Ergeçen Emre, Ilyas Batyr, Mao Dan, Po Hoi Chun, Yilmaz Mehmet Burak, Kim Junghyun, Park Je-Geun, Senthil T, Gedik Nuh
Department of Physics, Massachusetts Institute of Technology, Cambridge, 02139, MA, USA.
Department of Physics, Hong Kong Univesity of Science and Technology, Clear Water Bay, Hong Kong, 999077, China.
Nat Commun. 2022 Jan 10;13(1):98. doi: 10.1038/s41467-021-27741-3.
In van der Waals (vdW) materials, strong coupling between different degrees of freedom can hybridize elementary excitations into bound states with mixed character. Correctly identifying the nature and composition of these bound states is key to understanding their ground state properties and excitation spectra. Here, we use ultrafast spectroscopy to reveal bound states of d-orbitals and phonons in 2D vdW antiferromagnet NiPS. These bound states manifest themselves through equally spaced phonon replicas in frequency domain. These states are optically dark above the Néel temperature and become accessible with magnetic order. By launching this phonon and spectrally tracking its amplitude, we establish the electronic origin of bound states as localized d-d excitations. Our data directly yield electron-phonon coupling strength which exceeds the highest known value in 2D systems. These results demonstrate NiPS as a platform to study strong interactions between spins, orbitals and lattice, and open pathways to coherent control of 2D magnets.
在范德华（vdW）材料中，不同自由度之间的强耦合可以将基本激发杂化成为具有混合特性的束缚态。正确识别这些束缚态的性质和组成是理解其基态性质和激发光谱的关键。在这里，我们使用超快光谱来揭示二维范德华反铁磁体NiPS中d轨道和声子的束缚态。这些束缚态通过频域中均匀间隔的声子复制态表现出来。这些态在尼尔温度以上是光学暗态，随着磁序的出现而变得可探测。通过激发这种声子并在光谱上跟踪其振幅，我们确定了束缚态的电子起源是局域化的d-d激发。我们的数据直接得出了电子-声子耦合强度，该强度超过了二维系统中已知的最高值。这些结果表明NiPS是研究自旋、轨道和晶格之间强相互作用的一个平台，并为二维磁体的相干控制开辟了途径。
