Materials Department, University of California, Santa Barbara, CA, 93106, USA.
Department of Physics, Boston College, Chestnut Hill, MA, 02467, USA.
Nat Commun. 2018 Jun 5;9(1):2188. doi: 10.1038/s41467-018-04601-1.
Amplitude modes arising from symmetry breaking in materials are of broad interest in condensed matter physics. These modes reflect an oscillation in the amplitude of a complex order parameter, yet are typically unstable and decay into oscillations of the order parameter's phase. This renders stable amplitude modes rare, and exotic effects in quantum antiferromagnets have historically provided a realm for their detection. Here we report an alternate route to realizing amplitude modes in magnetic materials by demonstrating that an antiferromagnet on a two-dimensional anisotropic triangular lattice (α-NaMnO) exhibits a long-lived, coherent oscillation of its staggered magnetization field. Our results show that geometric frustration of Heisenberg spins with uniaxial single-ion anisotropy can renormalize the interactions of a dense two-dimensional network of moments into largely decoupled, one-dimensional chains that manifest a longitudinally polarized-bound state. This bound state is driven by the Ising-like anisotropy inherent to the Mn ions of this compound.
在凝聚态物理中，源自材料对称破缺的振幅模式引起了广泛的关注。这些模式反映了复杂序参量的振幅振荡，但通常是不稳定的，并衰减为序参量相位的振荡。这使得稳定的振幅模式变得罕见，而量子反铁磁体中的奇异效应一直以来都是它们的检测领域。在这里，我们通过证明二维各向异性三角晶格上的反铁磁体（α-NaMnO）表现出其交错磁化场的长寿命、相干振荡，报告了在磁性材料中实现振幅模式的另一种途径。我们的结果表明，具有单轴各向异性单离子各向异性的海森堡自旋的几何受挫可以重新调整密集二维磁矩网络的相互作用，形成主要去耦的一维链，表现出纵向极化束缚态。这种束缚态是由该化合物中 Mn 离子固有的类 Ising 各向异性驱动的。
