Schedule Oct 12, 2012
Topological Orbital Ladder
Vincent Liu (Univ. Pittsburgh)

Authors: Xiaopeng Li (University of Pittsburgh), Erhai Zhao (George Mason University), W. Vincent Liu (University of Pittsburgh)

Synthetic quantum matter exploiting the orbital degrees of freedom, such as the recent double-well optical lattices loaded with s and p orbital ultracold atoms, opens an avenue towards exploiting symmetries beyond natural crystals. Observations of exotic superfluidity were reported for bosons.  We unveil a topological phase of interacting fermions on a two-leg ladder of orbitals with unequal parity,  derived from the experimentally realized double-well lattices by dimension reduction. The topological invariant originates from the staggered phases of sp-orbital quantum tunneling, not requiring previously known mechanisms such as spin-orbit coupling, p-wave triplet pairing, artificial gauge field, or rotation.  Another unique feature is that upon crossing over to two dimensions with coupled ladders, the edge modes from each ladder form a parity-protected flat band at zero energy. Experimental signatures are found in density correlations and phase transitions to trivial band and Mott insulators. Acknowledge support by U.S. ARO, AFOSR, and DARPA and A. Mellon Foundation.

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