Magnetic correlations and quantum criticality in the insulating antiferromagnetic , insulating spin liquid , renormalized Fermi liquid , and metallic antiferromagnetic phases of the Mott system

Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal neutron scattering. Specifically we have studied the antiferromagnetic and paramagnetic phases of metallic V2−yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a Heisenberg localized spin model, the long range order in the antiferromagnetic metal is an incommensurate spin-densitywave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a “single lobe” spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for h̄ω < kBT in the paramagnetic insulator carry substantial magnetic spectral weight. However, the correlation length is extremely short, extending only to the nearest neighbor distance. The phase transition to the antiferromagnetic insulator, from the paramagnetic metal and the paramag-