First Results from the HDMS experiment in the Final Setup

The Heidelberg Dark Matter Search (HDMS) is an experiment designed for the search for WIMP dark matter. It is using a special configuration of Ge detectors, to efficiently reduce the background in the low-energy region below 100 keV. After one year of running the HDMS detector prototype in the Gran Sasso Underground Laboratory, the inner crystal of the detector has been replaced with a HPGe crystal of enriched $^{73}$Ge. The final setup started data taking in Gran Sasso in August 2000. The performance and the first results of the measurement with the final setup are discussed.Comment: 8 pages, revtex, 7 figures, Home Page of Heidelberg Non-Accelerator Particle Physics Group: http://www.mpi-hd.mpg.de/non_acc

Observation of a temperature dependent electrical resistance minimum above the magnetic ordering temperature in Gd2_2PdSi3_3

Results on electrical resistivity, magnetoresistance, magnetic Results on electrical resistivity, magnetoresistance, magnetic susceptibility, heat capacity and Gd Mossbauer measurements on a Gd-based intermetallic compound, Gd$_{2}$PdSi$_{3}$ are reported. A finding of interest is that the resistivity unexpectedly shows a well-defined minimum at about 45 K, well above the long range magnetic ordering temperature (21 K), a feature which gets suppressed by the application of a magnetic field. This observation in a Gd alloy presents an interesting scenario. On the basis of our results, we propose electron localization induced by s-f (or d-f) exchange interaction prior to long range magnetic order as a mechanism for the electrical resistance minimum.Comment: 4 pages, 4 figure

Suppression of the ferromagnetic state in LaCoO3 films by rhombohedral distortion

Epitaxially strained LaCoO3 (LCO) thin films were grown with different film thickness, t, on (001) oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates. After initial pseudomorphic growth the films start to relieve their strain partly by the formation of periodic nano-twins with twin planes predominantly along the direction. Nano-twinning occurs already at the initial stage of growth, albeit in a more moderate way. Pseudomorphic grains, on the other hand, still grow up to a thickness of at least several tenths of nanometers. The twinning is attributed to the symmetry lowering of the epitaxially strained pseudo-tetragonal structure towards the relaxed rhombohedral structure of bulk LCO. However, the unit-cell volume of the pseudo-tetragonal structure is found to be nearly constant over a very large range of t. Only films with t > 130 nm show a significant relaxation of the lattice parameters towards values comparable to those of bulk LCO.Comment: 31 pages, 10 figure

Conversion of an Atomic Fermi Gas to a Long-Lived Molecular Bose Gas

We have converted an ultracold Fermi gas of $^6$Li atoms into an ultracold gas of $^6$Li$_2$ molecules by adiabatic passage through a Feshbach resonance. Approximately $1.5 \times 10^5$ molecules in the least-bound, $v = 38$, vibrational level of the X$^1 \Sigma ^+_g$ singlet state are produced with an efficiency of 50%. The molecules remain confined in an optical trap for times of up to 1 s before we dissociate them by a reverse adiabatic sweep.Comment: Accepted for publication in Phys. Rev. Letter

Transmission electron microscopy investigation of segregation and critical floating-layer content of indium for island formation in InGaAs

We have investigated InGaAs layers grown by molecular-beam epitaxy on GaAs(001) by transmission electron microscopy (TEM) and photoluminescence spectroscopy. InGaAs layers with In-concentrations of 16, 25 and 28 % and respective thicknesses of 20, 22 and 23 monolayers were deposited at 535 C. The parameters were chosen to grow layers slightly above and below the transition between the two- and three-dimensional growth mode. In-concentration profiles were obtained from high-resolution TEM images by composition evaluation by lattice fringe analysis. The measured profiles can be well described applying the segregation model of Muraki et al. [Appl. Phys. Lett. 61 (1992) 557]. Calculated photoluminescence peak positions on the basis of the measured concentration profiles are in good agreement with the experimental ones. Evaluating experimental In-concentration profiles it is found that the transition from the two-dimensional to the three-dimensional growth mode occurs if the indium content in the In-floating layer exceeds 1.1+/-0.2 monolayers. The measured exponential decrease of the In-concentration within the cap layer on top of the islands reveals that the In-floating layer is not consumed during island formation. The segregation efficiency above the islands is increased compared to the quantum wells which is explained tentatively by strain-dependent lattice-site selection of In. In addition, In0.25Ga0.75As quantum wells were grown at different temperatures between 500 oC and 550 oC. The evaluation of concentration profiles shows that the segregation efficiency increases from R=0.65 to R=0.83.Comment: 16 pages, 6 figures, 1 table, sbmitted in Phys. Rev.

A model for conservative chaos constructed from multi-component Bose-Einstein condensates with a trap in 2 dimensions

To show a mechanism leading to the breakdown of a particle picture for the multi-component Bose-Einstein condensates(BECs) with a harmonic trap in high dimensions, we investigate the corresponding 2-$d$ nonlinear Schr{\"o}dinger equation (Gross-Pitaevskii equation) with use of a modified variational principle. A molecule of two identical Gaussian wavepackets has two degrees of freedom(DFs), the separation of center-of-masses and the wavepacket width. Without the inter-component interaction(ICI) these DFs show independent regular oscillations with the degenerate eigen-frequencies. The inclusion of ICI strongly mixes these DFs, generating a fat mode that breaks a particle picture, which however can be recovered by introducing a time-periodic ICI with zero average. In case of the molecule of three wavepackets for a three-component BEC, the increase of amplitude of ICI yields a transition from regular to chaotic oscillations in the wavepacket breathing.Comment: 5 pages, 4 figure

Matter-wave soliton control in optical lattices with topological dislocations

We address the concept of guiding and transporting matter-wave solitons along the channels of optical lattices made by interference patterns of beams containing topological wavefront dislocations. The local lattice distortions that occur around the dislocations cause solitons to move along reconfigurable paths, a phenomenon that may be used for controlled all-optical manipulation of Bose-Einstein condensates. Multiple dislocations form traps that can capture and hold moving solitons.Comment: 15 pages, 4 figures, to appear in Physical Review