Condensed Matter
Formation of atomic pairs by the dissociation of a molecular condensate or by inelastic collisions in an atomic condensate due to a time-dependent curve crossing process is studied beyond the mean-field approximation. The number of atoms…
We have studied the magnetotransport properties in the normal state for a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y, between 0 and 0.12. A variable degree of compressive or tensile strain results from the lattice mismatch…
Spin-singlet and spin-triplet internal transitions of quasi-two-dimensional, negatively charged magneto-excitons (X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum-wells by optically detected…
The first global quantum simulation of semiconductor-based quantum-cascade lasers is presented. Our three-dimensional approach allows to study in a purely microscopic way the current-voltage characteristics of state-of-the-art unipolar…
A detailed analysis of the electro-optical response of single as well as coupled semiconductor quantum dots is presented. This is based on a realistic ---i.e., fully tridimensional--- description of Coulomb-correlated few-electron states,…
When a thin elastic sheet crumples, the elastic energy condenses into a network of folding lines and point vertices. These folds and vertices have elastic energy densities much greater than the surrounding areas, and most of the work…
Epitaxial ferromagnetic metal - semiconductor heterostructures are investigated using polarization-dependent electroabsorption measurements on GaAs p-type and n-type Schottky diodes with embedded In1-xGaxAs quantum wells. We have conducted…
We propose a double exchange model to describe the RuO_2 planes of RuSr_2(Eu,Gd)Cu_2O_8. The Ru^+5 ions are described by localized spins, and additional electrons provided by the superconducting CuO_2 planes are coupled ferromagnetically to…
Experimental evidence show that in the magnetoresistive manganite Ca_(1-x) Y_xMnO_3, ferromagnetic (FM) polarons arises in an antiferromagnetic (AF) background, as a result of the doping with Yttrium. This hypothesis is supported in this…
We review recent theoretical progress on the dynamics of brittle crack fronts and its relationship to the roughness of fracture surfaces. We discuss the possibility that the intermediate scale roughness of cracks, which is characterized by…
We present a scheme to identify quasicrystals based on powder diffraction data and to provide a standardized indexing. We apply our scheme to a large catalog of powder diffraction patterns, including natural minerals, to look for new…
First principles density functional calculations within the local spin density approximation (LSDA) and the generalized gradient approximation (GGA) are reported for pyrochlore Cd$_2$Os$_2$O$_7$ and Cd$_{2}$Re$_{2}$O$_7$. The transition…
We report Hall sensor measurements of the magnetic relaxation of Mn$_{12}$-acetate as a function of magnetic field applied along the easy axis of magnetization for a series of closely-spaced temperatures between 0.24 K and 1.9 K. We map out…
Two methods are compared that are used in path integral simulations. Both methods aim to achieve faster convergence to the quantum limit than the so-called primitive algorithm (PA). One method, originally proposed by Takahashi and Imada, is…
A two dimensional magnetic particle in the presence of an external magnetic field is studied. Equilibrium thermodynamical properties are derived by evaluating analytically the partition function. When the external field is applied…
Density functional calculations are used to study magnetic and electronic properties of the spinel ferrites, ZnFe$_2$O$_4$ and MnFe$_2$O$_4$. Correct magnetic orderings are obtained. ZnFe$_2$O$_4$ is predicted to be a small gap insulator in…
Well known Bethe strings in spin chains, delta-electron gas, Hubbard and t-J models are shown to be imprecise, while their consisten refinement along with a new non-Bethe r-string are discovered. Connection with the earlier results is…
Using an exact mapping to disordered Coulomb gases, we introduce a novel method to study two dimensional Dirac fermions with quenched disorder in two dimensions which allows to treat non perturbative freezing phenomena. For purely random…
The static polarizability of cylindrical systems is shown to have a strong dependence on a uniform magnetic field applied parallel to the tube axis. This dependence is demonstrated by performing exact numerical diagonalizations of simple…
One of the major differences between fermions and bosons is that fermionic states have a maximum occupation number of one, whereas the occupation number for bosonic states is in principle unlimited. For bosons that are made up of fermions,…