title: Filling-enforced quantum band insulators in spin-orbit coupled crystals.
abstract: An early triumph of quantum mechanics was the explanation of metallic and insulating behavior based on the filling of electronic bands. A complementary, classical picture of insulators depicts electrons as occupying localized and symmetric Wannier orbitals that resemble atomic orbitals. We report the theoretical discovery of band insulators for which electron filling forbids such an atomic description. We refer to them as filling-enforced quantum band insulators (feQBIs) because their wave functions are associated with an essential degree of quantum entanglement. Like topological insulators, which also do not admit an atomic description, feQBIs need spin-orbit coupling for their realization. However, they do not necessarily support gapless surface states. Instead, the band topology is reflected in the insulating behavior at an unconventional filling. We present tight binding models of feQBIs and show that they only occur in certain nonsymmorphic, body-centered cubic crystals.
authors.affiliation: Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Hoi Chun
authors.initials: HC
authors.lastname: Po
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Haruki
authors.initials: H
authors.lastname: Watanabe
authors.affiliation: Station Q, Microsoft Research, Santa Barbara, CA 93106, USA.
authors.forename: Michael P
authors.identifier: 0000-0002-9297-7024
authors.initials: MP
authors.lastname: Zaletel
authors.affiliation: Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA.; Materials Science Division, Lawrence Berkeley National Laboratories, Berkeley, CA 94720, USA.
authors.forename: Ashvin
authors.initials: A
authors.lastname: Vishwanath
mesh_terms: D003460:Crystallization; D004583:Electrons; D008962:Models, Theoretical; D011789:Quantum Theory
keywords: Quantum mechanics; band insulators