RT Journal Article SR Electronic T1 Filling-enforced quantum band insulators in spin-orbit coupled crystals JF Science Advances JO Sci Adv FD American Association for the Advancement of Science SP e1501782 DO 10.1126/sciadv.1501782 VO 2 IS 4 A1 Po, Hoi Chun A1 Watanabe, Haruki A1 Zaletel, Michael P. A1 Vishwanath, Ashvin YR 2016 UL http://advances.sciencemag.org/content/2/4/e1501782.abstract AB 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.