Abrikosov vortex contains magnetic field and circulating currents that decay at a short range λ ∼ 100 nm. However, the vortex can induce a long range Josephson phase shift at distances r ∼ µm λ. The mechanism of this puzzling phenomenon is not clearly understood. Here we present a systematic study of vortex-induced phase shift in planar Josephson junctions. We make two key observations: (i) The cutoff effect: although vortexinduce phase shift is a long-range phenomenon, it is terminated by the junction and does not persists beyond it. (ii) A crossover from linear to superlinear dependence of the phase shift on the vortex polar angle occurs upon approaching of the vortex to the junction. The crossover occurs at a distance comparable with the penetration depth. This, together with theoretical and numerical analysis of the problem, allows unambiguous identification of two distinct and independent mechanisms. The short range mechanism is due to circulating vortex currents inside superconducting electrodes without involvement of magnetic field. The long range mechanism is due to stray magnetic fields outside electrodes without circulating vortex currents. We argue that understanding of controlling parameters of vortex-induced Josephson phase shift can be used for development of compact and fast electronic devices with low dissipation power.

We describe the controlled use of a 17 keV X-ray synchrotron nanobeam to progressively change the oxygen doping level in Bi-2212 superconducting whisker-like single crystals. Our data combine structural and electrical information collected on the same crystals, showing a maximum change in the critical temperature Tc of 1.3 K and a maximum elongation of ∼1 Å in the c-axis length, compared to the as-grown conditions. Simulations of our experimental conditions by means of a finite element model exclude local heating induced by the X-ray nanobeam as a possible cause for the change in the doping level and suggest an important role of secondary electrons. These findings support the possible use of hard X-rays as a novel direct-writing, photoresist-free lithographic process for the fabrication of superconducting devices, with potential nanometric resolution and 3D capability.

We describe the first use of a novel photoresist-free X-ray nanopatterning technique to fabricate an electronic device. We have produced a proof-of-concept device consisting of a few Josephson junctions by irradiating microcrystals of the Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide with a 17.6 keV synchrotron nanobeam. Fully functional devices have been obtained by locally turning the material into a nonsuperconducting state by means of hard X-ray exposure. Nano-XRD patterns reveal that the crystallinity is substantially preserved in the irradiated areas that there is no evidence of macroscopic crystal disruption. Indications are that O ions have been removed from the crystals, which could make this technique interesting also for other oxide materials. Direct-write X-ray nanopatterning represents a promising fabrication method exploiting material/material rather than vacuum/material interfaces, with the potential for nanometric resolution, improved mechanical stability, enhanced depth of patterning, and absence of chemical contamination with respect to traditional lithographic techniques.

Josephson current provides a phase sensitive tool for probing the pairing symmetry. Here we present an experimental study of high-quality Josephson junctions between a conventional s-wave superconductor Nb and a multi-band iron-pnictide Ba1−xNaxFe2As2. Junctions exhibit a large enough critical current density to preclude the d-wave symmetry of the order parameter in the pnictide. However, the IcRn product is very small 3 µV, which is not consistent with the sign-preserving s++ symmetry either. We argue that the small IcRn value along with its unusual temperature dependence provide evidence for the sign-reversal s± symmetry of the order parameter in Ba1−xNaxFe2As2. We conclude that it is the phase sensitivity of our junctions that leads to an almost complete (bellow a sub-percent) cancellation of supercurrents from sign-reversal bands in the pnictide.Symmetry of the order parameter provides one of the main clues about the mechanism of superconductivity. Attractive electron-phonon interaction leads to a simple s-wave symmetry in conventional low-T c superconductors. Unconventional superconductivity in cuprates and iron-pnictides is characterized by a proximity to an antiferromagnetic state, suggesting importance of spin interactions. The corresponding direct electron-electron interaction is non-retarded and, therefore, repulsive. It was predicted that this could favor superconductivity with a sign-reversal symmetry [1][2][3]. In single band cuprates the sign-reversal can be only achieved with a d-wave symmetry [1,4]. But in a multi-band pnictides the sign change may also take place between different bands, resulting in the s ± symmetry [2,3,[5][6][7]. On the other hand, presence of the nematic order [8][9][10][11][12][13][14] suggests importance of charge/orbital interactions [15,16], which could lead to a sign-preserving s ++ symmetry [17]. Thus, establishing of the gap symmetry provides a key evidence towards the mechanisms of unconventional superconductivity.At present determination of the gap symmetry in ironpnictides remains ambiguous. For example, a resonant peak observed in inelastic neutron scattering [18][19][20] can be due to either a zero in the denominator of the dynamic spin susceptibility, caused by the sign-reversal order parameter, or to the nominator (Lindhard function) [21], if one takes into account quasiparticle damping [22]. Gap nodes, deduced from angular resolved photoemission spectroscopy [23] and heat conductance [24] may indicate either s ± or d-wave symmetry. Alternatively, the strong reduction of the gap can be related with the change of the orbital character from d xz/yz to d z 2 −1 [25].Josephson effect facilitates phase-sensitive probe of the order parameters [1,[4][5][6][7]. So far few reliable phasesensitive experiments were reported for pnictides [26][27][28][29]. Both integer and half-integer flux-quantum transitions were observed [26] and large variations of the I c R n product, where I c is the critical current and R n is the junction resistance, were reported [27]. Interpretat...