paper

Theory of Two-Dimensional Quantum Heisenberg Antiferromagnets with a Nearly Critical Ground State

arXiv:cond-mat/9304046 · doi:10.1103/PhysRevB.49.11919

Abstract

We present the general theory of clean, two-dimensional, quantum Heisenberg antiferromagnets which are close to the zero-temperature quantum transition between ground states with and without long-range Néel order. For Néel-ordered states, `nearly-critical' means that the ground state spin-stiffness, , satisfies , where is the nearest-neighbor exchange constant, while `nearly-critical' quantum-disordered ground states have a energy-gap, , towards excitations with spin-1, which satisfies . Under these circumstances, we show that the wavevector/frequency-dependent uniform and staggered spin susceptibilities, and the specific heat, are completely universal functions of just three thermodynamic parameters. Explicit results for the universal scaling functions are obtained by a expansion on the quantum non-linear sigma model, and by Monte Carlo simulations. These calculations lead to a variety of testable predictions for neutron scattering, NMR, and magnetization measurements. Our results are in good agreement with a number of numerical simulations and experiments on undoped and lightly-doped .

81 pages, REVTEX 3.0, smaller updated version, YCTP-xxxx

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