  Ionic Coulomb blockade is one of the mesoscopic effects in ion transport
revealing the quantized nature of ionic charges, which is of crucial importance
to our understanding of the sub-continuum transport in nanofluidics and the
mechanism of biological ion channels. Herein, we report an experimental
observation and plausible theoretical reasoning of ionic conduction
oscillations. Our experiment was performed under strong confinement in single
sub-nanometer MoS2 pores with optoelectronic control enabled for active tuning
of pore surface charges. Under this charge control, we measured the ionic
current at fixed voltages and observed multiple current peaks. Our analytical
discussions and molecular dynamics simulations further reveal that the
conductance oscillations in atomically thin nanopores may originate from the
multi-ion interaction at the pore entry, particularly the electrostatic
repulsion of ions external to the pore by ions bound inside the pore. Our work
adds a further understanding of ionic Coulomb blockade effect under extreme
confinement in atomically thin nanopores and paves the way for developing
advanced ionic machineries.
