Spontaneous charge polarization in single-electron tunneling through coupled nanowires

Recent observations of periodic anomalies in conductance of two-dimensional arrays of densely packed metal or semiconductor nanowires give some indication on the importance of collective charge excitations in such systems. These structures can be viewed as parallel arrays of double-tunnel-junction systems with nanowires in the middle which are electrostatically coupled to each other. To assess possible effects of the interwire coupling on the electron transport in such arrays, we investigate the electrical behavior of a simpler system of two coupled double-junction systems under the condition of Coulomb-controlled tunneling. Using Monte Carlo simulations of the electron transport through the system and the master equation analysis, we find that a system of two coupled nanowires exhibits a spontaneous polarization of charge where the accumulation of excessive electrons on one wire is accompanied by the hole accumulation on the neighboring wire. This yields considerable net charge polarization in the transverse direction, which stochastically oscillates in time but depends periodically on the applied voltage, with both the average polarization and the polarization noise decreasing with increasing temperature. The effect gives rise to a number of changes to the well-known Coulomb-Blockade features of a double-junction system, and may lead to the appearance of periodic polarization structures or polarization waves in nanowire arrays which might be detected externally.