Exceptional van Hove Singularities in Pseudogapped Metals

TL;DR

This paper introduces the concept of exceptional van Hove singularities in strongly interacting pseudogapped metals, revealing their role in Lifshitz transitions and associated experimental signatures in cuprates.

Contribution

It proposes a new type of van Hove singularity caused by electron interactions, linking it to pseudogap phenomena and experimental observations in cuprate superconductors.

Findings

Exceptional van Hove singularities occur when Fermi surface pieces touch due to interactions.

The singularity is near a second order van Hove point accessible by tuning dispersion.

Enhanced specific heat and nematic susceptibility are observed near the transition.

Abstract

Motivated by the pseudogap state of the cuprates, we introduce the concept of an "exceptional" van Hove singularity that appears when strong electron-electron interaction splits an otherwise simply connected Fermi surface into multiply connected pieces. The singularity describes the touching of two pieces of the split Fermi surface. We show that this singularity is proximate to a second order van Hove singularity, which can be accessed by tuning a dispersion parameter. We argue that, in a wide class of cuprates, the end-point of the pseudogap is accessed only by triggering the exceptional van Hove singularity. The resulting Lifshitz transition is characterized by enhanced specific heat and nematic susceptibility, as seen in experiments.