Chiral charge density waves induced by Ti-doping in 1T-TaS₂

We investigate the Ti-doping effect on the charge density wave (CDW) of 1T-TaS₂ by combining scanning tunneling microscopy measurements and first-principle calculations. Although the Ti-doping induced phase evolution seems regular with an increase of the doping concentration (x), an unexpected chiral CDW phase is observed in the sample with x = 0.08, in which Ti atoms almost fully occupy the central Ta atoms in the CDW clusters. The emergence of the chiral CDW is proposed to be from the doping-enhanced orbital order. Only when x = 0.08, the possible long-range orbital order can trigger the chiral CDW phase. Compared with other 3d-elements doped 1T-TaS₂, the Ti-doping retains the electronic flatband and the corresponding CDW phase, which is a prerequisite for the emergence of chirality. We expect that introducing elements with a strong orbital character may induce a chiral charge order in a broad class of CDW systems. The present results open up another avenue for further exploring the chiral CDW materials.