Observations of plasmarons in a two-dimensional system: Tunneling measurements using time-domain capacitance spectroscopy

Calculations of the single-particle density of states (SPDOS) of electron liquids have long predicted that there exist two distinct charged excitations: the usual quasiparticle consisting of an electron or hole, and a plasmaron consisting of a hole resonantly bound to real plasmons in the Fermi sea. Using tunneling spectroscopy to measure the SPDOS of a 2D electronic system, we demonstrate the detection of a plasmaron in a 2D system in which electrons have mass. With the application of a magnetic field we discover unpredicted magnetoplasmarons which resemble Landau levels with a negative index.