Quantum spin nematic phase in a squarelattice iridate

Spin nematic is a magnetic analogue of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid1,2. Particularly intriguing is a valence-bond spin nematic3-5, in which spins are quantum entangled to form a multipolar order without breaking time-reversal...

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Published in:Nature (London) 2024-01, Vol.625 (7994), p.264-269F
Main Authors: Kim, Hoon, Kim, Jin-Kwang, Kwon, Junyoung, Kim, Jimin, Kim, Hyun-Woo J, Ha, Seunghyeok, Kim, Kwangrae, Lee, Wonjun, Kim, Jonghwan, Cho, Gil Young, Heo, Hyeokjun, Jang, Joonho, Sahle, C J, Longo, A, Strempfer, J, Fabbris, G, Choi, Y, Haskel, D, Kim, Jungho, Kim, J-W, Kim, B J
Format: Article
Language:English
Subjects:
Antiferromagnetism
Coherent scattering
Crystals
Electrons
High temperature
Inelastic scattering
Liquid crystals
Magnons
Quadrupoles
Quantum entanglement
Raman spectra
Raman spectroscopy
Spin-orbit interactions
Symmetry
Temperature
X-ray diffraction
X-ray scattering
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Summary:Spin nematic is a magnetic analogue of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid1,2. Particularly intriguing is a valence-bond spin nematic3-5, in which spins are quantum entangled to form a multipolar order without breaking time-reversal symmetry, but its unambiguous experimental realization remains elusive. Here we establish a spin nematic phase in the square-lattice iridate Sr2IrO4, which approximately realizes a pseudospin one-half Heisenberg antiferromagnet in the strong spin-orbit coupling limit6-9. Upon cooling, the transition into the spin nematic phase at Tc ≈ 263 K is marked by a divergence in the static spin quadrupole susceptibility extracted from our Raman spectra and concomitant emergence of a collective mode associated with the spontaneous breaking of rotational symmetries. The quadrupolar order persists in the antiferromagnetic phase below TN ≈ 230 K and becomes directly observable through its interference with the antiferromagnetic order in resonant X-ray diffraction, which allows usto uniquely determine its spatial structure. Further, we find using resonant inelastic X-ray scattering a complete breakdown of coherent magnon excitations at short-wavelength scales, suggesting a many-body quantum entanglement in the antiferromagnetic state10,11. Taken together, our results reveal a quantum order underlying the Néel antiferromagnet that is widely believed to be intimately connected to the mechanism of high-temperature superconductivity12,13.
ISSN:0028-0836
1476-4687
DOI:10.1038/s41586-023-06829-4