Perturbing the kagome lattice spin-liquid state: Raman scattering, magnetic field, and doping.

Wing-Ho Ko, MIT.

Abstract: Spin 1/2 kagome system, realized recently in herbertsmithite ZnCu3(OH)6Cl2, holds the great promise of realizing the U(1) Dirac spin-liquid (DSL) state—an exotic state of matter that is strongly interacting and yet breaks no spin or lattice symmetries.

In this talk I'll discuss my theoretical work on the effect of Raman scattering, magnetic field, and hole doping on the DSL state. For Raman scattering, I'll show that spinons give rise to a broad continuum in the Raman spectrum, and an emergent gauge field give rise to a collective excitation that shows up in a 1/ω singularity. For external magnetic field, I'll show that the resulting state contains a Goldstone boson, which signifies a broken XY-order in the ground state. In the doped case, an analogous Goldstone boson is also found, but is eaten up by the electromagnetic field to produce a superconductor, which turns out to have hc/4e vortices and quasiparticles with semionic mutual statistics.

Reference: W.-H. Ko, Z.-X. Liu, T.-K. Ng, and P. A. Lee, arXiv:0910.5468
W.-H. Ko, P. A. Lee, and X.-G. Wen, Phys. Rev. B 79, 214502 (2009)
Y. Ran, W.-H. Ko, P. A. Lee, and X.-G. Wen, Phys. Rev. Lett. 102, 047205 (2009)