Persistent Paramagnons Deep in the Metallic Phase of ${\mathrm{Sr}}_{2-x}{\mathrm{La}}_x{\mathrm{IrO}}_4$

Journal Article · Thu Sep 01 00:00:00 EDT 2016 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.117.107001· OSTI ID:1341420

Gretarsson, H.; Sung, N. H.; Porras, J.; Bertinshaw, J.; Dietl, C.; Bruin, Jan A. N.; Bangura, A. F.; Kim, Y. K.; Dinnebier, R.; Kim, Jungho; Al-Zein, A.; Moretti Sala, M.; Krisch, M.; Le Tacon, M.; Keimer, B.; Kim, B. J.

We have studied the magnetic excitations of electron-doped Sr_2-xLa_xIrO₄ (0 ≤ x ≤ 0.10) using resonant inelastic x-ray scattering at the Ir L₃ edge. The long-range magnetic order is rapidly lost with increasing x, but two-dimensional short-range order (SRO) and dispersive magnon excitations with nearly undiminished spectral weight persist well into the metallic part of the phase diagram. The magnons in the SRO phase are heavily damped and exhibit anisotropic softening. Their dispersions are well described by a pseudospin-1=2 Heisenberg model with exchange interactions whose spatial range increases with doping. We also find a doping-independent high-energy magnetic continuum, which is not described by this model. The spin-orbit excitons arising from the pseudospin-3=2 manifold of the Ir ions broaden substantially in the SRO phase, but remain largely separated from the low-energy magnons. Pseudospin-1=2 models are therefore a good starting point for the theoretical description of the low-energy magnetic dynamics of doped iridates.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: Alexander von Humboldt Foundation; German Research Foundation (DFG)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1341420
• Journal Information: Physical Review Letters, Vol. 117, Issue 10; ISSN 0031-9007
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS