  Three types of fermions have been extensively studied in topological quantum
materials: Dirac, Weyl, and Majorana fermions. Beyond the fundamental fermions
in high energy physics, exotic fermions are allowed in condensed matter systems
residing in three-, six- or eightfold degenerate band crossings. Here, we use
angle-resolved photoemission spectroscopy to directly visualize
three-doubly-degenerate bands in PdSb$_2$. The ultrahigh energy resolution we
are able to achieve allows for the confirmation of all the sixfold degenerate
bands at the R point, in remarkable consistency with first-principles
calculations. Moreover, we find that this sixfold degenerate crossing has
quadratic dispersion as predicted by theory. Finally, we compare sixfold
degenerate fermions with previously confirmed fermions to demonstrate the
importance of this work: our study indicates a topological fermion beyond the
constraints of high energy physics.
