Interaction-driven insulators with topologically distinct properties on the kagome lattice

Date

Apr 6, 2011

Time

2:00 PM - 3:00 PM

Speaker

Andreas Ruegg

Affiliation

Austin - USA

Language

en

Main Topic

Physik

Other Topics

Physik

Host

Condensed Matter Seminar

Description

In this talk, I will discuss gapped phases of interacting fermions on the kagome lattice realized by the spontaneous breaking of a symmetry. In the first part, I show that even in the absence of spin-orbit coupling or external magnetic fields insulating phases with nontrivial topological band invariants (Chern number or Z2 invariant) and protected edge modes exists. The competition between these interaction-driven topological insulators and other ordered states (including various charge, spin and bond orderings) is investigated and mean-field phase diagrams are presented. In the second part, I focus on the charge-density wave which is stabilized at filling fraction f=1/3. The topologically distinct property of this phase manifests itself by the fact that topological point defects in the order parameter lead to isolated midgap states binding a fractional Fermion number. For spin-polarized fermions, the value of the bound charge is 1/2 and protected by inversion symmetry. Breaking this symmetry allows to continuously change the value of the bound charge. Moreover, we compute the confinement potential between two fractionally charged defects and argue that the polaron state, formed upon doping the charge-density wave, can be viewed as a bound state of two defects.

Last modified: Apr 6, 2011, 9:36:19 AM