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Register a new userSpin current generation and control in carbon nanotubes by combining rotation and magnetic field
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We study the quantum dynamics of ballistic electrons in rotating carbon nanotubes in the presence of a uniform magnetic field. When the field is parallel to the nanotube axis, the rotation-induced electric field brings about the spin-orbit interaction which, together with the kinetic, inertial, and Zeeman terms, compose the Schrodinger-Pauli Hamiltonian of the system. Full diagonalization of this Hamiltonian yields the eigenstates and eigenenergies leading to the calculation of the charge and spin currents. Our main result is the demonstration that, by suitably combining the applied magnetic field intensity and rotation speed, one can tune one of the currents to zero while keeping the other one finite, giving rise to a spin current generator.
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A vortex-antivortex (VA) dipole may be generated due to a spin-polarized current flowing through a nano-aperture in a magnetic element. We study the vortex dipole dynamics using the Landau-Lifshitz equation in the presence of an in-plane applied magnetic field and a Slonczewski spin-torque term with in-plane polarization. We establish that the vortex dipole is set in steady state rotational motion. The frequency of rotation is due to two independent forces: the interaction between the two vortices and the external magnetic field. The nonzero skyrmion number of the dipole is responsible for both forces giving rise to rotational dynamics. The spin-torque acts to stabilize the vortex dipole motion at a definite vortex-antivortex separation distance. We give analytical and numerical results for the angular frequency of rotation and VA dipole features as functions of the parameters.
The interplay between discrete vibrational and electronic degrees of freedom directly influences the chemical and physical properties of molecular systems. This coupling is typically studied through optical methods such as fluorescence, absorption, and Raman spectroscopy. Molecular electronic devices provide new opportunities for exploring vibration-electronic interactions at the single molecule level. For example, electrons injected from a scanning tunneling microscope tip into a metal can excite vibrational excitations of a molecule in the gap between tip and metal. Here we show how current directly injected into a freely suspended individual single-wall carbon nanotube can be used to excite, detect, and control a specific vibrational mode of the molecule. Electrons inelastically tunneling into the nanotube cause a non-equilibrium occupation of the radial breathing mode, leading to both stimulated emission and absorption of phonons by successive electron tunneling events. We exploit this effect to measure a phonon lifetime on the order of 10 nanoseconds, corresponding to a quality factor well over 10000 for this nanomechanical oscillator.
We demonstrate theoretically that an off-resonant circularly polarized electromagnetic field can induce a persistent current in carbon nanotubes, which corresponds to electron rotation about the nanotube axis. As a consequence, the nanotubes acquire magnetic moment along the axis, which depends on their crystal structure and can be detected in state-of-the-art measurements. This effect and related phenomena are analyzed within the developed Floquet theory describing the electronic properties of the nanotubes irradiated by the field.
The spin-orbit coupling (SOC) can mediate electric-dipole spin resonance (EDSR) in an a.c. electric field. In this letter, the EDSR is essentially understood as an spin precession under an effective a.c. magnetic field induced by the SOC in the reference frame, which is exactly following the classical trajectory of the electron and obtained by applying a quantum linear coordinate transformation. With this observation for one-dimensional (1D) case, we find a upper limit for the spin-flipping speed in the EDSR-based control of spin, which is given by the accessible data from the current experiment. For two-dimensional case, the azimuthal dependence of the effective magnetic field can be used to measure the ratio of the Rashba and Dresselhause SOC strengths.
Employing unbiased large-scale time-dependent density-matrix renormalization-group simulations, we demonstrate the generation of a charge-current vortex via spin injection in the Rashba system. The spin current is polarized perpendicular to the system plane and injected from an attached antiferromagnetic spin chain. We discuss the conversion between spin and orbital angular momentum in the current vortex that occurs because of the conservation of the total angular momentum and the spin-orbit interaction. This is in contrast to the spin Hall effect, in which the angular-momentum conservation is violated. Finally, we predict the electromagnetic field that accompanies the vortex with regard to possible future experiments.
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