1206.5381 (Jia-Wei Mei et al.)

Spin Structures of Spin-Orbit Coupled Square-Lattice Antiferromagnets    [PDF]

Jia-Wei Mei, A. Zheludev

Ba$_2$CuGe$_2$O$_7$ is a model material for both experimental and theoretical investigations of quasi-2D spin-orbit coupled square-lattice antiferromagnets (AFM). At low temperatures in magnetic fields along z-axis, Ba$_2$CuGe$_2$O$_7$ have three different spin structures in the experiments: the incommensurate (IC) spiral state, the double-$k$ state and antiferromagnetic (AF) N\'eel state. The double-$k$ state is an intermediate phase separating the IC state and AF N\'eel state by two first-order transitions. It has the Bragg vectors at both IC and AF propagation vectors. The three phases are verified in the theoretical study on the spin-orbit coupled square-lattice AF $S=1/2$ spin model. The spin-chirality can be used to classify different phases. In contradiction to spin-orbit coupled ferromagnets, the skyrmion lattice is not the ground state of Ba$_2$CuGe$_2$O$_7$. In the spiral phase, the phason mode along the IC propagating direction is a realization of the one-gap integrable Lam\'e problem.

View original: http://arxiv.org/abs/1206.5381