Magnetoresistance oscillations of superconducting Al-film cylinders covering InAs nanowires below the quantum critical point.

When odd multiples of half flux quanta thread a cylindrical superconducting shell with a diameter d shorter than the zero temperature coherence length ξ(0), superconductivity is predicted to be destroyed. We show here that as d is reduced in comparison to ξ(0) the resistance attains the normal state value, which seems to be temperature independent in the vicinity of half flux quanta. The data are in agreement with recent theoretical results.

Inverse proximity effect in superconductor-ferromagnet bilayer structures.

Measurements of the polar Kerr effect using a zero-area-loop Sagnac magnetometer on Pb/Ni and Al/(Co-Pd) proximity-effect bilayers show unambiguous evidence for the "inverse proximity effect," in which the ferromagnet induces a finite magnetization in the superconducting layer. To avoid probing the magnetic effects in the ferromagnet, the superconducting layer was prepared much thicker than the light's optical-penetration depth. The sign and size of the effect, as well as its temperature dependence agree with recent predictions by Bergeret et al. [Phys. Rev. B 69, 174504 (2004)]10.1103/PhysRevB.69.174504.

Linear positive magnetoresistance and quantum interference in ferromagnetic metals.

Positive, linear in field, and isotropic magnetoresistance in fields up to 60 T is found in geometrically constrained ferromagnets, such as thin films of iron, nickel, and cobalt and their granular mixtures with nonmagnetic materials. The resistivity measured as a function of temperature shows a minimum at temperatures reaching a remarkably high 92 K, followed by logarithmic dependence at low temperatures. We propose to explain both phenomena by a modified version of the quantum electron-electron interaction theory. The agreement is only qualitative while the observed magnitude of the magnetoresistance slope is much larger than the calculated one.

Luttinger-liquid behavior in weakly disordered quantum wires.

We have measured the temperature dependence of the conductance in long V-groove quantum wires fabricated in GaAs/AlGaAs heterostructures. Our data are consistent with recent theories developed within the framework of the Luttinger-liquid model, in the limit of weakly disordered wires. We show that, for the relatively low level of disorder in our quantum wires, the value of the interaction parameter g congruent with 0.66, which is the expected value for GaAs. However, samples with a higher level of disorder show conductance with stronger temperature dependence, which does not allow their treatment in the framework of perturbation theory. Fitting such data with perturbation-theory models leads inevitably to wrong (lower) values of g.

Oscillations of the superconducting critical current in Nb-Cu-Ni-Cu-Nb junctions.

We report on experimental studies of superconductor-ferromagnet layered structures. Strong oscillations of the critical supercurrent were observed with the thickness variation of the ferromagnet. Using known microscopic parameters of Ni, we found reasonable agreement between the period of oscillations and the decay of the measured critical current, and theoretical calculations.