Symplectic symmetry of quadratic-band-touching Hamiltonians in two dimensions

Igor F. Herbut, Samson C. H. Ling

The internal low-energy symmetry of the massless Lorentz-invariant Dirac Hamiltonian in $2+1$ dimensions is known to be $O(2N)$, where $N$ is the number of two-component Dirac ferm…