Fabry-Perot interference and spin filtering in carbon nanotubes
Claudia S. Peca1, Leon Balents1, Kay Jörg Wiese2
1Physics Department, University of California at Santa
Barbara, Santa Barbara, CA 93106-4030, USA
2
KITP, University of California at Santa Barbara, Santa Barbara, CA 93106-4030, USA
Abstract
We study the two-terminal transport properties
of a metallic single-walled carbon nanotube with good contacts to
electrodes, which have recently been shown [W. Liang et al, Nature
441, 665-669 (2001)] to conduct ballistically with weak backscattering
occurring mainly at the two contacts. The measured conductance, as a
function of bias and gate voltages, shows an oscillating pattern of
quantum interference. We show how such patterns can be understood and
calculated, taking into account Luttinger liquid effects resulting
from strong Coulomb interactions in the nanotube. We treat
back-scattering in the contacts perturbatively and use the Keldysh
formalism to treat non-equilibrium effects due to the non-zero bias
voltage. Going beyond current experiments, we include the effects of
possible ferromagnetic polarization of the leads to describe spin
transport in carbon nanotubes. We thereby describe both incoherent
spin injection and coherent resonant spin transport between the two
leads. Spin currents can be produced in both ways, but only the latter
allow this spin current to be controlled using an external gate. In
all cases, the spin currents, charge currents, and magnetization of
the nanotube exhibit components varying quasiperiodically with bias
voltage, approximately as a superposition of periodic interference
oscillations of spin- and charge-carrying ``quasiparticles'' in the
nanotube, each with its own period. The amplitude of the higher-period
signal is largest in single-mode quantum wires, and is somewhat
suppressed in metallic nanotubes due to their sub-band degeneracy.
cond-mat/0304496
[pdf]
Phys. Rev. B 68 (2003) 205423 [pdf]
Copyright (C) by Kay Wiese. Last edited March 17, 2008.