Spin Nematic Order — Quadrupolar Hidden Order
Spin-1 System · Q_αβ Tensor · Field-Induced Transitions · NMR Invisible Order
Parameters
Temperature T/J:
0.5
Magnetic field h:
0.0
Biquadratic K/J:
0.5
Director angle θ:
45°
Nematic Directors
Phase Diagram
Order Parameter
▶ Animate
Spin nematic:
Spin-1 system with ⟨S⟩=0 but ⟨S_α S_β⟩≠0 — quadrupolar order. "Hidden order" invisible to neutron scattering (no magnetic Bragg peaks).
Order parameter:
Q_αβ = ⟨S_αS_β + S_βS_α⟩/2 − (2/3)δ_αβ (traceless tensor, rank-2).
Examples:
NiGa₂S₄, iron-based superconductors "hidden order" compound URu₂Si₂ may be spin nematic.