Department of Physics and Astronomy, Texas A&M University, College Station, TX, 77843, USA.
Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
Nat Commun. 2019 Mar 8;10(1):1123. doi: 10.1038/s41467-019-08715-y.
The fundamental excitations in an antiferromagnetic chain of spins-1/2 are spinons, de-confined fractional quasiparticles that when combined in pairs, form a triplet excitation continuum. In an Ising-like spin chain the continuum is gapped and the ground state is Néel ordered. Here, we report high resolution neutron scattering experiments, which reveal how a magnetic field closes this gap and drives the spin chains in YbPtPb to a critical, disordered Luttinger-liquid state. In YbPtPb the effective spins-1/2 describe the dynamics of large, Ising-like Yb magnetic moments, ensuring that the measured excitations are exclusively longitudinal, which we find to be well described by time-dependent density matrix renormalization group calculations. The inter-chain coupling leads to the confinement of spinons, a condensed matter analog of quark confinement in quantum chromodynamics. Insensitive to transverse fluctuations, our measurements show how a gapless, dispersive longitudinal mode arises from confinement and evolves with magnetic order.
在一个自旋为 1/2 的反铁磁链中的基本激发是自旋子，它们是解缠的分数准粒子，当它们成对结合时，形成一个三重激发连续体。在类伊辛自旋链中，连续体是带隙的，基态是奈尔有序的。在这里，我们报告了高分辨率的中子散射实验，这些实验揭示了磁场如何关闭这个带隙，并驱动 YbPtPb 中的自旋链进入一个临界的无序的 Luttinger 液体状态。在 YbPtPb 中，有效自旋为 1/2，描述了大的，类伊辛的 Yb 磁矩的动力学，这确保了测量到的激发是纯粹的纵向的，我们发现这可以很好地用时间相关的密度矩阵重整化群计算来描述。链间耦合导致了自旋子的束缚，这是量子色动力学中夸克束缚的凝聚态类比。我们的测量对横向涨落不敏感，它们展示了无带隙的、色散的纵向模式如何从束缚中产生，并随着磁序的演化而演化。
