Resonating valence bond states in 2 and 3D - brief history and recent examples

Abstract

Resonating valence bond states are quantum spin liquids, having low energy spin- ½ (spinon) or spin-1 excitations. Although spins are 'disordered', they possess subtle topological orders and some times chiral orders. RVB states are easily appreciated and seem natural in the quantum fluctuation dominated 1D world. In 2 and 3D, competing orders such as antiferromagnetism, charge order or even superconductivity often hide an underlying robust quantum spin liquid state. Introduction of additional spin interactions or doping of delocalized charges, or finite temperatures, could frustrate the long range magnetic order and reveal a robust RVB state. To this extent they are natural in 2D and above. We present a brief history of insulating RVB states. Then we summarise our own recent theory of RVB states for 2 and 3D systems, including some newly synthesised ones: (i) boron doped diamond, (ii) Na_xCoO₂:yH₂O , (iii) quasi 2D organic conductors and (iv) a 2D graphene sheet.