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.

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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