Experimental evidence for the Coulomb blockade of Cooper pair tunneling and Bloch oscillations in single Josephson junctions

We report on measurements of the current-voltage characteristics of ultrasmall Josephson junctions. The junctions were made of either Al or Pb alloy, and the leads connecting the junctions to the outside world were high resistance thin film microstrips fabricated on the chip very close to the junction. The high frequency impedance of these leads was sufficiently large to enable the observation in a single Josephson junction of the Coulomb blockade of Cooper pair tunneling, as well as evidence for the time correlation of Cooper pair tunneling (Bloch Oscillations).     

Dielectric response of Ba0.75Sr0.25TiO3 epitaxial films to electric field and temperature

The structure and dielectric parameters of the intermediate ferroelectric layer in the (001)SrRuO₃ ∥ (100)Ba_0.75Sr_0.25TiO₃ ∥ (001)SrRO₃ heterostructure grown by laser ablation on (001)La_0.294Sr_0.706Al_0.647Ta_0.353O₃ were studied. Tensile mechanical stresses accounted for the polar axis in the ferroelectric, being oriented predominantly parallel to the substrate plane. The remanent polarization in the Ba_0.75Sr_0.25TiO₃ layer increased approximately linearly with decreasing temperature in the interval 320–200 K. The real part of the dielectric permittivity of the intermediate ferroelectric layer reached a maximum ?′/?₀=4400 at T _M≈285 K (f=100 kHz). The narrow peak in the temperature dependence of the dielectric loss tangent for the Ba_0.75Sr_0.25TiO₃ ferroelectric layer, observed for T<T _M, shifted toward lower temperatures with decreasing frequency and increasing bias voltage applied to the electrodes.     

Localized phonons in thallium-indium by superconductive tunneling

Phonon induced structure in superconductive tunneling curves indicates the existence of localized modes due to light In impurity atoms dissolved in Tl. Their frequencies are higher than the cut-off phonon frequency in pure Tl but slightly lower than expected from mass-defect theory.     

Search for superconductivity in vapour quenched alkaline earth metals and lanthanides

Recent papers by Reale [1–3] report superconducting transitions in vapour quenched films of several alkali-, alkaline earth-, and rare earth metals which were not previously known to be superconducting. We report here a vain effort to verify that Mg, Ba, Ce, Pr, Nd or Yb are superconducting above 0.3 K.Supported by the Swedish National Science Research Council     

Proximity effect in superconducting contacts by electron tunnelling

The excitation spectrum in superconducting lead in the presence of a metallic contact has been investigated. Conductance versus voltage curves disagree with those computed from the BCS theory but agree much better with curves calculated from a depairing theory. The experiments demonstrate the existence of a pair breaking mechanism induced by metallic contact. Tunnelling into the normal side of the double layer gave less conclusive results. Due to a pair enhancing effect, superconductivity exists in the otherwise normal metal, but it cannot be described by the simple BCS picture. A somewhat complicated temperature dependence was registered for the sharpness of the conductance versus voltage curves.     

Pair-breaking in thin superconducting films — the effects on Tc and fluctuation conductivity

The thickness dependent pair breaking parameter, inherent in the Maki-Thompson contribution to the excess conductivity due to superconducting fluctuations, is found to be equal to the observed shift of T_c relative to the bulk value. Measurements were performed on thin amorphous Be_0.7Al_0.3 films produced by vapour quenching.