We have studied electron tunneling in ultralow-capacitance silver particles sandwiched between artificial tunnel barriers. We have observed steps in the current-voltage characteristics of these systems with voltage widths of e/C (C being the capacitance of the particles), and associated current rises of e/RC. This represents the first observation of the so-called Coulomb staircase, expected for the charging of particles with extremely small capacitance by a discrete number of electrons.PACS numbers: 73.40. Gk, 36.40.+d Very recently, excitement has been generated by the realization that with currently developed materialspreparation techniques, it should be possible to observe the charging of metal particles by a small and countable number of electrons. Indeed, by employing recently developed techniques for the preparation of artificial electron tunnel barriers, we have performed tunneling studies of Ag particles sandwiched between these barriers in structures of the form metal/barrier/particles/ barrier/metal, wherein such effects have been observed. We discuss in this Letter tunneling measurements which reveal clear, periodic modulations of the dc and ac conductance as a function of voltage corresponding to the occupation of ultralow-capacitance silver particles by discrete numbers of electrons.Begun originally by Giaever and Zeller 1 to see whether superconductivity would persist in dimensionally restricted samples, the study of tunneling in small metal particles has been of continual interest because of the myriad outstanding questions regarding the nature of conductors on an ultrasmall scale. Recently, tunneling in small-particle and granular systems has been employed as a natural means of studying Coulomb and localization effects, which tend to be amplified in such systems. The subject has been approached from the standpoint of temperature and finite-frequency effects theoretically by Ho 2 and experimentally by Cavicchi and Silsbee 3 by means of tunnel-capacitor structures of the type originally described by Lambe and Jaklevic. 4 Transport measurements have also been made by Raven 5 in small-particle systems, and tunneling investigations have been performed by White, Dynes, and Garno 6 in granular materials, the latter in conjunction with the study of localization and interaction effects.The goal of the present work is the direct observation of the charging of particles by small, countable numbers of electrons. To accomplish this, we performed tunneling measurements of ultralow-capacitance (< 10 ~1 7 F) Ag particles wherein the charging voltage corresponding to a single electron, e/C, is in an easily measurable range (> 10" 2 V).The systems studied consist of structures containing a layer of isolated Ag particles sandwiched between welldefined artificial tunnel barriers. These systems were prepared by the layer-by-layer deposition of thin films as follows: base electrode/barrier/particles/barrier/counterelectrode. The barriers consist of sputter-deposited AI2O3 films in the 25-to 40-A thickness range. As ...

Recent comparative studies of quasiparticle injection from colossal magnetoresistance (CMR) materials and normal metals into high transition temperature superconductors (HTS) have led several investigators to conclude that spin-polarized injection from CMR electrodes is far more efficient than ordinary injection in suppressing superconductivity. On the other hand, some ordinary quasiparticle injection experiments have shown greater suppression of superconductivity than was claimed in any of the published spin-injection experiments. Careful analysis and numerical simulations lead us to argue that all spin-injection experiments to date have been hampered by inadequate control samples and that the reported results can be explained by ordinary (unpolarized) quasiparticle injection or simple current summation. We conclude that there is no conclusive evidence that spin-polarized injection into HTS behaves differently from ordinary quasiparticle injection and we discuss criteria for future experiments that could differentiate between the two types of injection.

We have demonstrated the controllable, reproducible fabrication of nonhysteretic Josephson devices with excess-current weak-link characteristics at temperatures up to 80 K. The devices are patterned from in situ deposited a-axis oriented YBa2Cu3O7−y-PrBa2Cu3O7−z-YBa2Cu3O7−y trilayers grown on SrTiO3(001) substrates. Control of the critical current density and resistance is achieved by varying the thickness of the PrBa2Cu3O7−z barrier layer. Critical current densities in excess of 104 A/cm2 have been reproducibly measured; good uniformity across the wafer is obtained with device parameters scaling with device area. Strong constant-voltage current steps are observed under 11.2 GHz microwave radiation at temperatures up to and above 80 K.

The epitaxy of a thin-film Y-Ba-Cu-O (YBCO) superconductor deposited on a single-crystal [001] MgO substrate was examined by transmission electron microscopy. The large lattice mismatch (8–10%) in the basal plane of YBCO and MgO is accommodated mainly by the formation of a polycrystalline, mosaic structure. The grain boundaries correspond to unique crystallographic interfaces, determined by the crystal symmetry of the substrate and the thin film.