Lifshitz transition and emergence of Van Hove singularity at the complex oxide heterostructure

Electronic correlations strongly depend on the topology of a given electronic structure. A Van Hove singularity (VHS), where the curvature of the electronic bands has opposite sign in two orthogonal directions, is a critical point for a change in electronic topology (Lifshitz transition). It has been considered to be the key to inducing many new unconventional states, especially when it is close to the Fermi level. By using angle-resolved photoemission spectroscopy, we will show the direct evidence of Lifshitz transition and an emergence of VHS in the oxide heterostructures with the different quantum well structures, revealing a new pathway to tune VHS and the corresponding electronic topology at a complex oxide heterointerface.