  Plasmons --the collective oscillations of electrons in conducting materials--
play a pivotal role in nanophotonics because of their ability to couple
electronic and photonic degrees of freedom. In particular, plasmons in graphene
--the atomically thin carbon material-- offer strong spatial confinement and
long lifetimes, accompanied by extraordinary optoelectronic properties derived
from its peculiar electronic band structure. Understandably, this material has
generated great expectations for its application to enhanced integrated
devices. However, an efficient scheme for detecting graphene plasmons remains a
challenge. Here we show that extremely compact graphene nanostructures are
capable of realizing on-chip electrical detection of single plasmons.
Specifically, we predict a twofold increase in the electrical current across a
graphene nanostructure junction caused by the excitation of a single plasmon.
This effect, which is due to the increase in electron temperature following
plasmon decay, should persist during a picosecond time interval characteristic
of electron-gas relaxation. We further show that a broad spectral detection
range is accessible either by electrically doping the junction or by varying
the size of the nanostructure. The proposed graphene plasmometer could find
application as a basic component of future optics-free integrated nanoplasmonic
devices.
