QUANTUM CORRECTIONS TO THE SPIN-CORRELATION FUNCTION AND THE SPIN-STIFFNESS CONSTANT IN A 2-DIMENSIONAL HEISENBERG-ANTIFERROMAGNET AT ZERO TEMPERATURE

Quantum corrections to the longitudinal spin-correlation function and the spin-stiffness constant are calculated up to 1/(2S)2 in a two-dimensional Heisenberg antiferromagnet at zero temperature by using the Holstein-Primakoff transformation. The equal-time longitudinal spin-correlation function is found to compensate almost entirely the reduction caused by the second-order correction in the transverse spin-correlation function, making the spherically averaged correlation function very close to the value given by linear spin-wave theory. In the spin-stiffness constant, a partial cancellation is found between the "paramagnetic" and "diamagnetic" terms, leading to a small second-order correction.