Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2004-02-06
Phys. Rev. B 70, 024406 (2004)
Physics
Condensed Matter
Strongly Correlated Electrons
15 pages, 14 figures, submitted to PRB. v2, published version with cosmetic changes
Scientific paper
10.1103/PhysRevB.70.024406
We discuss effects of various impurities on the magnetic susceptibility and the specific heat of the quantum S=1/2 Heisenberg antiferromagnet on a two-dimensional square lattice. For impurities with spin S_i > 0 (here S_i=1/2 in the case of a vacancy or an added spin, and S_i=1 for a spin coupled ferromagnetically to its neighbors), our quantum Monte Carlo simulations confirm a classical-like Curie susceptibility contribution S_i^2/4T, which originates from an alignment of the impurity spin with the local N\'eel order. In addition, we find a logarithmically divergent contribution, which we attribute to fluctuations transverse to the local N\'eel vector. We also study frustrated and nonfrustrated bond impurities with S_i=0. For a simple intuitive picture of the impurity problem, we discuss an effective few-spin model that can distinguish between the different impurities and reproduces the leading-order simulation data over a wide temperature range.
Hoglund Kaj H.
Sandvik Anders. W.
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