  High spin polarization materials or spin filters are key components in
spintronics, a niche subfield of electronics where carrier spins play a
functional role. Carrier transmission through these materials is "spin
selective" i.e. these materials are able to discriminate between "up" and
"down" spins. Common spin filters include transition metal ferromagnets and
their alloys, with typical spin selectivity (or, polarization) ~50% or less.
Here we consider carrier transport in an archetypical one-dimensional molecular
hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by
single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance
measurements we show that this system can act as a spin filter with maximum
spin polarization approaching ~74% at low temperatures, significantly larger
than transition metals under comparable conditions. Inversion asymmetric
helicoidal potential of the charged ssDNA backbone induces a Rashba spin-orbit
interaction in the SWCNT channel and polarizes carrier spins. Our results are
consistent with recent theoretical work that predicted spin dependent
conductance in ssDNA-SWCNT hybrid. Ability to generate highly spin polarized
carriers using molecular functionalization can lead to magnet-less and
contact-less spintronic devices in the future. This can eliminate the
conductivity mismatch problem and open new directions for research in organic
spintronics.
