Haim Beidenkopf: Generation of High-Order Van Hove Singularity and Pomeranchuk Instability on the Distorted Surface of a Kagome Metal

Haim Beidenkopf

Weizmann Institute of Science

11:30 am - 12:30 pm

Elings Hall 1601

Abstract: The band structure of Kagome metals hosts a flat band and a Dirac node with two saddle points flanking it. Exotic electronic states are spontaneously formed when such high density bands lie in the vicinity of the Fermi energy such as charge density waves. We investigate a Kagome ferromagnetic metal using scanning tunneling spectroscopy. We identify a triangular distortion on its Kagome surface termination that considerably flattens the saddle point dispersion and induces a high-order van Hove singularity pinned to the Fermi energy. The strong interactions of the dense electrons result in a d-wave Pomeranchuck instability. We visualize both in real- and in reciprocalspace a cascade of nematic wavefunction distributions that spontaneously break the rotational symmetry imposed by the underlying distorted Kagome lattice without generating any additional translational symmetry breaking. The evolution of the wave function across the Fermi energy further suggests the spontaneously deformed Fermi surface gives rise to a sort of charge pumping. The form of Kagome distortion that generates the higher order van Hove singularity may be common to other Kagome materials, where it may result in other electronic instabilities.