Unveiling New Charge Ordering in 2H-NbSe₂

Layered transition metal dichalcogenides (TMDs), such as 2H-ASe₂ (A = Ta, V, Nb), exhibit fascinating coexistence of exotic superconductivity and charge density waves (CDW) states in bulk crystals. The electronic correlations and strong electron-phonon coupling (EPC) are predicted to play a role in the formation of CDWs in NbSe₂. However, it remains unclear which interaction is primarily responsible for driving the phase transition. In this study, we investigated the atomic-scale behavior of CDWs in NbSe₂ under local strain using scanning tunneling microscopy (STM). Strain influences electron-electron interactions and EPC, which can lead to the emergence of new electronic phases. A novel tri-directional (3Q) CDW order, with a periodicity of 2√𝟑 a₀ X 2 √𝟑 a₀ R(30^o), was observed in bulk NbSe₂. This finding indicates that spatial variations in strain lead to the coexistence of a unidirectional (1Q) 4a₀ X 1a₀ stripe CDW order alongside the newly discovered 3Q CDW order. This coexistence suggests a critical point in the quantum phase transition and indicates momentum and orbital dependence of the electron-phonon coupling. Our results provide a framework for studying strain-induced CDW modulation and phase transition in TMDs.