Laurita N J, Luo Yi, Hu Rongwei, Wu Meixia, Cheong S W, Tchernyshyov O, Armitage N P
The Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
Rutgers Center For Emergent Materials, Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
Phys Rev Lett. 2017 Dec 1;119(22):227601. doi: 10.1103/PhysRevLett.119.227601.
The symmetric splitting of two spin-wave branches in an antiferromagnetic resonance (AFR) experiment has been an essential measurement of antiferromagnets for over half a century. In this work, circularly polarized time-domain THz spectroscopy experiments performed on the low symmetry multiferroic hexagonal HoMnO_{3} reveal an AFR of the Mn sublattice to split asymmetrically in an applied magnetic field, with an ≈50% difference in g factors between the high and low energy branches of this excitation. The temperature dependence of the g factors, including a drastic renormalization at the Ho spin ordering temperature, reveals this asymmetry to unambiguously stem from Ho-Mn interactions. Theoretical calculations demonstrate that the AFR asymmetry is not explained by conventional Ho-Mn exchange mechanisms alone and is only reproduced if quartic spin interactions are also included in the spin Hamiltonian. Our results provide a paradigm for the optical study of such novel interactions in hexagonal manganites and low symmetry antiferromagnets in general.
在反铁磁共振（AFR）实验中，两个自旋波分支的对称分裂半个多世纪以来一直是反铁磁体的一项重要测量手段。在这项工作中，对低对称性多铁性六角形HoMnO₃进行的圆偏振时域太赫兹光谱实验表明，在施加磁场时，Mn亚晶格的AFR会不对称分裂，这种激发的高能和低能分支之间的g因子相差约50%。g因子的温度依赖性，包括在Ho自旋有序温度下的剧烈重整化，表明这种不对称性明确源于Ho-Mn相互作用。理论计算表明，AFR不对称性不能仅由传统的Ho-Mn交换机制来解释，只有在自旋哈密顿量中也包含四次自旋相互作用时才能重现。我们的结果为一般情况下六角锰酸盐和低对称性反铁磁体中此类新型相互作用的光学研究提供了一个范例。
