Observation of flat and weakly dispersing bands in a van der Waals semiconductor Nb3Br8 with breathing kagome lattice

TL;DR

This study combines ARPES and first-principles calculations to reveal flat and weakly dispersing bands in Nb3Br8, a van der Waals breathing kagome lattice material, highlighting its potential for flat band physics and heterostructure applications.

Contribution

It provides the first detailed experimental and theoretical analysis of the electronic structure of Nb3Br8, emphasizing its flat bands and stability in ultrathin form.

Findings

Presence of multiple flat and weakly dispersing bands confirmed by ARPES.

Theoretical calculations attribute these bands to Nb d orbitals.

Ultrathin Nb3Br8 remains stable and suitable for device integration.

Abstract

Niobium halides, Nb3X8 (X = Cl,Br,I), which are predicted two-dimensional magnets, have recently gotten attention due to their breathing kagome geometry. Here, we have studied the electronic structure of Nb3Br8 by using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. ARPES results depict the presence of multiple flat and weakly dispersing bands. These bands are well explained by the theoretical calculations, which show they have Nb d character indicating their origination from the Nb atoms forming the breathing kagome plane. This van der Waals material can be easily thinned down via mechanical exfoliation to the ultrathin limit and such ultrathin samples are stable as depicted from the time-dependent Raman spectroscopy measurements at room temperature. These results demonstrate that Nb3Br8 is an excellent material not only for studying breathing kagome induced flat band physics and its connection with magnetism, but also for heterostructure fabrication for application purposes.