Lecturer: Mr. Assaf Hamo
Affiliation:
Department of Condensed-Matter Physics,
Weizmann Institute of Science
Abstract:
One of the defining properties of electrons is
their mutual Coulombic repulsion. In solids,
however, this basic property may change. A
famous example is that of superconductors,
where coupling to lattice vibrations makes
electrons attract each other and leads to the
formation of bound pairs. But what if all
degrees of freedom are electronic? Is it still
possible to make electrons attractive via their
repulsion from other electrons? Such a
mechanism, termed ‘excitonic’, was proposed
fifty years ago by W. A. Little, aiming to
achieve stronger and more exotic
superconductivity, yet despite many
experimental efforts, direct evidence for such
‘excitonic’ attraction is still lacking. Here, we
demonstrate this unique attraction by
constructing, from the bottom up, the
fundamental building block of this
mechanism. Our experiments are based on
quantum devices made from pristine carbon
nanotubes, combined with cryogenic
precision manipulation. Using this platform
we demonstrate that two electrons can be
made to attract using an independent
electronic system as the binding glue. Owing
to its large tunability, our system offers
crucial insights into the underlying physics,
such as the dependence of the emergent
attraction on the underlying repulsion and
the origin of the pairing energy. We also
demonstrate transport signatures of
‘excitonic’ pairing. This experimental
demonstration of ‘excitonic’ pairing paves the
way for the design of exotic states of matter.