iron (γ-Fe) coherently precipitated in a single crystal of Cu has been studied by neutron diffraction at high pressures up to 0.9 GPa and in the temperature range from about 5 to 110 K. It undergoes antiferromagnetic ordering at 67±2 K at ambient pressure. The ordering temperature ${\mathit{T}}_{\mathit{N}}$ monotonically decreases with increasing pressure following a relation ${\mathit{T}}_{\mathit{N}}$(K)=67-12.8p-11.1${\mathit{p}}^2$ -6.17${\mathit{p}}^3$, where p is in units of GPa. The change of ${\mathit{T}}_{\mathit{N}}$ in γ-Fe is discussed in terms of the volume change caused by pressurization or by alloying.

In ${\mathrm{CsCdBr}}_3$ the trivalent Pr ions substitute the divalent Cd ions. Charge compensation leads to Pr vacancy centers. By selective excitation and fluorescence spectroscopy and by annealing the crystals, three different Pr centers could be identified. The first one is the well-known symmetric pair center ${\mathrm{Pr}}^{3+}$–${\mathrm{Cd}}^{2+}$ vacancy–${\mathrm{Pr}}^{3+}$, the second one is the asymmetric pseudopair center ${\mathrm{Pr}}^{3+}$-${\mathrm{Pr}}^{3+}$-${\mathrm{Cd}}^{2+}$ vacancy, and the third one finally is a ${\mathrm{Pr}}^{3+}$ single ion with a ${\mathrm{Cs}}^{+}$ vacancy nearby. Energy-level schemes of all three centers were deduced from polarized site-selective spectra including the symmetries of the crystal-field states. Only the ${\mathrm{Pr}}^{3+}$-${\mathrm{Pr}}^{3+}$-${\mathrm{Cd}}^{2+}$ vacancy center showed upconversion emission from ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$ and ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ under pulsed ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ excitation.

A systematic high-resolution and high-statistics time-differential perturbed-angular-correlations study of the temperature dependence, from 77 to 1373 K, of the electric-field-gradient (EFG) tensor at ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ in ${\mathrm{HfO}}_2$ is presented. Three interactions were detected. One that was observed previously corresponds to the monoclinic structure, while the other two interactions have a reversible behavior with temperature and probably belong to equilibrium defect structures. The three components of the EFG tensor $V_{\mathrm{xx}}$, $V_{\mathrm{yy}}$, and $V_{\mathrm{zz}}$ corresponding to the monoclinic structure have different temperature behavior and are analyzed in terms of known models.

Spectral and polarization characteristics of luminescence of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers in KCl:Ge, KBr:Ge, and KI:Ge crystals have been studied in the temperature range 1.7–400 K. Several bands have been found in the emission spectrum of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers. Four emission bands originate from the Jahn-Teller tetragonal (T) minima of singlet and triplet relaxed excited states (RES), all split due to the existence of a cation vacancy (${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$) near the ${\mathrm{Ge}}^{2+}$ ion. Besides that, one or two red emission bands as well as a band situated between the singlet and triplet emission have also been observed in all the crystals investigated. Temperature dependences of intensities and polarization degrees of these emission bands have been studied, and the experimental manifestations of complicated relaxation and thermally stimulated processes in the excited states of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers as well as cation vacancy reorientations around the ${\mathrm{Ge}}^{2+}$ ion have been detected. Decay kinetics of the triplet emission of KCl:Ge and KCl${:}^{73}$Ge crystals have been studied at temperatures down to 0.35 K, and the parameters of the triplet RES have been determined. A considerable influence of the hyperfine, spin-orbit, and vibronic interactions and of the cation vacancy associated with the ${\mathrm{Ge}}^{2+}$ ion on the luminescence characteristics as well as on the parameters of the triplet RES of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers has been found. The possibility of an off-center displacement of an excited ${\mathrm{Ge}}^{2+}$ ion from the crystal-lattice site is discussed.

The nuclear-resonant-photon-scattering technique was utilized to monitor the iron binding properties in the intermetallic Zr(${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Fe}}_{1\mathrm{-}\mathit{x}}$${)}_2$ system. The ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ isotope scatters elastically 8.512-MeV γ rays emitted by a Cr(n,γ) source. An experimental comparison of the scattered intensity from the different compounds reflects the corresponding variation of the iron cohesion properties. The experimental results were quantified by evaluating the mean vibrational kinetic energies or effective temperatures, ${\mathit{T}}_{\mathit{e}}$, of the resonant iron nuclei in the specific compounds considered. The ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ effective temperature at room temperature was found to be 350(10), 337(16), 309(15), and 358(17) K for x=0, 0.083, 0.2, and 0.5, respectively. The results indicate clearly a minimum of the Fe bonding strength in the Zr(${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Fe}}_{1\mathrm{-}\mathit{x}}$${)}_2$ compounds at x=0.2. This minimum correlates nicely with the maximum hydrogen absorption in the above intermetallic system, which may be therefore considered to provide further support for the rule of reverse hydrogen absorption capacity. The conclusions of the present study are utilized to indicate ways for tailoring hydrogen absorption behavior in certain cases.

We analyze the structural, vibrational, and elastic properties of epitaxial novel FeSi films on Si(111) in the CsCl structure by Rutherford-backscattering spectrometry, x-ray-diffraction, infrared transmittance/ reflectance, and Brillouin-light-scattering measurements. By comparing our results for different film thicknesses and by interpreting them on the basis of semiempirical total-energy calculations, we are able to relate the changes in vibrational properties with the progressive strain relaxation as a function of sample thickness. For the thickest film (890 Å) we obtain indications that a structural transition to the (bulk) ε phase is about to take place.

Grain-boundary (GB) impurity diffusion of Au in Cu has been investigated by the radiotracer serial-sectioning technique using the ${}_{}{}^{195}{}_{}{}^{}\mathrm{Au}$ isotope with high specific activity. Measurements in the temperature ranges 618 to 1036 K and 450 to 526 K were carried out in Harrison’s type-B and type-C regimes, respectively. In the type-B regime, the product P=${\mathit{sD}}_{\mathrm{GB}}$δ was determined (s being the segregation factor, ${\mathit{D}}_{\mathrm{GB}}$ the GB-diffusion coefficient, δ the GB width), while in the type-C regime ${\mathit{D}}_{\mathrm{GB}}$ values were measured directly. Combining the obtained P and ${\mathit{D}}_{\mathrm{GB}}$ values and assuming δ=0.5 nm, the Au GB-segregation factor was evaluated. From the temperature dependence of s, the segregation enthalpy ${\mathit{H}}_{\mathit{s}}$=-9.7 kJ ${\mathrm{mol}}^{\mathrm{-}1}$ has been obtained. GB self-diffusion in Cu in the type-B regime has also been studied by the same experimental technique using the tracer ${}_{}{}^{64}{}_{}{}^{}\mathrm{Cu}$. The obtained ${\mathit{D}}_{\mathrm{GB}}$=P/δ values for self-diffusion are systematically larger than ${\mathit{D}}_{\mathrm{GB}}$ values for Au in Cu, whereas for lattice diffusion the opposite interrelation holds. This observation is discussed in terms of a trapping of Au atoms during impurity GB diffusion.

We present a thorough examination of the deterministic dynamics of finite, nonlinear, continuum systems which undergo elastic phase transitions. Particular attention is given to the correct implementation of open boundary conditions, which are nontrivial. As examples of the application of this formalism, in this paper we model two transformations: (i) The symmetry-preserving change of volume first-order transition undergone by some mixed-valence compounds, such as ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Th}}_{\mathit{x}}$. This example allows us to demonstrate how a bulk fluctuation that is subcritical (viz., does not nucleate product phase) can propagate to the surface and become supercritical (viz., does nucleate the transformed state) due to the greatly reduced nucleation barrier found at the system’s only heterogeneity, its surface. (ii) The late-stage dynamics of autocatalytic twinning undergone by shear martensites, such as discussed by Bales and one of us in Phys. Rev. Lett. 67, 3412 (1991). Such complete dynamical systems of equations involving a small number of continuum fields are a prerequisite for examining the rich sequences of patterns that form at these and other first-order transitions involving strains.

Internal friction due to diffusion of H and D atoms under stress was calculated for Ta(Nb)-H(D)-O(N) alloys. The long-range strain-induced (elastic) interaction was supplemented by a repulsive interaction in the nearest coordination shells due to a screened Coulomb interaction between charged interstitials. Short-range order in the interstitial solid solution was simulated by the Monte Carlo method. It was suggested that the interatomic interaction affects internal friction by changing the arrangement and the energy of H or D atoms in solid solution and therefore the activation energy of the relaxation process. Computer simulation was carried out with calculated values of energies of elastic interaction and with different radii of additional repulsive interaction. The calculated spectra are in good agreement with experimental data when the repulsive interaction extends out to the third coordination shell. The strain-induced interaction model, when supplemented by repulsion in the three nearest shells, is a useful description of these solid solutions.

The magnetic circular dichroism (MCD) of the absorption of ${\mathrm{Nb}}_{\mathrm{Li}}^{4+}$ and ${\mathrm{Ti}}_{\mathrm{Li}}^{3+}$ centers in ${\mathrm{LiNbO}}_3$ has been selectively measured by applying optically detected magnetic resonance. The attribution of a well-known broad and unstructured absorption band peaking at 1.6 eV to the ${\mathrm{Nb}}_{\mathrm{Li}}^{4+}$ bound small polaron is now unambiguously confirmed. In the MCD spectrum of the isoelectronic ${\mathrm{Ti}}_{\mathrm{Li}}^{3+}$ center, bands show up, which closely resemble the MCD bands at 1.6 eV of this bound small polaron. This striking similarity is explained by a cluster model, representing both defects. Either ${\mathrm{Ti}}_{\mathrm{Li}}$ or ${\mathrm{Nb}}_{\mathrm{Li}}$ is at the center of this cluster. In both cases, the small polaron is bound to the cluster, and its MCD bands correspond to intervalence transfer transitions within the constituents of the cluster. A study of the spin-orbit coupling of the molecular orbitals of the cluster allows one to analyze the structure of the MCD bands at 2.9 eV of ${\mathrm{Ti}}_{\mathrm{Li}}^{3+}$ have no counterpart in the ${\mathrm{Nb}}_{\mathrm{Li}}^{4+}$ spectrum. These bands are assigned to transitions to excited states, which are specific to the impurity and are related to the 10Dq transitions known for the crystal field states of a ${\mathit{d}}^1$ ion.