Table of contents

The conductance of a ballistic quantum dot (having chaotic classical dynamics and being coupled by ballistic point contacts to two electron reservoirs) is computed on the single assumption that its scattering matrix is a member of Dyson's circular ensemble. General formulae are obtained for the mean and variance of transport properties in the orthogonal (β = 1), unitary (β = 2), and symplectic (β = 4) symmetry class. Applications include universal conductance fluctuations, weak localization, sub-Poissonian shot noise, and normal-metal-superconductor junctions. The complete distribution P(g) of the conductance g is computed for the case that the coupling to the reservoirs occurs via two quantum point contacts with a single transmitted channel. The result P(g) ∝ g^{−1 + β/2} is qualitatively different in the three symmetry classes.

We present results of numerical simulations of kinetic roughening for a growth model with surface diffusion (the Wolf-Villain model) in 3 + 1 and 4 + 1 dimensions using lattices of a linear size up to L = 64 in 3 + 1 D and L = 32 in 4 + 1 D. The effective exponents calculated both from the surface width and from the height-height correlation function are much larger than those expected based on results in lower dimensions, due to a growth instability which leades to the evolution of large mounded structures on the surface. An increase of the range for incorporation of a freshly deposited particle leads to a decrease of the roughness but does not suppress the instability.

We present high-resolution photoelectron spectra and angular distributions produced by multiphoton ionization of Ar and Xe atoms by intense ultrashort laser pulses. The measurements have been performed in order to investigate the connection between two recently discovered effects in above-threshold ionization, namely a plateau in the photoelectron spectra and side lobes in the corresponding angular distributions. The side lobes are found to be restricted to the region where the plateau begins. This affords a new explanation of the origin of the side lobes.

We present measurements of the intensity dependence of excited-state collisions of laser-cooled ⁸⁵Rb atoms involving repulsive excited-state potentials. For high intensities, the collision rate decreases with increasing intensity, in accordance with a simple Landau-Zener treatment of the collision dynamics.

Owing to the rotation of the two-centre Coulomb potential during ion-atom collisions, electrons can be stabilized on the saddle of the potential and promoted to excited levels. The results of recent experiments on ion impact excitation of He atoms at intermediate energies are explained by this Paul-trap mechanism.

The static structure factor of the dilute sterically stabilised lamellar phase is calculated and found to have an Ornstein-Zernike form with a correlation length that diverges at infinite dilution. The relaxation time for concentration fluctuations at large wave number q is shown to go as q^-3 with a coefficient independent of the membrane bending rigidity. The membrane fluctuations also give rise to strongly frequency-dependent viscosities at high frequencies.

Phase separation dynamics with an initially nonuniform concentration are studied. Critical and off-critical behavior is observed simultaneously. A mechanism for an expanding phase-separated region is demonstrated and the time dependence of the concentration is determined. The final equilibrium state consists of a planar interface separating one phase from the other. The evolution to this state is characterized by an experimentally observable flux, j, crossing this interface. We find that j ∼ t^−2/3 if patterns are formed in the bulk and j ∼ t^−1/2 if the bulk remains homogeneous. The results are explained in terms of scaling arguments which are confirmed numerically.

In view of a recent controversy we investigated the Mott-Hubbard transition in D = ∞ with a novel cluster approach. i) We show that any truncated Bethe lattice of order n can be mapped exactly to a finite, Hubbard-like cluster. ii) We evaluate the self-energy numerically for n = 0, 1, 2 and compare with a series of self-consistent equation-of-motion solutions. iii) We find the gap to open continuously at the critical U_c ∼ 2.5t* (t ≡ t* /√(4d)). iv) A low-energy theory for the Mott-Hubbard transition is developed and relations between critical exponents are presented.

In this letter we use the replica trick together with a variational method in order to compute the effective conductivity tensor of a disordered binary composite in a static magnetic field. When only of the two components percolates, the effective magnetoresistivity ρ_xx^(e) saturates for strong magnetic fields h as in a homogeneous material. When both components percolate, the effective magnetoresistivity displays an anomalous behaviour and scales like the magnetic field h. At the percolation threshold of one component (denoted by p_c), the scaling exponent ν (ρ_xx^(e) ∼ h^ν) is equal to 2/3 and there is a scaling behaviour with both h and p − p_c (where p denotes the volume fraction). This indicates that there is a field-dependent correlation length at strong fields that is distinct from the percolation correlation length. In all cases the effective Hall constant R_H saturates at strong fields.

The transport of an N-channel spinless interacting electron gas through an ultrasmall normal tunnel junction coupled to a circuit with Ohmic impedance is studied and the current-voltage characteristics are calculated. We give a simple description in terms of an effective density of states of quasi-particles involved in the tunnelling process. This picture also proves useful for cotunnelling of interacting electrons in multijunction systems.

We propose a variational approach to the problem of roughening of interfaces in random media. This method does not introduce replicas, and reproduces the Imry-Ma-Villain roughening exponent ζ for the width of the interface, in random field problems. The method can also be applied to random bond problems, and it provides a microscopic basis for these types of scaling arguments. In addition, it allows to calculate the probability distribution for the width of the interface, as well as the fluctuations of the free energy.

The ejection process in solid krypton following electronic de-excitation has been studied with molecular-dynamics simulations. We have introduced a new model for the excimer formation that includes the interaction between the excimer and the lattice. The excimer migrates up to 5 Å before it decays radiatively to the repulsive part of the ground state. Long-range collision sequences along lattice rows contribute significantly to the sputtering yield. The kinetic-energy distribution of sputtered particles based on this model agrees well with the experimental spectrum.

The question of boson realization of fermions is considered in the general context of q-deformation.

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