First direct observation of the Van Hove singularity in the tunneling spectra of cuprates

TL;DR

This paper reports the first direct STM observation of the Van Hove singularity in cuprate superconductors, providing new insights into the electronic structure and pseudogap phase.

Contribution

It presents the first unambiguous STM detection of the Van Hove singularity in cuprates, clarifying longstanding debates about the normal state DOS.

Findings

VHS observed in Bi-2201 via STM

Pseudogap exists on the overdoped side

Discredits pseudogap crossing the superconducting dome

Abstract

In two-dimensional lattices the electronic levels are unevenly spaced, and the density of states (DOS) displays a logarithmic divergence known as the Van Hove singularity (VHS). This is the case in particular for the layered cuprate superconductors. The scanning tunneling microscope (STM) probes the DOS, and is therefore the ideal tool to observe the VHS. No STM study of cuprate superconductors has reported such an observation so far giving rise to a debate about the possibility of observing directly the normal state DOS in the tunneling spectra. In this study, we show for the first time that the VHS is unambiguously observed in STM measurements performed on the cuprate Bi-2201. Beside closing the debate, our analysis proves the presence of the pseudogap in the overdoped side of the phase diagram of Bi-2201 and discredits the scenario of the pseudogap phase crossing the superconducting dome.