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The electronic evolution of doped Mott insulators has been extensively studied for decades in search of exotic physical phases. The proposed Mott insulator 1T-TaS2 provides an intriguing platform to study the electronic evolution via doping. Here we apply scanning tunneling microscopy (STM) to study the evolution in Ti-doped 1T-TaS2 at different doping levels. The doping Ti atom locally perturbs the electronic and spin state inside the doped star of David and induces a clover-shaped orbital texture at low-doping levels (x < 0.01). The insulator to metal transition occurs around a critical point x = 0.01, in which small metallic and large insulating domains coexist. The clover-shaped orbital texture emerges at a broader energy range, revealing a competition with the electron correlation. It transforms to a disorder-induced Anderson insulating behavior as doping increases. We directly visualize the trapped electrons in dI/dV conductance maps. The comprehensive study of the series of Ti-doped 1T-TaS2 deepens our understanding of the electronic state evolution in a doped strong-correlated system.

Quasiparticle interference (QPI) of the electronic states has been widely applied in scanning tunneling microscopy to analyze the electronic band structure of materials. Single-defect-induced QPI reveals defectdependent interaction between a single atomic defect and electronic states, which deserves special attention. Due to the weak signal of single-defect-induced QPI, the signal-to-noise ratio is relatively low in a standard twodimensional QPI measurement. In this paper, we introduce a projective quasiparticle interference (PQPI) method in which a one-dimensional measurement is taken along high-symmetry directions centered on a specified defect. We apply the PQPI method to the topological nodal-line semimetal ZrSiS. We focus on two special types of atomic defects that scatter the surface and bulk electronic bands. With an enhanced signal-to-noise ratio in PQPI, the energy dispersions are clearly resolved along high-symmetry directions. We discuss the defect-dependent scattering of bulk bands with the nonsymmorphic symmetry-enforced selection rules. Furthermore, an energy shift of the surface floating band is observed, and a branch of energy dispersion (q 6) is resolved. This PQPI method can be applied to other complex materials to explore defect-dependent interactions in the future.

The transition metal dichalcogenides 1T -TaS2 and 1T -TaSe2 have been extensively studied for the complicated correlated electronic properties. The origin of different surface electronic states remains controversial. We apply scanning tunneling microscopy and spectroscopy to restudy the surface electronic state of bulk 1T -TaSe2. Both insulating and metallic states are identified in different areas of the same sample. The insulating state is similar to that in 1T -TaS2, concerning both the dI/dV spectrum and the orbital texture. With further investigations on single-step areas, the discrepancy of electronic states is found to be associated with different stacking orders. The insulating state is most possibly a single layer property, modulated to a metallic state in some particular stacking orders. The metallic spectrum and corresponding stacking orders are dominant in 1T-TaSe2, consistent with the metallic transport measurement. We then reconcile the bulk metallic and surface insulating state in 1T -TaSe2. The rich phenomena in 1T -TaSe2 deepens our understanding of the correlated electronic state on bulk 1T -TaSe2 and 1T -TaS2.

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