title: Beyond Dirac and Weyl fermions: Unconventional quasiparticles in conventional crystals.
abstract: In quantum field theory, we learn that fermions come in three varieties: Majorana, Weyl, and Dirac. Here, we show that in solid-state systems this classification is incomplete, and we find several additional types of crystal symmetry-protected free fermionic excitations. We exhaustively classify linear and quadratic three-, six-, and eight-band crossings stabilized by space group symmetries in solid-state systems with spin-orbit coupling and time-reversal symmetry. Several distinct types of fermions arise, differentiated by their degeneracies at and along high-symmetry points, lines, and surfaces. Some notable consequences of these fermions are the presence of Fermi arcs in non-Weyl systems and the existence of Dirac lines. Ab initio calculations identify a number of materials that realize these exotic fermions close to the Fermi level.
authors.affiliation: Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Barry
authors.initials: B
authors.lastname: Bradlyn
authors.affiliation: Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Cano
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San Sebastián, Spain.
authors.forename: M G
authors.initials: MG
authors.lastname: Vergniory
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Felser
authors.affiliation: Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Cava
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA. bernevig@princeton.edu.
authors.forename: B Andrei
authors.initials: BA
authors.lastname: Bernevig