Topological semimetal: a probable new state of quantum optical lattice gases protected by D$_4$ symmetry

ORAL

Abstract

We demonstrate that a novel topological semimetal emerges as a parity-protected critical theory for fermionic atoms loaded in the $p$ and $d$ orbital bands of a two-dimensional optical lattice. The new quantum state is characterized by a parabolic band-degeneracy point with Berry flux $2 \pi$, in sharp contrast to the $\pi$ flux of Dirac points as in graphene. We prove that this topological liquid is a universal property for all lattices of D$_4$ point group symmetry and the band degeneracy is protected by odd parity. Turning on interparticle repulsive interaction, the system undergoes a phase transition to a topological insulator, whose experimental signature includes chiral gapless domain-wall modes, reminiscent of quantum Hall edge states.

*KS and SDS acknowledge the support of JQI-NSF-PFC, AFOSR-MURI, ARO-DARPA-OLE and ARO-MURI. W.V.L. is supported by ARO and ARO-DARPA-OLE. We thank the KITP at UCSB for its hospitality where this research is supported in part by NSF Grant No. PHY05-51164.

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Authors

  • Kai Sun

    • University of Maryland
    • Joint Quantum Institute and Condensed Matter Theory Center, University of Maryland, College Park, MD 20742
    • JQI and CMTC, University Of Maryland

  • W. Vincent Liu

    • University of Pittsburgh
    • University of Pittsburgh and Kavli Institute for Theoretical Physics, University of California, Santa Barbara
    • University of Pittsburgh and KITP UCSB

  • Sankar Das Sarma

    • Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, MD 20742
    • Condensed Matter Theory Center, Department of Physics, University of Maryland
    • Univ of Maryland-College Park
    • Condensed Matter Theory Center, Dept. of Physics, University of Maryland, College Park, MD
    • CMTC, Dept of Physics, University of Maryland, College Park
    • Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
    • Condensed Matter Theory Center, University of Maryland, College Park
    • Dep. of Physics, Condensed Matter Theory Center, University of Maryland, College Park, Maryland
    • University of Maryland
    • JQI and CMTC, University of Maryland
    • Joint Quantum Institute and Condensed Matter Theory Center, University of Maryland