Quantum spin fluctuations for a distorted incommensurate spiral

Quantum spin fluctuations are investigated for the distorted incommensurate spiral state of a geometrically frustrated triangular-lattice antiferromagnet. With increasing easy axis anisotropy, the average reduction of the spin amplitude by quantum fluctuations is suppressed but the spiral also becomes more distorted. Quantum fluctuations enhance both the wave vector of the distorted spiral and the critical anisotropy above which it undergoes a first-order transition into a collinear state. An experimental technique is proposed to isolate the effects of quantum fluctuations from the classical distortion of the spiral. This analysis is applied to the elliptical spiral state of doped CuFeO ₂.