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Coherent many-body exciton in van der Waals antiferromagnet NiPS3

DOI: 10.1038/s41586-020-2520-5 DOI Help

Authors: Soonmin Kang (Institute for Basic Science; Seoul National University) , Kangwon Kim (Sogang University) , Beom Hyun Kim (Korea Institute for Advanced Study) , Jonghyeon Kim (Yonsei University) , Kyung Ik Sim (Yonsei University) , Jae-ung Lee (Sogang University; Ajou University) , Sungmin Lee (Institute for Basic Science; Seoul National University) , Kisoo Park (Institute for Basic Science; Seoul National University) , Seokhwan Yun (Institute for Basic Science; Seoul National University) , Taehun Kim (Institute for Basic Science; Seoul National University) , Abhishek Nag (Diamond Light Source) , Andrew Walters (Diamond Light Source) , Mirian Garcia-fernandez (Diamond Light Source) , Jiemin Li (Diamond Light Source) , Laurent Chapon (Diamond Light Source) , Kejin Zhou (Diamond Light Source; Swiss Light Source) , Young-woo Son (Korea Institute for Advanced Study) , Jae Hoon Kim (Yonsei University) , Hyeonsik Cheong (Sogang University) , Je-geun Park (Institute for Basic Science; Seoul National University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature , VOL 37

State: Published (Approved)
Published: July 2020
Diamond Proposal Number(s): 18503 , 18906

Abstract: An exciton is the bosonic quasiparticle of electron–hole pairs bound by the Coulomb interaction. Bose–Einstein condensation of this exciton state has long been the subject of speculation in various model systems and examples have been found more recently in optical lattices and two-dimensional materials. Unlike these conventional excitons formed from extended Bloch states, excitonic bound states from intrinsically many-body localized states are rare. Here we show that a spin–orbit-entangled exciton state appears below the Néel temperature of 150 kelvin in NiPS3, an antiferromagnetic van der Waals material. It arises intrinsically from the archetypal many-body states of the Zhang–Rice singlet, and reaches a coherent state assisted by the antiferromagnetic order. Using configuration-interaction theory, we determine the origin of the coherent excitonic excitation to be a transition from a Zhang–Rice triplet to a Zhang–Rice singlet. We combine three spectroscopic tools—resonant inelastic X-ray scattering, photoluminescence and optical absorption—to characterize the exciton and to demonstrate an extremely narrow excitonic linewidth below 50 kelvin. The discovery of the spin–orbit-entangled exciton in antiferromagnetic NiPS3 introduces van der Waals magnets as a platform to study coherent many-body excitons.

Subject Areas: Physics, Materials

Instruments: I21-Resonant Inelastic X-ray Scattering (RIXS)