  The use of an asymmetric broadening in the transport distribution, a
characteristic of resonant structures, is proposed as a route to engineer a
decrease in electronic thermal conductivity thereby enhancing the electronic
figure of merit in nanostructured thermoelectrics. Using toy models, we first
demonstrate that a decrease in thermal conductivity resulting from such an
asymmetric broadening may indeed lead to an electronic figure of merit well in
excess of 1000 in an idealized situation and in excess of 10 in a realistic
situation. We then substantiate with realistic resonant structures designed
using graphene nano-ribbons by employing a tight binding framework with edge
correction that match density functional theory calculations under the local
density approximation. The calculated figure of merit exceeding 10 in such
realistic structures further reinforces the concept and sets a promising
direction to use nano-ribbon structures to engineer a favorable decrease in the
electronic thermal conductivity.
