Impurity induced spin texture in quantum critical 2D antiferromagnets
  We describe the uniform and staggered magnetization distributions around a vacancy in a quantum critical two-dimensional S=1/2 antiferromagnet. The distributions are delocalized across the entire sample with a universal functional form arising from an uncompensated Berry phase. The numerical results, obtained using quantum Monte Carlo simulations of the Heisenberg model on bilayer lattices with up to approximately 10^5 spins, are in good agreement with the proposed scaling structure. We determine the exponent eta'=0.40 +/- 0.02, which governs both the staggered and uniform magnetic structure away from the impurity and also controls the impurity spin dynamics. 
Kaj H. Hoglund, Anders W. Sandvik, and Subir Sachdev