THEORY OF 2-DIMENSIONAL QUANTUM HEISENBERG ANTIFERROMAGNETS WITH A NEARLY CRITICAL GROUND-STATE

Review

关键词: SUPERCONDUCTOR-INSULATOR TRANSITION;    NUCLEAR MAGNETIC-RELAXATION;    RESONATING-VALENCE-BOND;    NONLINEAR SIGMA-MODELS;    LARGE-N EXPANSION;    EXACT MASS GAP;    FINITE-SIZE;    SPIN CORRELATIONS;    LOW-TEMPERATURES;    DOPED ANTIFERROMAGNET;   

DOI  :  10.1103/PhysRevB.49.11919

来源: SCIE

【 摘 要 】

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 Neel order. While some of our discussion is more general, the bulk of our theory will be restricted to antiferromagnets in which the Neel order is described by a three-vector order parameter. For Neel-ordered states, ''nearly critical'' means that the ground-state spin stiffness, rho(s), satisfies rho(s) much less than J, where J is the nearest-neighbor exchange constant, while ''nearly-critical'' quantum-disordered ground states have an energy gap, DELTA, towards excitations with spin 1, which satisfies DELTA much less than J. The allowed temperatures, T, are also smaller than J, but no restrictions are placed on the values of k(B)T/rho(s) or k(B)T/DELTA. Under these circumstances, we show that the wave vector and/or frequency-dependent uniform and staggered spin susceptibilities, and the specific heat, are completely universal functions of just three thermodynamic parameters. On the ordered side, these three parameters are rho(s), the T = 0 spin-wave velocity c, and the ground-state staggered moment No; previous works have noted the universal dependence of the susceptibilities on these three parameters only in the more restricted regime of k(B)T much less than rho(s). On the disordered side the three thermodynamic parameters are DELTA, c, and the spin-1 quasiparticle residue A. Explicit results for the universal scaling functions are obtained by a 1/N expansion on the O(N) quantum nonlinear 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 La2-deltaSrdeltaCuO4.

【 授权许可】

Free