Flat band in hole-doped transition metal dichalcogenide observed by angle-resolved photoemission spectroscopy

Layered transition metal dichalcogenides(TMDCs)gained widespread attention because of their electron-correlation-related physics,such as charge density wave(CDW),superconductivity,etc.In this paper,we report the high-resolution angle-resolved photoemission spectroscopy(ARPES)studies on the electronic structure of Ti-doped 1T-TixTa1-xS2 with different doping levels.We observe a flat band that originates from the formation of the star of David super-cell at the x=5％sample at the low temperature.With the increasing Ti doping levels,the flat band vanishes in the x=8％sample due to the extra hole carrier.We also find the band shift and variation of the CDW gap caused by the Ti-doping.Meanwhile,the band folding positions and the CDW vector qCDW are intact.Our ARPES results suggest that the localized flat band and the correlation effect in the 1T-TMDCs could be tuned by changing the filling factor through the doping electron or hole carriers.The Ti-doped 1T-TixTa1-xS2 provides a platform to fine-tune the electronic structure evolution and a new insight into the strongly correlated physics in the TMDC materials.