Daniel Arovas (Department of Physics, UC San Diego, California)
Band insulators appear in a crystalline system only when the filling – the number of electrons per unit cell and spin projection – is an integer. At fractional filling, an insulating phase that preserves all symmetries is a Mott insulator, i.e. it is either gapless or, if gapped, displays fractionalized excitations and topological order. We raise the inverse question – at an integer filling is a band insulator always possible? Here we show that lattice symmetries may forbid a band insulator even at certain integer fillings, if the crystal is non-symmorphic – a property shared by a majority of three-dimensional crystal structures. In these cases, one may infer the existence of topological order if the ground state is gapped and fully symmetric. This is demonstrated using a non-perturbative flux threading argument, which has immediate applications to quantum spin systems and bosonic insulators in addition to electronic band structures in the absence of spin-orbit interaction.
Reference: Nature Physics 9, 299 (2013)
DÍA: 10 de Octubre (Viernes)
LUGAR: Facultad de Ciencias Físicas, UCM
AULA: Seminario Física Teórica I – 3ª Planta