Spintronics of a Nanoelectromechanical Shuttle

Abstract

We consider effects of the spin degree of freedom on the nanomechanics of a single-electron transistor (SET) containing a nanometer-sized metallic cluster suspended between two magnetic leads. It is shown that in such a nanoelectromechanical SET (NEM-SET) the onset of an electromechanical instability leading to cluster vibrations and "shuttle" transport of electrons between the leads can be controlled by an external magnetic field. Different stable regimes of this spintronic NEM-SET operation are analyzed. Two different scenarios for the onset of shuttle vibrations are found.PACS numbers: 85.85.+j, 73.23.HK, 85.35.Be As the downsizing of electronic devices reaches the near molecular scale, the Coulomb forces associated with inhomogeneous charge distributions produced during device operation become comparable with the chemical forces that hold the device together. Consequently, the spatial configuration of a device may well change dynamically during its operation. This inherent feature of nanoelectronics can be turned into an advantage by designing the devices with the mechanical degrees of freedom in mind; this is the scope of nanoelectromechanics and the basis for nanoelectromechanical systems (NEMS) [1].A pronounced nanoelectromechanical phenomenonelectron transport by means of a nanoelectromechanical "shuttle" mechanism -has recently been predicted to occur in certain NEMS systems as a result of a bias voltage-induced nanoelectromechanical instability [2]. The most suitable device for the experimental observation of this phenomenon is a nanoelectromechanical single-electron transistor (NEM-SET). A NEM-SET is a single-electron transistor (SET) with a movable central island whose center-of-mass motion is confined by some potential. Experimental studies of NEM-SET devices can be found in Refs. [3,4,5]. They have also been extensively investigated theoretically [6,7,8,9,10].Another rapidly developing branch of condensed matter physics is spintronics [11], which deals with devices whose functionality depends on the control and manipulation of the spin rather than the charge of electrons. A recent development of great interest in this context is the demonstration of a magnetic hybrid nanostructure consisting of a single C 60 -molecule placed between two ferromagnetic electrodes [12]. The possibility to manipulate the spin of mechanically shuttled electrons in a molecular NEM-SET of this kind brings about an exciting opportunity to trigger nanomechanical vibrations in the THz range by means of a weak external magnetic * Present address: Kavli Institute of Nanoscience, TU Delft, Lorentzweg 1, 2628 CJ Delft, The Netherlands.field much smaller than the magnetic anisotropy fields in the leads. This Letter is devoted to exploring this very phenomenon. We will show that the spin-dependent tunneling of electrons between differently polarized leads results in a strong sensitivity to an external magnetic field of the nanoelectromechanical instability that is responsible for the shuttling. Depending on the magnitude of the...

Electrical transport through a single-electron transistor strongly coupled to an oscillator

“…These "shuttles" have been investigated in great detail. [5][6][7][8][9][10][11][12][13] Another possibility to couple the electrical and mechanical properties of the device is to design the SET such that its capacitive coupling to the gate depends on the displacement of a mechanical oscillator. Thus, mechanical degrees of freedom of the system may strongly influence the currentvoltage characteristics, current noise, and higher cumulants of the current.…”

Current and current fluctuations in quantum shuttles

“…The Wigner representation of the GME has also turned out to be a useful starting point for further analytic work. 26,29,37 These phase-space representations have a simple form in the classical limit: the Wigner representation of a regularly moving harmonic oscillator is an ellipse. On the other hand, irregular motion under the influence of external noise gives rise to a Gaussian probability distribution centered at the origin.…”

Single molecular shuttle-junction: Shot noise and decoherence

“…Based on the coupling between the transport of spin-polarized electrons and the mechanical degrees of freedom of the island, the shuttle instability is predicted to have two stationary domains such as vibronic and shuttling domains depending on the applied electric and magnetic fields, which suggests an extension to spintronics applications. Therefore, the coupling between the spin polarization of the current and the motion of the molecular island center of mass can be used to control the dynamics of the mechanical degrees of freedom using an external magnetic field [64]. The spin-dependent current in the external magnetic field has been recently studied [8,39,40].…”