Complex spin orbital orders in vanadates

The delicate interplay among spin, orbital, charge, lattice degrees of freedom and geometrical frustration can lead to emergent ground states in transition metal oxides, such as complex spin/orbital orders, valence bond solid state, spin/orbital glass, spin/orbital liquids, etc., being of great interest in condensed matter physics. Vanadates have presented rich spin orbital phases. However, many questions are still under debate, for example, the mechanism of spin orders driven by orbital order, orbital fluctuation, metallic V-V bonding, the critical V-V distance that sets the boundary between localized and itinerant electronic behaviors, etc. In the talk, I will present our recent studies on two vanadium systems that both show complex spin/orbital orders, shedding light on roles of localized orbital order and itinerant V-V bonding leading towards a complex spin order.