Tunable spin-polaron state in a singly clamped semiconducting carbon nanotube

Abstract

We consider a semiconducting carbon nanotube (CNT) laying on a ferromagnetic insulating substrate with one end depassing the substrate and suspended over a metallic gate. We assume that the polarised substrate induces an exchange interaction acting as a local magnetic field for the electrons in the non-suspended CNT side. Generalizing the approach of I. Snyman and Yu.V. Nazarov [Phys. Rev. Lett. 108, 076805 (2012)] we show that one can generate electrostatically a tunable spin-polarized polaronic state localized at the bending end of the CNT. We argue that at low temperatures manipulation and detection of the localised quantum spin state is possible. PACS numbers: 85.85.+j, Nanoelectromechanics with suspended carbon nanotubes evolved rapidly in last few years [1][2][3][4][5][6][7]. Recently I. Snyman and Yu.V. Nazarov [8] considered a semiconducting CNT laying on an insulating substrate with one end of it suspended. A metallic gate below both the insulating substrate and the suspended part of the CNT generates an homogeneous electric field (cf. Fig. 1 of Ref.[8]). The mechanical bending of the suspended part of the nanotube induces then a spatial inhomogeneity of the electrostatic potential along the CNT forming a minimum at the deformable end of the wire. The competition between such an electrostatic bending with both the elastic potential of the CNT and the quantum rigidity of the electronic wave function makes the mechanical bending as well as the formation of the localized polaronic state at the movable end of the CNT to occur as a first order phase transition as a function of the electric field. The estimate for the critical field for a realistic experimental set up was predicted in Ref.[8] to be 0.01 V/µm.An impressive effort of the nanoelectronics community is currently deployed to manipulate and exploit the electronic spin degrees of freedom in transport devices (spintronics) [9]. In this context the possibility of magnetic gating, i.e. the use of ferromagnetic leads inducing magnetic exchange fields E ex /µ B (with µ B the Bohr magneton) on the electronic spin is currently actively investigated [10][11][12][13]. More surprisingly such exchange fields can have remarkable consequences also on the dynamics of a nano-mechanical system for which dynamical (shuttle) instabilities, strong spin-polarized currents, and cooling have been predicted [14][15][16] In this paper we show that the system discussed by Snyman and Nazarov [8] in presence of a magnetic dielectric substrate allows the formation of a localized fully polarized polaronic state. The experimentally observed exchange energy E ex (see Ref. [13,14]) turns out to be as large as tens of Kelvins, thus being of the same order of magnitude of the localization energy for an electron in a CNT on the scale of the micrometer. This allows for a high tunability of the polaronic state by means of two electric gates, below the suspended and non-suspendedFIG. 1. Schematic of the system considered: a CNT laying on a magnetic substrate (C) and protruding out of a l...

Sensitivity of mixing-current technique to detect nanomechanical motion

“…[6][7][8] The force sensitivity of the device is then the limiting factor for the sensitivity, and again recent advances showed that it is possible to obtain record force sensing with carbon-nanotube oscillators. 9,10 At the same time nano-mechanical oscillators can be so small that interaction between electronic and mechanical degrees of freedom may lead to new and unexpected phenomena [11][12][13][14][15] like the blockade of the current [16][17][18][19] , cooling [20][21][22] or unusual mechanical response. 23,24 In order to exploit nanomechanical resonators, or to study their properties, detection of mechanical motion is crucial.…”

Thermoelectric Effects in Tunneling of Spin-Polarized Electrons in a Molecular Transistor

“…[33], [34]. It was demonstrated in [35] that the coupling between the spin-carrying and polaronic subsystems results in the appearance of localized quantum states. In [36], the expressions for the charge current both in the shuttling regime and the regime of low-amplitude quantum oscillations were obtained when taking into account the influence of an external magnetic field on tunneling amplitude phase.…”

Numerical Study of Duffing Nonlinearity in the Quantum Dot Embedded Nanomechanical Resonator

“…e linear dynamic description of nanoelectromechanical systems (NEMS) is well understood when the electromechanical coupling is rather weak [1][2][3][4][5][6][7][8][9]; meanwhile, the existence of the nonlinearities induces too many interesting consequences such as the nonlinear dynamic response in the two-dimensional material membranes, the mechanical bistability in the carbon nanotube (CNT)-based resonator, [10][11][12][13], and unusual mechanical response [8,[14][15][16]. e CNT quantum dot embedded resonators have been widely investigated as ultrasensitive detectors and sensors [17][18][19]; the experimental research group reported higher record sensitivity in mass and force sensing [20,21].…”