Photochromie von Dimethylthiathiophthen und N-Analoǵa von Thiathiophthenen

Irradiation of N-analogs of thiathiophthenes and dimethylthiathiophthene yield a transient which reverts thermally to the starting product. Kinetic measurements for this thermal reaction yield E_a values in the range of 9–14 kcal/mol and ΔS^≠ values between – 10 and – 30 e.u. The structure of the transient is discussed based on these data, its electronic and infrared spectrum.     

Longitudinal field relaxation measurements in monocrystalline DyAl2

Longitudinal μSR measurements were performed on a single crystal sphere of DyAl₂ in the range 4K≤T≤300 K (i.e. both in the ferromagnetic and paramagnetic phases). Contrary to previous reports the dynamic depolarization rate does not diverge near T_C≌65 K. Rather a well defined peak in the depolariation rate is observed around 95 K with 1/T₁ (95 K)∼4 μsec⁻¹. The depolariztion rate above T_C is field independent in the range 0≤B_ext≤2.5 kG. The observed behavior may be accounted for by assuming that the effective correlation time τ is given by τ⁻=τ _4f ⁻¹ +τ _diffusion ⁻¹ . The field independence requires that τ_eff<2·10⁻¹¹. The peak in 1/T₁ could then reflect a slowing down in μ⁺.     

Stability properties of nonhyperbolic chaotic attractors with respect to noise

We study local and global stability of nonhyperbolic chaotic attractors contaminated by noise. The former is given by the maximum distance of a noisy trajectory from the noisefree attractor, while the latter is provided by the minimal escape energy necessary to leave the basin of attraction, calculated with the Hamiltonian theory of large fluctuations. We establish the important and counterintuitive result that both concepts may be opposed to each other. Even when one attractor is globally more stable than another one, it can be locally less stable. Our results are exemplified with the Holmes map, for two different sets of parameter, and with a juxtaposition of the Holmes and the Ikeda maps. Finally, the experimental relevance of these findings is pointed out.     

Muon Spin Dynamics and Sites in GdNi5

In GdNi₅, the muon localizes at the 3f interstitial site and below 80K a second muon site becomes populated, the so-called 6_ring site. This ring site is metastable and the muon hops to the 3f site. We determine the mean time of stay of the muon in the ring site and show that it is governed by a multi-phonon quantum diffusion process. The coincidence energy is measured to be E _a =272(10)K and the tunneling matrix element J=0.11(2)meV.     

Magnetic penetration depth in the Chevrel phase superconductors SnMo6SySe8−y and PbMo6SzSe8−z

We report on transverse field (300 mT)μ ⁺ SR measurements in the Chevrel phase superconductors SnMo₆S_ySe_8−y (y=1, 4, 7, 8) and PbMo₆S_zSe_8−z (z=4.8) using the field cooling procedure (from room temperature down to 2.2 K). The London penetration depth λ_L was determined by the analysis of the fits with a single Gaussian relaxation function and by comparing the measured field distributions with calculated ones, where a broadening due to small random displacements of the vortices was taken into account.     

A μSR study of the 1 K phase transition in the heavy electron compound UCu5

The 1 K phase transition in UCu₅, which shows up in specific heat data within the antiferromagnetic state belowT _N =16 K, was investigated by zero field μSR. The data reveal a pronounced increase in the internal field spread at theμ ⁺ sites below 1.2 K while the average fields seem to be unaffected. These results are compatible with the onset of a charge density wave state below 1.2 K.