A Fractional Chiral Semimetal


  Kirill Shtengel  ,  Tobias Meng,  ,  Adolfo G. Grushin  ,  Jens H. Bardarson  
Department of Physics and Astronomy, University of California at Riverside, Riverside, CA 92521, USA

Formulating consistent theories describing strongly correlated metallic topological phases is an outstanding problem in condensed-matter physics. I will present an explicit construction of a fractionalized analog of the Weyl semimetal state: the fractional chiral metal. Our approach is to construct a 4+1D quantum Hall insulator by stacking 3+1D Weyl semimetals in a magnetic field. In a strong enough field, the low-energy physics is determined by the lowest Landau level of each Weyl semimetal, which is highly degenerate and chiral, motivating us to use a coupled-wire approach. In the presence of electron-electron interactions a gapped phase emerges; its electromagnetic response is given in terms of a Chern-Simons field theory. A boundary of this four dimensional phase remains gapless. The boundary's response to an external electromagnetic field is determined by a chiral anomaly with a fractional coefficient. We suggest that such an anomalous response can be taken as a working definition of a fractionalized strongly correlated analog of the Weyl semimetal state