  Plasmons, quantized collective oscillations of electrons, have been observed
in metals and semiconductors. Such massive electrons have been the basic
ingredients of research in plasmonics and optical metamaterials.1 Also, Dirac
plasmons have been observed in graphene, two-dimensional electron systems and
topological insulators (TIs). A nontrivial Z2 topology of the bulk valence band
leads to the emergence of massless Dirac fermions on the surface in TIs.2,3
Although Dirac plasmons can be formed through additional grating or patterning,
their characteristics promise novel plasmonic metamaterials that are tunable in
the terahertz and mid-infrared frequency ranges.4 Recently, the Majorana
fermions have been verified through various kinds of topological
superconductors(TSCs). In particular, the quantized and paired spin waves have
been discovered in polyaromatic hydrocarbons(PAHs)5 and Majorana hinge and
corner modes have been identified in the organic crystal of PAHs.
Interestingly, regularity and periodicity can serve in the xy-plane of the
crystal as the patterning of TSC resonators. Here, first we report experimental
evidence of Majorana plasmonic excitations in a molecular topological
superconductor (MTSC). It was prepared from MTSC resonators with different
stacked numbers of HYLION-12. Distributing carriers into multiple MTSC
resonators enhance the plasmonic resonance frequency and magnitude, which is
different from the effects in a conventional semiconductor superlattice.6,7 The
direct results of the unique carrier density scaling law of the resonance of
massless Majorana fermions is demonstrated. Moreover, topological surface
plasmon amplification by stimulated emission of radiation (SPASER) is also
firstly created from the MTSC resonator. It has two mutually time-reversed
chiral surface plasmon modes carrying the opposite topological charges.
