spindensitywave

Spindensity wave, often referred to as a spin-density wave (SDW), is a type of collective electronic order in metals and quasi-one-dimensional conductors in which the spin density varies periodically in space with a characteristic wave vector Q. The modulation can be accompanied by a weaker or absent charge-density modulation. The spin modulation leads to a magnetic superstructure while the overall crystal lattice remains largely unchanged.

The origin of spindensity waves is typically described in itinerant electron models. When portions of the Fermi surface are well nested by a single wave vector, electron–electron interactions can drive a instability toward a periodic spin polarization with wave vector Q. A mean-field treatment introduces an order parameter for the spin density, mQ, and the formation of the SDW often opens partial gaps on nested regions of the Fermi surface, lowering the electronic energy.

Spindensity waves break translational symmetry and, if the wave vector is incommensurate with the lattice, can break it in a noninteger multiple as well. They usually produce antiferromagnetic-like spin textures with a spatially varying magnetization. The onset of an SDW modifies transport, optical responses, and the Fermi surface topology, and the strength and wave vector of the order can be tuned by doping, pressure, or magnetic field.

Common examples include the SDW order observed in chromium and its alloys; iron-based superconductors where SDW and superconductivity compete or coexist; and various quasi-one-dimensional organic conductors. Detection is typically via neutron scattering, which reveals magnetic Bragg peaks at Q, supported by NMR, muon spin rotation, and spectroscopic probes showing partial gap formation.