In-plane anisotropy of charge density wave fluctuations in 1T-TiSe₂

The layered transition-metal dichalcogenide 1T-TiSe₂ is a rich platform for charge-density-wave (CDW) physics, encompassing excitonic condensation, emergent superconductivity, and the debated chiral CDW. Using X-ray diffuse scattering, we reveal anisotropic triple-q CDW fluctuations over a large region of reciprocal space. Above the CDW transition temperature, the in-plane diffuse signal appears as ellipses, while the out-of-plane signal forms rodlike features. The orientation of the in-plane ellipses indicates chainlike correlations of Ti and Se atoms transverse to the CDW wave vector, and the rods signify a loss of interlayer phase coherence. Our analysis further shows that the three CDW components host independent phase fluctuations with π phase slips across domain walls. The resulting hierarchy of length scales points to intricate fluctuation patterns that go beyond the conventional 2D-3D crossover picture.