Lecturer: Dr. Karen Michaeli
Affiliation: Weizmann Institute of Science
Abstract:
The functionality of many biological systems
depends on reliable electron transfer with
minimal heating. Unlike man-made electric
circuits, nature realizes electron transport via
insulating chiral molecules. Electron transfer
in cells occurs via tunneling---direct or in
several steps---through organic molecules,
most of which exhibit a helical structure. The
high efficiency of electron transfer in these
systems, especially over distances of
nanometers and beyond, is unexpected for
tunneling-based transport and is one of the
most compelling questions in the field. Recent
experiments have revealed that transport
through such helix-shaped molecules strongly
depend on the electron's spin. Theoretical
attempts to explain this effect rely on large
spin-orbit coupling, which is uncommon in
organic materials. In this talk I will show that
the helical geometry induces correlations
between the spin of the transferred electrons
and their flow direction. In the tunneling
regime, these connections can explain the
large spin polarization measured in
experiments over an energy range of hundreds
of meV, as well as the enhanced transmission
through chiral molecules. The directionality
generated by the locking of the electron spin
and momentum may hold the key to
understanding the extremely low dissipation of
electric transfer through organic molecules
despite strong molecular vibrations.