First-principles calculations have been performed for the clean K(110) surface. The results provide no evidence for the existence of a 0.23 Å shear displacement of the surface layer along the [1¯10] direction as was inferred from an analysis of low-energy electron diffraction I-V profiles [Itchkawitz et al., Phys. Rev. Lett. 68, 2488 (1992)]. They do indicate, however, that the surface layer undergoes large-amplitude vibrations (∼0.45 Å root mean squared) along the [1¯10] direction and it is argued that this feature accounts for the experimental observations.

Measurements between 0.05 and 1 K in magnetic fields small enough to ensure linear response (B<1 T) indicate that the Hall coefficient of Si:B diverges at the metal-insulator transition. This is similar to Ge:Sb and differs from the finite behavior claimed for Si:As and Si:F. Our result may be due to strong spin-orbit effects; it is inconsistent with a recent suggestion that the Hall coefficient is finite in systems with critical conductivity exponent μ≊1/2.

An analytic expression for the dynamic structure factor S(k,ω) of a 3D electron gas is obtained by the recurrence relation method. It is valid for one metallic density ${\mathit{r}}_{\mathit{s}}$≊3.5 and is exact asymptotically, i.e., k≫${\mathit{k}}_{\mathit{F}}$ (${\mathit{k}}_{\mathit{F}}$ the Fermi wave vector). The result is based on an assumption, justified by the kinetic-energy and static-structure-factor sum rules and also numerically approximately corroborated. The expression is compared with an experimental measurement of Li at k=2.08${\mathit{k}}_{\mathit{F}}$.

We extend and generalize the notion of ensemble averaging in the context of the thermodynamics of mesoscopic systems. Two important factors determine the statistical ensemble: (i) Constraints imposed on the system as external fields are varied adiabatically; (ii) the initial preparation of the ensemble. Different procedures correspond to different experimental setups, and may result in different magnitude, sign, and Aharonov-Bohm periodicity of the quantity at hand. Adiabatic dynamical response is related to one of these static averaging procedures.

The localization of the wave functions in a random magnetic field in 2D is investigated numerically in terms of MacKinnon’s finite size scaling method. The single-parameter scaling relation is confirmed, and the scaling function β(g) (g is the dimensionless conductance) obtained for this unitary model is consistent with the recent analytical result up to ${\mathit{g}}^{\mathrm{-}4}$, indicating that all the wave functions are localized.

We consider transport in a quantum-coherent system containing a ballistic region and disordered reservoirs connected to it. The ballistic region works as a filter: It suppresses conductance fluctuations that are due to disorder and recovers conductance quantization. However, the suppression is much weaker than that predicted by Ohm’s law for classical resistors in series.

Random matrix theory of the transition strengths is applied to transport in the strongly localized regime. The crossover distribution function between the different ensembles is derived and used to predict quantitatively the universal magnetoconductance curves in the absence and in the presence of spin-orbit scattering. These predictions are confirmed numerically.

The valence and core level spectra of chemically prepared, ideally H-terminated Si(111) surfaces are characterized by remarkably sharp features. The valence band levels and their dispersion are well described by first-principles calculations using a quasiparticle self-energy approach within the GW approximation. From the ${\mathrm{Si}}_{2\mathit{p}}$ spectra, an upper limit of 35±10 meV is derived from the core hole lifetime broadening, a value substantially lower than previously measured.

We report on a theoretical treatment of the Esaki-Tsu superlattice oscillator emphasizing a profound link between the dynamics of charge carriers in a superlattice and the dynamics of Josephson junctions. Using a balance-equation aproach we calculate the oscillator efficiency taking account fo the negative effective mass that carriers can have in a miniband and of dissipation. We show that emission of electromagnetic radiation from currently available superlattices can occur due to multiphoton transitions from almost zero up to terahertz frequencies.

A new and general method to separate x-ray absorption (XA) features is presented. The XA spectrum is monitored by detailed recordings of autoionization data. The technique is applied to the ${\mathrm{N}}_2$/Ni(100)c(2×2) system, for which the N 1s 2π resonance is separated into the two components originating from the inequivalent nitrogen atoms. The XA peaks exhibit large differences in line shape, which is successfully explained in terms of the hybridization strengths of the XA final states. The total intensities of the XA peaks provide important information regarding the ground state of the adsorbed molecule.

We observe that the semiclassical Hall constant for a strongly correlated Fermi system is most directly related to the high frequency Hall conductivity. For the square lattice, the sign of the latter is found to be holelike (while the Fermi surface is electronlike) for fillings close to half, and electronlike for almost empty bands. For the t-J model on the square lattice in two dimensions the change of sign occurs at roughly 1/3 hole filling in good agreement with measurements on ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$ compounds, and is weakly temperature dependent. We suggest that the high frequency Hall constant can be directly measured in a Faraday rotation experiment.

the heavy-fermion superconductor ${\mathrm{UPt}}_3$ has been studied in the superconducting state down to 36 mK by point-contact spectroscopy. Distinct minima in the differential resistance dV/dI versus voltage V related to the energy gap are observed for current flow parallel to the crystallographic c axis, while for current flow within the basal plane such features were almost always absent. This difference, together with a comparison of the Blonder-Tinkham-Klapwijk theory, gives clear evidence for a strong gap anisotropy. This is further supported by the unusual temperature and magnetic-field dependence of the spectra.

The anisotropic resistivity components of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ have been measured from 0 to 900 K. ${\mathrm{YBa}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ is an underdoped, genuinely untwinned, and stoichiometric high temperature superconductor. The ${\mathrm{CuO}}_2$ plane resistivity ${\mathrm{\rho }}_{\mathit{a}}$ exhibits a strong correlation with the spin dynamics, i.e., with Knight shift and spin-lattice relaxation time ${\mathit{T}}_1$. The resistivity along the b axis (plane plus chain) is consistent with Bloch-Grüneisen theory. The cotangent of the Hall angle is quadratic in temperature above the spin gap, and linear below.

We study the continuum limit of the spin-1 chain in the non-Abelian bosonization approach of Affleck and show that the Hamiltonian of the integrable spin-1 chain yields the Lagrangian of the supersymmetric sine-Gordon model in the zero lattice spacing limit. We also show that the quantum group generators of the spin-1 chain give nonlocal charges of the supersymmetric sine-Gordon theory.

We report measurements of the magnetic response of a GaAlAs/GaAs mesoscopic ring. We have developed a dedicated SQUID technique where sample and SQUID are on the same chip. We have detected a periodic signal, with a period h/e, which is the signature of a persistent current with an amplitude 4±2 nA, in good agreement with current theories.

We show exactly that the ground state of the Anderson lattice with U=∞ is ferromagnetic at quarter filling if the level of localized electrons ${\mathit{s}}_{\mathit{f}}$ is deep enough: ${\mathrm{\varepsilon }}_{\mathit{f}}$<${\mathrm{\varepsilon }}_{\mathit{f}\mathit{c}}$, where ${\mathrm{\varepsilon }}_{\mathit{f}\mathit{c}}$ is of the order of the bandwidth. Rigorous arguments show that if ${\mathrm{\varepsilon }}_{\mathit{f}}$<${\mathrm{\varepsilon }}_{\mathit{f}\mathit{c}}$, the ground state has the total spin S=(N-1)/2 for ${\mathit{N}}_{\mathit{e}}$=N+1 and S=${\mathit{N}}_{\mathit{e}}$/2 for ${\mathit{N}}_{\mathit{e}}$≤N, where N is the number of lattice sites and ${\mathit{N}}_{\mathit{e}}$ is that of electrons. At quarter filling, this indicates that a transition to an insulating magnetically ordered ground state will occur for a value of ${\mathrm{\varepsilon }}_{\mathit{f}}$ less than ${\mathrm{\varepsilon }}_{\mathit{f}\mathit{c}}$. We observe this transition for finite U if -${\mathrm{\varepsilon }}_{\mathit{f}}$ is sufficiently large.

We study dissipative patterns caused by spin-wave instabilities in insulating ferromagnetic films which are driven by out-of-plane parallel pumping. Using a multiple-scale perturbation method, we derive amplitude equations for magnetostatic modes with wavelengths much larger than the film thickness, and study the stability of solutions with constant amplitudes. The main result is that the only stable patterns are squares, hexagons, and quasiperiodic patterns based on three standing waves. Quantitative results strongly support the suggestion that these patterns should be experimentally observable by means of Faraday rotation.

${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ Mössbauer studies under hydrostatic pressures up to 41 GPa coupled to x-ray diffraction measurements show that—contrary to expectations—the 4f electrons in ${\mathrm{EuAl}}_2$ remain fully localized even under a reduction of unit cell volume of ∼30%. However, strongly nonlinear effects are observed for the conduction electron polarization, for the s-electron density ρ(0) at the ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$ nucleus, the Néel temperature ${\mathit{T}}_{\mathit{N}}$, and the transferred hyperfine field hyperbolically; ${\mathit{T}}_{\mathit{N}}$ and ${\mathit{B}}_{\mathrm{thf}}$ connected to ρ(0). The latter results can be described quantitatively within the RKKY formalism.

Multistep photon absorption has been used to measure the collective excitation of free lithium clusters having up to 1500 atoms. The blueshift of the Mie resonance energy, as cluster size increases, probes the surface effects. Its absolute vlaue is consistent with the dielectric constants of the bulk down to a 100 atom cluster. The comparison with calculations in random-phase approximation in the local approximation demonstrates that the jellium model is no longer valid for lithium clusters.

Using a scanning tunneling microscope, single adatoms can be extracted from a Si(111)7×7 surface by field evaporation, when the sample voltage is pulsed at 4 V or more in either polarity. Statistically, adatoms at the center of the 7×7 unit cell are more frequently removed than those near the corner holes, by a ratio of 1.6:1. This difference can be explained by assuming that the binding energy of center adatoms is approximately 0.01 eV less than for corner adatoms. The relationship of this result to previous observations of greater chemical reactivity at center adatom sites is discussed.