Time-reversal symmetry breaking superconducting ground state in the   doped Mott insulator on the honeycomb lattice
  The emergence of superconductivity in doped Mott insulators has been debated for decades. In this paper, we report the theoretical discovery of a time-reversal symmetry breaking superconducting ground state in the doped Mott insulator (described by the well known t-J model) on honeycomb lattice, based on a recently developed variational method: the Grassmann tensor product state approach. As a benchmark, we use exact diagonalization and density-matrix renormalization methods to check our results on small clusters. We find systematic consistency for the ground-state energy as well as other physical quantities, such as the staggered magnetization. At low doping, the superconductivity coexists with antiferromagnetic ordering. 
Zheng-Cheng Gu, Hong-Chen Jiang, D. N. Sheng, Hong Yao, Leon Balents,   and Xiao-Gang Wen
cond-mat.str-el cond-mat.mtrl-sci cond-mat.supr-con quant-ph