Charge Pumping in Carbon Nanotubes

Abstract

We demonstrate charge pumping in semiconducting carbon nanotubes by a traveling potential wave. From the observation of pumping in the nanotube insulating state we deduce that transport occurs by packets of charge being carried along by the wave. By tuning the potential of a side gate, transport of either electron or hole packets can be realized. Prospects for the realization of nanotube based singleelectron pumps are discussed. DOI: 10.1103/PhysRevLett.95.256802 PACS numbers: 85.35.Kt, 72.50.+b, 73.23.Hk, 73.63.Kv The phenomenon of charge pumping has attracted considerable interest in the last two decades from both fundamental and applied points of view [1][2][3][4][5][6][7][8][9][10]. In pumping, a periodic in time and spatially inhomogeneous external perturbation yields a dc current. If a fixed number n of electrons is transferred during a cycle then the pumping current is quantized in units of ef, where e is the electron charge and f is the perturbation frequency. An important aspect of single-electron pumps is their potential to provide an accurate frequency-current conversion which could close the measurement triangle relating frequency, voltage, and current. Previously, a realization of quantized current I nef has been achieved in two different ways: first, using devices comprising charge islands and controlled by a number of phase-shifted ac signals [3,4,7]; and second, using one-dimensional (1D) channels within a GaAs heterojunction where a surface acoustic wave (SAW) produces traveling potential wells which convey packets of electrons along the channel [5]. In the SAW pumps, transport of charge resembles the pumping of water by an Archimedean screw. When this principle is combined with Coulomb blockade it results in the pumping of a fixed number of electrons n per cycle. For metrological applications, the delivered current should be in the range of 1 nA and at present only the SAW single-electron pumps satisfy this requirement. However, the accuracy of the SAW pumps must be improved significantly for them to find metrological applications.A quantum regime of pumping, in which quantum interference plays a key role, was first described by Thouless [1,2]. In the Thouless mechanism, a traveling periodic perturbation induces minigaps in the spectrum of an electronic system, and when the Fermi level lies in a minigap an integer number of electrons n are transferred during a cycle, resulting in a quantized current flowing without dissipation. From a fundamental physics standpoint, this mechanism represents a new macroscopic quantum phenomenon reminiscent of the quantum Hall effect and of superconductivity. Possible applications of charge pumping are not limited to metrology. For example, the ability of the pumps to control the position of single electrons could be used in various quantum information processing schemes [11,12].Recently it has been pointed out that carbon nanotubes have significant advantages over semiconductor and metallic systems in terms of single-electron pumping [8,9]. The typical Cou...

Optimization of electron pumping by harmonic mixing

“…electron pumping, by external ac-fields has been realized in experiments with quantum dots [1][2][3], nanotubes [4], semiconductor heterostructures [5,6] and a Josephson junction array [7].…”

Nonadiabatic charge pumping in a one-dimensional system of noninteracting electrons by an oscillating potential

“…The phenomenon of charge pumping and rectification by time-dependent potentials applied to certain points in a system has been extensively studied both theoretically and experimentally [32,33,34,35,36,37,38]. The idea of charge pumping is that periodically oscillating potentials can transfer a net charge per cycle between two leads which are at the same chemical potential.…”

Quantum paddlewheel with ultracold atoms in waveguides

“…Theoretical interest in the subject has continued to be strong, expanding its scope to include superconductors [23] and graphene [24] and carbon nanotubes [25,26] in recent years. This sustained interest is particularly remarkable because experimental demonstration of adiabatic charge pumps in normal mesoscopic conductors has stubbornly remained elusive [27,28], although there has been varied success involving spin currents [19], hybrid normal-superconducting systems [23] and carbon nanotubes [26].…”