We report superconducting phase-periodic conductance oscillations in ferromagnetic wires with interfaces to conventional superconductors. The ferromagnetic wires were made of Ho, a conical ferromagnet. The distance between the interfaces was much larger than the singlet superconducting penetration depth. We explain the observed oscillations as due to the long-range penetration of an unusual helical triplet component of the order parameter that is generated at the superconductor/ferromagnet interfaces and maintained by the intrinsic rotating magnetization of Ho.

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A strong mutual influence of superconductors (S) and ferromagnetic (F) conductors in hybrid F͞S (Ni͞Al) nanostructures is observed. The proximity-induced conductance on the F side, DG, is 2 orders of magnitude larger than that predicted by theory. A crossover from positive to negative DG takes place upon an increase in the F͞S interface barrier resistance. Reentrance of the superconductors to the normal state reciprocated by changes on the F side has been found in low applied magnetic fields with new peaks in the differential resistance as an effect of the saturation magnetization. An analysis has been developed providing a base for a numerical description of the system.

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We report measurements of thermopower oscillations vs magnetic field in a diffusive Andreev interferometer. Upon the increase of the dc current applied to the heater electrodes, the amplitude of these oscillations first increases then goes to zero as one would expect. Surprisingly, the oscillations reappear at yet higher heater currents with their phase being π-shifted compared to low current values. From direct measurements of the temperature gradient we estimate the amplitude of the oscillations to be orders of magnitude smaller than predicted by theory.In a nonuniformly heated conductor there arises an electric field, E, proportional to the temperature gradient E = Q∇T , where Q is known as thermopower. In metals Q is determined [1] by a derivative of the logarithm of conductivity σ with respect to energy ε taken at the Fermi levelwhere k B is Boltzman constant and e is electron charge. In normal metals with diffusive electron transport the conductivity changes very little with energy and the thermopower has the following order of magnitudewhere C is a constant of the order of unity depending on the topology of Fermi surface and the energy dependence of scattering time.The thermoelectric properties of a normal metal (N ) in contact with a superconductor (S) are strongly modified by the proximity effect. First, the electrical conductivity has a much stronger energy dependence, so that the thermopower can be orders of magnitude larger than predicted by Eq. (2) [2]. In the geometry of Andreev interferometer, when the normal part is connected to the superconducting loop, the thermopower will oscillate as a function of the magnetic flux Φ through the loop, with a period equal to the flux quantum Φ 0 = hc/2e. It was shown that these oscillations can be symmetric or antisymmetric with respect to Φ depending on the sample topology in contrast to the conductance oscillations which are always symmetric [2]. Second, the voltage between N and S circuits may appear due to nonequilibrium branch imbalance in the N film created by temperature gradient [3]. The thermopower associated with this effect is predicted to be giant compared with Eq. (2) as it does not contain small factor k B T /ε F . The thermopower oscillations are predicted to be close to antisymmetric in this case [3].Recently, the oscillating thermovoltage of mesoscopic (Au/Al) Andreev interferometer has been discovered in a pioneering experiment by Chandrasekhar's group [4]. The value of Q was estimated to be consistent with theoretical predictions [2]. For various geometries of Andreev interferometer, both symmetric and antisymmetric oscillations were observed. Later experiments by the same group with direct measurements of temperature gradients proved that the thermopower was indeed orders of magnitude larger than (2) [5]. The origin of the phase of thermopower oscillations for different geometries is still unclear.In this Letter we report measurements of thermopower oscillations vs magnetic field in a (Sb/Al) Andreev interferometer. As a function of heater c...