Observation of sixfold degenerate fermions in a superconducting metal.*

Condensed matter systems offer a unique platform to study fermions from high energy physics. It is well-known that Dirac and Weyl fermions with four- and twofold degeneracy were visualized in topological quantum materials recently. Beyond these fundamental fermions in high energy physics, it has been proposed that crystal and time-reversal symmetries in solids can also protect three-, six- and eightfold degenerate band crossings. These exotic fermions have no high energy analogues due to Poincare invariance. In this talk, I will present our ultrahigh resolution photoemission study on a superconducting metal that hosts three doubly degenerate quadratic bands at the R point, demonstrating a topological fermion beyond the constraints of high energy physics.