Doping the chiral spin liquid: Topological superconductor or chiral metal

Abstract

We point out that there are two different chiral spin liquid states on the triangular lattice and discuss the conducting states that are expected on doping them. These states labeled CSL1 and CSL2 are associated with two distinct topological orders with different edge states, although they both spontaneously break time reversal symmetry and exhibit the same quantized spin Hall conductance. While CSL1 is related to the Kalmeyer-Laughlin state, CSL2 is the ν=4 member of Kitaev's 16-fold way classification. Both states are described within the Abrikosov fermion representation of spins, and the effect of doping can be accessed by introducing charged holons. On doping CSL2, condensation of charged holons leads to a topological d + id superconductor. However on doping CSL1, in sharp contrast, two different scenarios can arise: first, if holons condense, a chiral metal with enlarged unit cell and finite Hall conductivity is obtained. However, in a second novel scenario, the internal magnetic flux adjusts with doping and holons form a bosonic integer quantum Hall state. Remarkably, the latter phase is identical to a d+id superconductor. In this case the Mott insulator to superconductor transition is associated with a bosonic variant of the integer quantum Hall plateau transition. We connect the above two scenarios to two recent numerical studies of doped chiral spin liquids on a triangular lattice. Our work clarifies the complex relation between topological superconductors, chiral spin liquids, and quantum criticality.

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