Ballistic electron transport and two-level resistance fluctuations in noble-metal nanobridges

Abstract

The electrical properties of microfabricated nanobridges of copper, silver, and gold with contact diameters in the range 4 -32 nm have been studied. High-quality point-contact spectra are evidence that electron transport is ballistic in these nanobridges. A comparison of our spectra with spectra from mechanical point contacts shows that microfabricated nanobridges are at least as good as mechanical point contacts for study of the electron-phonon interaction. Further, in Au nanobridges we have observed defect motion induced two-level resistance fluctuations (TLFs). An expression is derived for the voltage dependence of the temperature Tz of a defect in a nanobridge at low lattice temperatures. Using this expression for Tz, the experimental voltage dependence of the TLF's is successfully described by a thermal-activation model for the fluctuation rates, in which the voltage dependence of the activation energy and defect temperature is included. The values for the attempt time, activation energy, and electromigration parameter are as expected for defects in metals. An analysis of the two TLF's studied, showing a striking difference in both voltage dependence and magnitude of the duty cycle, suggests that rearrangement of complex defects is the mechanism behind the TLF behavior.

Nanoscopic processes of current-induced switching in thin tunnel junctions

“…3. Such behavior can be understood if one considers the expression for the effective barrier modified by electromigration [23] E 0 −ξI, where E 0 is the zero-bias electromigration-energy barrier, ξ is a parameter that measures the change of such activation energy as a result of the electromigration force [24] and I is the applied current. Electromigration then occurs when the effective barrier becomes comparable to the thermal energy.…”

Point-Contact Study of Fast and Slow Two-Level Fluctuators in Metallic Glasses

“…A PC probes only a very small volume (typically ,10 3 nm 3 ), and can therefore be used to study the effect of a few or even a single TLF, present close to the contact area. Beautiful examples of such experiments are observations of two-level resistance fluctuations in clean metallic constrictions caused by lattice defects moving between two metastable configurations [3,4], and of the electromigration of a single defect through a metallic nanoconstruction [5].…”

Potential Fluctuations at Low Temperatures in Mesoscopic-Scale SmTiO3/SrTiO3/SmTiO3 Quantum Well Structures

“…Δ can be calculated. A fluctuating Seebeck coefficient with a microscopic origin of fluctuating chemical potential due to two-level defects [36][37][38] in the etched nanostructures is reasonable in the context of an emerging pseudogap at low T. The pseudogap in these QW structures emerges over the same temperature range as the increase in voltage fluctuations, as T is reduced below 20 K. 18 The transfer of states away from the Fermi level during pseudogap formation and the resulting energy dependence of the density of states is both likely to enhance potential fluctuations due to defects and to enhance the Seebeck coefficient. An analogous response has been observed previously in germanium single crystals, where carrier density fluctuations result in a 1/f noise spectrum of the Seebeck coefficient, even without a dc current.…”