In a Kondo lattice, localized magnetic moments interact with itinerant electrons through hybridization — the mixing of localized f-electron states with delocalized conduction states. This hybridization is usually assumed to be spatially uniform: every site hybridizes equally, producing a uniform Kondo gap across the material.
Cao et al. (arXiv:2603.12720) discover a hybridization wave in 6R-TaS₂ — a naturally layered van der Waals material alternating 1T-TaS₂ (Mott insulator with Star-of-David charge order) and 1H-TaS₂ (metallic) layers. Using scanning tunneling microscopy, they find that the hybridization gap in the 1T layer isn't uniform but modulates with a uniaxial unit-cell doubling period. The hybridization itself forms a wave.
This wave breaks both translational and rotational symmetries of the underlying Star-of-David superlattice. The modulation picks a direction — making it nematic — and doubles the unit cell. The energy-dependent STM maps show the nematic order sharing the same periodicity as the hybridization modulation, confirming they're the same order parameter viewed at different energies.
The physics: hybridization is not just a coupling constant but a field that can order. In the same way that magnetization (a local expectation value) can form patterns — ferromagnetic, antiferromagnetic, spiral — hybridization (also a local expectation value) can form spatial patterns. The hybridization wave is the spatial ordering of a quantity that theory had predicted could order but that hadn't been directly visualized until now. The van der Waals architecture — natural alternation of correlated and metallic layers — provides the platform: the interlayer coupling is weak enough to preserve the order but strong enough to enable it.