CMSA Condensed Matter/Math Seminar: Supermetal from a high-order Van Hove singularity

A Van Hove singularity (VHS) of the density of states (DOS) is universal in a periodic system.  In two dimensions, a saddle point of energy dispersion yields a logarithmic divergence in the DOS.  Here, we introduce a new kind of VHS, motivated by the recent development of moiré materials.  We define a high-order VHS, which gives a power-law DOS divergence [1].  It requires only a single tuning parameter, such as a twist angle of a moiré material, pressure, and strain.  We further perform a renormalization group analysis near a high-order VHS to study the effect of electron interactions [2].  We reveal a nontrivial metallic state, where various divergent susceptibilities coexist, but no long-range order appears.  We call such a metallic state as a supermetal.  Our controlled analysis shows that a supermetal at the interacting fixed point is a non-Fermi liquid.

[1] N. F. Q. Yuan, H. Isobe, and L. Fu, Nat. Commun. 10, 5769 (2019).
[2] H. Isobe and L. Fu, Phys. Rev. Research 1, 033206 (2019).

via Zoom: https://harvard.zoom.us/j/977347126