RESUMO
We present high-resolution conductance measurements in niobium nanowires below the superconducting transition temperature. During elongation we find a bistability region manifesting itself as random telegraph noise. Density functional structural optimizations and conductance calculations reproduce and explain the measurements. In particular, the observed bistability is associated with the formation of a niobium dimer between the opposing electrodes, with the dimer shuttling between a symmetric, high conductance, and an asymmetric, low-conductance configurations in the gap.
RESUMO
In 1962, Josephson made a celebrated prediction: when a constant voltage is applied across a thin insulator separating two superconductors, it will generate an oscillating current. These oscillations are ubiquitous in superconducting weak links of various geometries, and analogues have been found in other macroscopic quantum systems, such as superfluids and gaseous Bose-Einstein condensates. The interplay between the oscillating current and external microwave radiation of matching frequency (Shapiro steps) or with internal electrodynamic resonances (Fiske effect) appear as changes in the current-voltage characteristics of superconducting tunnel junctions and provide further insight into the phenomenon. Here, we report measurements and theoretical studies suggesting that Josephson current oscillations interact with atomic-scale mechanical motion as well. We formed a niobium dimer nanowire that acts as a weak link between two superconducting (bulk) niobium electrodes. We find features in the differential conductance through the dimer which we believe correspond to excitations of the dimer vibrational modes by Josephson oscillations and support our results with theoretical simulations.
Assuntos
Instalação Elétrica/instrumentação , Eletricidade , Microeletrodos , Modelos Químicos , Nanotubos/química , Nióbio/química , Oscilometria/instrumentação , Simulação por Computador , Condutividade Elétrica , Transporte de Elétrons , Desenho de Equipamento , Teste de Materiais , Nanotubos/ultraestrutura , VibraçãoRESUMO
Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.