Nodal quasiparticle lifetime in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8+delta)

We have measured the complex conductivity sigma of a Bi(2)Sr(2)CaCu(2)O(8+delta) thin film between 0.2 and 0.8 THz. We find sigma in the superconducting state to be well described as the sum of contributions from quasiparticles, condensate, and order parameter fluctuations which draw 30% of the spectral weight from the condensate. An analysis based on this decomposition yields a quasiparticle scattering rate on the order of k(B)T/Planck's over 2pi for temperatures below T(c).     

Viscous spin exchange torque on precessional magnetization in (LaMnO3)2n/(SrMnO3)n superlattices

Photoinduced magnetization dynamics is investigated in chemically ordered (LaMnO3)2n/(SrMnO3)n superlattices using the time-resolved magneto-optic Kerr effect. A monotonic frequency-field dependence is observed for the n=1 superlattice, indicating a single spin population consistent with a homogeneous hole distribution. In contrast, for n> or =2 superlattices, a large precession frequency is observed at low fields indicating the presence of an exchange torque in the dynamic regime. We attribute the emergence of exchange torque to the coupling between two spin populations-viscous and fast spins.     

Mesoscopic thermodynamics of an inhomogeneous colossal-magnetoresistive phase

Equilibrium conductivity fluctuations of mesoscopic domains are found in film and bulk single-crystal manganite colossal magnetoresistive material. Temperature and field dependences of the Boltzmann factors for a collection of two-state fluctuators give measures of the magnetic moment and entropy differences between the states, and of the fluctuator volumes. The large resistance step size implies dramatic current inhomogeneities. Occasional anomalous temperature dependences indicate that the film inhomogeneous phase is stabilized by a repulsive interaction between conducting regions.     

Permittivity,dielectric loss and dc conductivity of NaNO3 crystals grown by epitaxy

The temperature dependence of the d.c. conductivity, the dielectric loss and the permittivity of NaNO₃ single crystals prepared by epitaxial accretion of the (111) plane of NaNO₃ on the (001) plane of mica were investigated. The measurements were performed in a temperature range from 20–300C. Below the melting point a region of intrinsic conductivity (U _I=3·08 eV), caused by Na⁺ ions which are in interstitial sites, was observed. At lower temperature a region II (U _II= 0·87 eV), where the conductivity is due to the presence of divalent impurities, probably Ca^{+ +} followed (structurally sensitive region). Up to 250C polarization is observed, most probably due to ion and electron shifting only. Above that temperature the influence of the relaxed orientation of the NO ₃ ^– groups becomes evident. At 275C the NO ₃ ^s- groups behave in a completely disordered way as indicated by a sudden increase of the permittivity plotted against temperature.We should like to express our gratitude to RNDr. A. Kessler, DrSc, for his very valuable advice.     

Einige Physikalische Eigenschaften Grosser CdS-Einkristalle

The author grew CdS single crystals by his own method which is described here in addition to other methods. The material was either prepared by the author or commercial luminescence-pure material was used. The amount of impurities in the commercial material was an order higher than in the author's own material. It was found that the physical properties (e.g. hole density) are worse in large single crystals than in crystals with a mosaic structure. For this reason it is thought that some of the properties are caused by stoichiometric deviations and other by defects in the crystal lattice. In this case impurification plays only a secondary role.     

Sputtering studies with the Monte Carlo Program TRIM.SP

The Monte Carlo Program TRIM.SP (sputtering version of TRIM) was used to determine sputtering yields and energy and angular distributions of sputtered particles in physical (collisional) sputtering processes. The output is set up to distinguish between the contributions of primary and secondary knock-on atoms as caused by in- and outgoing incident ions, in order to get a better understanding of the sputtering mechanisms and to check on previous theoretical models. The influence of the interatomic potential and the inelastic energy loss model as well as the surface binding energy on the sputtering yield is investigated. Further results are sputtering yields versus incident energy and angle as well as total angular distributions of sputtered particles and energy distributions in specific solid angles for non-normal incidence. The calculated data are compared with experimental results as far as possible. From this comparison it turns out that the TRIM.SP is able to reproduce experimental results even in very special details of angular and energy distributions.     

Metal-insulator transition and its relation to magnetic structure in (LaMnO3)2n/(SrMnO3)n superlattices

Superlattices of (LaMnO3){2n}/(SrMnO3){n} (1or=3. Measurements of transport, magnetization, and polarized neutron reflectivity reveal that the ferromagnetism is relatively uniform in the metallic state, and is strongly modulated in the insulating state, being high in LaMnO3 and suppressed in SrMnO3. The modulation is consistent with a Mott transition driven by the proximity between the (LaMnO3)/(SrMnO3) interfaces. The insulating state for n>or=3 obeys variable range hopping at low temperatures. We suggest that this is due to states at the Fermi level that emerge at the (LaMnO3)/(SrMnO3) interfaces and are localized by disorder.