We have successfully fabricated Cu/AlOx-Al/Nb normal-metal/insulator/superconductor tunnel junction devices with a high value of the superconducting gap (up to ∼ 1 mV), using electron-beam lithography and angle evaporation techniques in the sub-micron scale. The subgap conductance of these junctions shows the expected strong temperature dependence, rendering them suitable for thermometry all the way from 100 mK to 6 K. In addition, some direct electronic cooling of the normal metal was also seen at bias values near the gap edge. The device performance was strongly influenced by the details of the Al layer geometry, with lateral spilling of the aluminium giving rise to strong extra subgap features, and the thickness of Al layer affecting the proximised superconducting gap value of the superconducting Al/Nb bilayer.Normal-metal-insulator-superconductor (NIS) tunnel junction devices have already proven as promising solid state coolers 1-4 , accurate low temperature thermometers and sensitive bolometers 2,5,6 , and near-ideal single electron transistors 7,8 . Some active research on such devices is aimed at enhancing the cooling power at sub-300 mK temperatures 9 , but increasing the operational range in temperature by changing the superconducting material (gap ∆) from the traditional aluminum has not been very successful yet, although a promising new alternative is to use SIS' structures, instead 10 .To extend the range of NIS devices beyond the operational range of Al, which has an upper limit for thermometry at T C ∼1.5 K and the maximum cooling power at T ∼ 300 mK, one should consider the elemental metal with highest gap, niobium (T C ∼ 9 K). It is already routinely used for SIS tunnel junction applications in SQUIDs, radiation detectors and digital electronics 11 . In those applications, fairly large micron-scale junctions can typically be tolerated, and fabrication usually proceeds by the robust Nb/Al/AlOx/Nb trilayer deposition and etching techniques 12,13 , where Nb and Al are typically sputter deposited, and the high quality AlOx barrier is thermally grown on a thin < 10 nm Al layer. This process typically yields a high gap ∆ ∼ 1.3 mV and a near bulk T C ∼ 9 K 14,15 .In contrast, for single-charge devices and for small thermometers and bolometers, sub-micron scale junctions are desired. They are easier to fabricate using angle-evaporation and lift-off 16 , although a successful but more complex sub-micron Nb trilayer Josephson junction process has also been demonstrated15 . The quality of evaporated Nb, unfortunately, has turned out to be quite sensitive to the exact chamber and substrate conditions, such as vacuum level, evaporation speed, substrate to Nb crucible distance and especially to the type of resist used [17][18][19][20][21][22] . Problems with standard polymer resists are typically attributed to decomposition and outgassing during Nb evaporation, leading to the suppression of T C and ∆.Here, we demonstrate that a fairly simple angleevaporation process can, nevertheless, be used to fabricate good...

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We have successfully fabricated Cu-AlOx-Al-NbN normal metal-insulator-superconductor (NIS) tunnel junction devices, using pulsed laser deposition (PLD) for NbN film growth, and electronbeam lithography and shadow evaporation for the final device fabrication. The subgap conductance of these devices exhibit a strong temperature dependence, rendering them suitable for thermometry from ∼ 0.1 K all the way up to the superconducting transition temperature of the NbN layer, which was here ∼ 11 K, but could be extended up to ∼ 16 K in our PLD chamber. Our data fits well to the single particle NIS tunnel junction theory, with an observed proximised superconducting gap value ∼ 1 meV for a 40 nm thick Al overlayer. Although this high value of the superconducting energy gap is promising for potential electronic NIS cooling applications as well, the high value of the tunneling resistance inhibits electronic cooling in the present devices. Such opaque barriers are, however, ideal for thermometry purposes as self-induced thermal effects are thus minimized.

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In type-II superconductors, increasing applied magnetic field penetrates gradually in the form of magnetic vortices. It is of great interest to understand the dynamics of magnetic flux in different superconducting materials, as this phenomenon can severely limit the performance of superconductors in applications. YBa 2 Cu 3 O 7 − x (YBCO) is an important high-temperature superconductor, but until recently, it has been hard to make wires from it due to misalignment of superconducting grains. A solution to this problem is to deposit YBCO on vicinal substrates to better align the grains. Some of these samples show a strongly intermittent flux penetration at low temperatures. In this work, we have studied flux penetration in YBCO deposited on a 14°vicinal substrate of NdGaO 3 (NGO) at different temperatures.