Observation of a flat and extended surface state in a topological semimetal

TL;DR

This paper reports the discovery of a highly localized flat surface state, known as a drumhead state, in a topological semimetal BaAl4, using angle-resolved photoemission spectroscopy, highlighting its potential for exploring exotic quantum phases.

Contribution

It provides the first experimental observation and full characterization of a drumhead surface state in BaAl4, establishing it as a platform for topological quantum physics.

Findings

Identification of a flat, localized surface state in BaAl4

The surface state is confined within a bulk Dirac nodal loop

The state exhibits a peak in the density of states

Abstract

A topological flatband, also known as drumhead states, is an ideal platform to drive new exotic topological quantum phases. Using angle-resolved photoemission spectroscopy experiments, we reveal the emergence of a highly localized possible drumhead surface state in a topological semimetal BaAl4 and provide its full energy and momentum space topology. We find that the observed surface state is highly localized in momentum, inside a square-shaped bulk Dirac nodal loop, and in energy, leading to a flat band and a peak in the density of state. These results establish this class of materials as a possible experimental realization of drumhead surface states and provide an important reference for future studies of fundamental physics of topological quantum phase transition.