Observation of type-II and type-III Dirac points in circuit lattices.

Abstract

Dirac fermions are low-energy quasi-particle excitations found in Dirac materials, with their band crossings referred to as Dirac points (DPs). Unlike type-I DPs, type-II, and type-III DPs have attracted significant attention due to their unique magneto-transport properties in condensed matter materials. However, type-II and type-III Dirac materials are notably rare and realizing DPs in macroscopic classical systems presents challenges because of the complex sample fabrication required for mirror symmetry. Here, we report the experimental observation of type-II and type-III DPs in circuit lattices. We confirm the presence of type-II DPs by observing strongly tilted Dirac cones. By varying the coupling capacitors, we demonstrate a transition from type-II DPs to type-III DPs, with the latter characterized by a flat band. Additionally, edge states emerge from the degeneracies associated with both type-II and type-III DPs. Our findings offer valuable insights into novel quantum phenomena in condensed matter materials, including anisotropic magneto-transport and topological phase transitions.