Observation of flat and weakly dispersing bands in the van der Waals semiconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>Nb</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi>Br</mml:mi></mml:mrow><mml:mn>8</mml:mn></mml:msub></mml:math> with breathing kagome lattice

Niobium halides, ${\mathrm{Nb}}_{3}{X}_{8}$ $(X=\mathrm{Cl},\mathrm{Br},\mathrm{I})$, which are predicted two-dimensional magnets, have recently gotten attention due to their breathing kagome geometry. Here we have studied the electronic structure of ${\mathrm{Nb}}_{3}{\mathrm{Br}}_{8}$ 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 $\mathrm{Nb}\phantom{\rule{0.16em}{0ex}}d$ character indicating their origination from the $\mathrm{Nb}$ 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 ${\mathrm{Nb}}_{3}{\mathrm{Br}}_{8}$ is an excellent material not only for studying breathing kagome induced flat band physics and its connection with magnetism but also for heterostructure fabrication and for practical application.