ESPCI web site
Thursday October 17 at 2:00 pm (Paris time)
Quantum Spin Nematic Phase in a Square-lattice Iridate
Spin nematic (SN) is a magnetic analog of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid [1, 2]. Particularly intriguing is a valence-bond SN, in which spins are quantum entangled to form a multi-polar order without breaking time-reversal symmetry, but its unambiguous experimental realization remains elusive. In this talk, I will discuss on our recent discovery of a SN phase in the square-lattice iridate Sr2IrO4, which approximately realizes a pseudospin one-half Heisenberg antiferromagnet (AF) in the strong spin-orbit coupling limit [3]. Upon cooling, the transition into the SN 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 (AF) phase below TN 230 K, and becomes directly observable through its interference with the AF order in resonant x-ray diffraction, which allows us to 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 resonating-valence-bond-like quantum entanglement in the AF state. Taken together, our results reveal a quantum order underlying the Neel AF that is widely believed to be intimately connected to the mechanism of high temperature superconductivity [4].
Figure1 : A schematic of the Neel AF and SN orders overlaid on the crystal structure of Sr2IrO4.
1. M. Blume and Y. Y. Hsieh, J. Appl. Phys. 40, 1249–1249349 (1969).
2. A. F. Andreev and I. A. Grishchuk, Sov. Phys. JETP 60, 267 (1984).
3. J. Bertinshaw, Y. K. Kim, G. Khaliullin, and B. J. Kim, Annu. Rev. Condens. Matter Phys. 10, 315–336 (2019).
4. H. Kim et al., Nature (in press).
