  Spin filtering is an essential operation in spintronics that allows creation
and detection of spin polarized carriers. Transition metal ferromagnets are
used as spin filters in most cases, though their spin filtering efficiency is
only around ~50%, thereby limiting the efficiency of spintronic devices.
Recently, chiral systems such as DNA have been shown to exhibit efficient spin
filtering, a phenomenon often dubbed as "chirality induced spin selectivity"
(CISS). In this work, we consider single wall carbon nanotubes helically
wrapped with single stranded poly-T DNA. By magnetoresistance measurements we
show that this system exhibits significant spin polarization of ~80%, which
could be attributed to the Rashba spin-orbit interaction induced by the
inversion asymmetric helical potential of the DNA. Observed spin polarization
is larger than that reported before for d(GT)15 strands. Such systems allow
tailoring spin polarization by chemical means and also allow extremely
localized creation and detection of spin polarization without any magnetic
element and could lead to extreme miniaturization and compact integration of
spintronic devices and circuits.
