Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139.
Center for Quantum Materials, Seoul National University, Seoul 08826, Republic of Korea.
Proc Natl Acad Sci U S A. 2023 Mar 21;120(12):e2208968120. doi: 10.1073/pnas.2208968120. Epub 2023 Mar 14.
Strong interactions between different degrees of freedom lead to exotic phases of matter with complex order parameters and emergent collective excitations. Conventional techniques, such as scattering and transport, probe the amplitudes of these excitations, but they are typically insensitive to phase. Therefore, novel methods with phase sensitivity are required to understand ground states with phase modulations and interactions that couple to the phase of collective modes. Here, by performing phase-resolved coherent phonon spectroscopy (CPS), we reveal a hidden spin-lattice coupling in a vdW antiferromagnet FePS that eluded other phase-insensitive conventional probes, such as Raman and X-ray scattering. With comparative analysis and analytical calculations, we directly show that the magnetic order in FePS selectively couples to the trigonal distortions through partially filled t orbitals. This magnetoelastic coupling is linear in magnetic order and lattice parameters, rendering these distortions inaccessible to inelastic scattering techniques. Our results not only capture the elusive spin-lattice coupling in FePS but also establish phase-resolved CPS as a tool to investigate hidden interactions.
强相互作用导致不同自由度之间的物质具有复杂的序参量和涌现的集体激发。传统的技术，如散射和输运，探测这些激发的幅度，但它们通常对相位不敏感。因此，需要具有相位灵敏度的新方法来理解具有相位调制和与集体模式相位耦合的相互作用的基态。在这里，通过执行相分辨相干声子谱（CPS），我们揭示了 vdW 反铁磁体 FePS 中隐藏的自旋-晶格耦合，这使得其他相位不敏感的常规探针（如拉曼和 X 射线散射）无法探测到。通过比较分析和解析计算，我们直接表明 FePS 中的磁有序通过部分填充的 t 轨道选择性地与三角畸变耦合。这种磁弹耦合与磁有序和晶格参数呈线性关系，使得这些畸变无法通过非弹性散射技术来探测。我们的结果不仅捕捉到了 FePS 中难以捉摸的自旋-晶格耦合，还确立了相分辨 CPS 作为一种研究隐藏相互作用的工具。
