Stable vortex-antivortex molecules in mesoscopic superconducting triangles

A thermodynamically stable vortex-antivortex pattern has been revealed in equilateral mesoscopic type I superconducting triangles, contrary to type II superconductors where similar patterns are unstable. The stable vortex-antivortex "molecule" appears due to the interplay between two factors: a repulsive vortex-antivortex interaction in type I superconductors and the vortex confinement in the mesoscopic triangle.     

Anomalous magnetic properties of the complex (ET)2C60

Investigations of the temperature dependences of the magnetic permeability and dielectric permittivity in the temperature range 4.2 K⩽T ⩽300 K and the field dependence of the magnetization M(B) in fields B⩽50 T show that the magnetic properties of the complex (ET)₂C₆₀ cannot be described on the basis of the standard model, which assumes that the paramagnetic oxygen impurity makes the dominant contribution. It is found that the magnetism in (ET)₂C₆₀ is due to the diamagnetic properties of the C₆₀ and ET molecules and to specific paramagnetic centers of the type C ₆₀ ⁻ , which possess an anomalously low g factor |g|≈0.14. An experimentum crucis is proposed for checking the oxygen paramagnetic center model for pure C₆₀ films. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 10, 733–738 (25 May 1999)     

Sol–gel preparation and white up-conversion luminescence in rare-earth doped PbF<Subscript>2</Subscript> nanocrystals dissolved in silica glass

89.5(SiO₂)10(PbF₂)0.5(REF₃) silicate glasses have been prepared using room temperature sol–gel processing of Si(OCH₂CH₃)₄, Pb(CH₃COO)₂·3H₂O, RE(CH₃COO)₃·nH₂O and trifluoroacetic acid as a fluorinating agent, where RE stands for rare-earth ions, such as Yb³⁺, Er³⁺, Ho³⁺, Tm³⁺, or combinations of those ions. On heat treatment of these glasses at about 300–400 °C, the rare-earth doped spherical PbF₂ nanocrystals precipitate within SiO₂ glass matrix providing transparent nano-structured glass–ceramics, while the diameter of the nanocrystals can be set in the range from 5 to 25 nm by varying time and temperature of the heat treatment. The structural and photoluminescence studies confirm the incorporation of rare-earth ions into the PbF₂ nanocrystals and white and tuneable colour up-conversion luminescence has been detected in case of Yb³⁺-Er³⁺-Tm³⁺ and Yb³⁺-Ho³⁺-Tm³⁺ co-doped nanocrystals by varying dopant ratio and pump power.     

Vortex core deformation and stepper-motor ratchet behavior in a superconducting aluminum film containing an array of holes

We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time-dependent Ginzburg-Landau formalism. We demonstrate that the high frequency vortex behavior can be described as a discrete motion of a particle in a periodic potential, i.e., the so-called stepper-motor behavior. Strikingly, in the more conventional low frequency response a transition takes place from an Abrikosov vortex rectifier to a phase slip line rectifier. This transition is characterized by a strong increase in the rectified voltage and the appearance of a pronounced hysteretic behavior.     

Magneto-photoluminescence study of type-II charge confinement in epitaxially grown GaInP2

We have studied the photoluminescence from GaInP₂ grown by molecular beam epitaxy as a function of laser power, magnetic field and temperature. We show that the single luminescence peak observed in such samples arises from weakly bound (type-II) excitons in which the electrons are localised and the holes are free, and that it is the same as the additional low-energy peak typically observed in strongly CuPt-ordered GaInP₂ grown by chemical vapour deposition techniques. We propose that the electron is confined in In-rich regions of the sample and the hole is delocalised by coupling between heavy- and light-hole bands.     

Confinement in self-assembled InAs/InP quantum wires studied by magneto-photoluminescence

We studied two InAs/InP quantum wire samples with different growth conditions. The photoluminescence of the first sample reveals up to six distinct peaks, while the second has only two pronounced photoluminescence peaks that are attributed to flat wires with heights that differ by exactly one monolayer. Despite the large band offsets in this system, the photoluminescence energy shift of these peaks with a magnetic field applied in the plane of the wires shows that the extent of the exciton wave function in the growth direction is much larger than the wire height, i.e. the wave function spills over into the InP. Moreover, the exciton wave function shrinks for increasing wire height. The wave function spill-over is qualitatively confirmed in the first quantum wire sample.     

Superconductivity in CeCu2Si2

Resistivity measurements of CeCu₂Si₂ are carried out under pressures p up to 12 kbars. Unlike polycrystalline samples, no traces of superconductivity have been observed in CeCu₂Si₂ at ambient pressure. When pressure is applied, CeCu₂Si₂ monocrystals become superconducting with anomalously large ratio H_c2(0)/T_c (0) = 34 K0e/K and with the derivative dH_c2/dT(T=T_c) = 140 K0e/K