Increasing the operating frequency of SIS receivers requires a shift from Nb Al AlO X Nb junctions to new material systems. Two major limiting factors of higher frequency operation are the increase in subgap leakage that occurs in AlO X barriers as current densities approach and exceed 10 kA cm 2 and the increased loss in Nb electrodes above 700 GHz. A promising alternative structure is the hybrid Nb/Al-AlN/NbTiN junction. Realization of these devices has been difficult due to the challenge of fabricating devices with repeatable current densities and electrical characteristics.We present on the fabrication and dc testing of Nb/AlN/NbTiN junctions. The AlN barrier is formed using our inductively coupled plasma (ICP) technique which allows for independent control of both ion energy and current density. This improved control enables the repeatable synthesis of high quality and high Jc barriers. Nb and NbTiN electrodes are deposited by unbalanced dc magnetron. A new fabrication process was developed to enable fabrication of junctions with area as small as 0.28 m 2 . The relationship between barrier thickness and plasma conditions is determined by in-situ discrete ellipsometry. Ellipsometry results were verified by comparison with measured current-voltage characteristics. I(V) curves for a range of junction sizes are presented. Plans for in-situ Faraday monitoring of the energy and current density of the ICP nitridation plasma will also be discussed.Index Terms-Aluminum nitride, inductively couple plasma, niobium titanium nitride, SIS.
Carbon nanotubes provide one of the most accessible experimental realizations of one dimensional electron systems. In the experimentally relevant regime of low doping the Luttinger liquid formed by electrons may be approximated by a Wigner crystal. The crystal-like electronic order suggests that nanotubes exhibit effects similar to the Mössbauer effect where the momentum of an emitted photon is absorbed by the whole crystal. We show that the circular photovoltaic effect in chiral nanotubes is of the same nature. We obtain the frequency dependence of the photovoltage and characterize its singularities in a broad frequency range where the electron correlations are essential. Our predictions provide a basis for using the photogalvanic effect as a new experimental probe of electron correlations in nanotubes.
The conductance through a semi-infinite one-dimensional wire, partly embedded in a superconducting bulk electrode, is studied. When the electron-electron interactions within the wire are strongly repulsive, the wire effectively decouples from the superconductor. If they are moderately or weakly repulsive, the proximity of the superconductor induces superconducting order in the segment of the wire embedded in it. In this case it is shown that the conductance exhibits a crossover from conductive to insulating behavior as the temperature is lowered down. The characteristic crossover temperature of this transition has a stretched exponential dependence on the length of the part of the wire embedded in the superconductor. The amount of this stretch is determined by the nature of the electron interactions within the wire.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.