Spin-flop transitions and spin-wave gaps in La_2CuO_4

TL;DR

This paper investigates the spin-wave spectrum and spin-flop transitions in La_2CuO_4 under magnetic fields, revealing a two-step magnetization rotation and confirming theoretical predictions with experimental data.

Contribution

The study introduces a detailed theoretical analysis of spin-flop transitions in La_2CuO_4 using the non-linear sigma-model, matching experimental observations.

Findings

Two-step rotation of the staggered magnetization under certain field directions

Conventional spin-flop transition for perpendicular magnetic fields

Excellent agreement between theoretical predictions and experimental measurements

Abstract

We study the spin-wave spectrum and the spin-flop transitions in La_2CuO_4 in a uniform magnetic field at zero temperature. Using the non-linear sigma-model, we show that a field applied along the orthorhombic b direction leads to a two-step rotation of the staggered magnetization, first in the bc and then in the ac plane, until the order parameter is completely aligned along the c axis. In contrast, for a perpendicular magnetic field, we find a conventional spin-flop transition induced by the competition between the field and the interlayer coupling. A comparison with recent measurements of the field-dependence of the in-plane spin-wave gap shows a beautiful agreement between theory and experiments.