Charge density wave (CDW) is a phenomenon that occurs in materials, accompanied by changes in their intrinsic electronic properties. The study of CDW and its modulation in materials holds tremendous significance in materials research, as it provides a unique approach to controlling the electronic properties of materials. TiSe₂ is a typical layered material with a CDW phase at low temperatures. Through V substitution for Ti in TiSe₂, we tuned the carrier concentration in V_xTi_1−xSe₂ to study how its electronic structures evolve. Angle-resolved photoemission spectroscopy (ARPES) shows that the band-folding effect is sustained with the doping level up to 10%, indicating the persistence of the CDW phase, even though the band structure is strikingly different from that of the parent compound TiSe₂. Though CDW can induce the band fold effect with a driving force from the perspective of electronic systems, our studies suggest that this behavior could be maintained by lattice distortion of the CDW phase, even if band structures deviate from the electron-driven CDW scenario. Our work provides a constraint for understanding the CDW mechanism in TiSe₂, and highlights the role of lattice distortion in the band-folding effect.

Taking advantage of the unique layered structure of TiSe₂, the intrinsic electronic properties of two-dimensional materials can easily be tuned via heteroatomic engineering. Herein, we show that the charge density wave (CDW) phase in 1T-TiSe₂ single-crystals can be gradually suppressed through Sn atoms intercalation. Using angle-resolved photoemission spectroscopy (ARPES) and temperature-dependent resistivity measurements, this work reveals that Sn atoms can induce charge doping and modulate the intrinsic electronic properties in the host 1T-TiSe_2. Notably, our temperature-dependent ARPES results highlight the role exciton-phonon interaction and the Jahn-Teller mechanism through the formation of backfolded bands and exhibition of a downward Se shift of 4p valence band in the formation of CDW in this material.

The intercalation of metal is a promising method for the modulating electronic properties in transition metal dichalcogenides (TMDs). However, there still lacks enough knowledge about how the intercalated atoms directly impact the two-dimensional structural layers and modulate the band structures therein. Taking advantage of X-ray absorption fine structure and angle-resolved photoemission spectroscopy, we studied how Cu intercalation influences the host TaSe₂ layers in Cu_0.03TaSe₂ crystals. The intercalated Cu atoms form bonds with Se of the host layers, and there is charge transfer from Cu to Se. By examining the changes of band dispersions, we show that the variation of electronic structures is beyond a simple rigid band model with merely charge doping effect. This work reveals that the unusual change of band dispersions is associated with the formation of bonds between the intercalated metal elements and anion ions in the host layers, and provides a reference for the comprehensive understanding of the electronic structures in intercalated materials.

Atomic intercalation in two-dimensional (2D) layered materials can be used to engineer the electronic structure at the atomic scale and generate tuneable physical and chemical properties which are quite distinct in comparison with the pristine material. Among them, electron-doped engineering induced by intercalation is an efficient route to modulate electronic states in 2D layers. Herein, we demonstrate a semiconducting to metallic phase transition in zirconium diselenide (ZrSe₂) single crystals via controllable incorporation of copper (Cu) atoms. Our angle resolved photoemission spectroscopy (ARPES) measurements and first-principles density functional theory (DFT) calculations clearly revealed the emergence of conduction band dispersion at the M/L point of the Brillouin zone due to Cu-induced electron doping in ZrSe₂ interlayers. Moreover, electrical measurements in ZrSe₂ revealed semiconducting behavior, while the Cu-intercalated ZrSe₂ exhibited a linear current–voltage curve with metallic character. The atomic intercalation approach may have high potential for realizing transparent electron-doping systems for many specific 2D-based nanoelectronic applications.