Persistent Paramagnons Deep in the Metallic Phase ofSr2−xLaxIrO4

Abstract

We have studied the magnetic excitations of electron-doped Sr_{2-x}La_{x}IrO_{4} (0≤x≤0.10) using resonant inelastic x-ray scattering at the Ir L_{3} 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.

Dispersive magnetic and electronic excitations in iridate perovskites probed by oxygen K -edge resonant inelastic x-ray scattering

“…1(c)] as observed in previous Ir L 3 RIXS experiments [16,48]. C can be easily attributed to a spin-orbit exciton mode (at ∼0.7 eV) [17,18,49] that exhibits a minor dispersion and strong intensity [16,48]. The mode B finds direct correspondence with the excitonic quasiparticle (spin-orbit exciton "dressed" by magnons) reported in Ref.…”

Persistence of antiferromagnetic order upon La substitution in the 4d4 Mott insulator Ca2RuO4

“…The only effects of La doping on the magnetic structure are to suppress the A-centred mode, favoring the B mode instead, and to reduce the Néel temperature somewhat. Our results are discussed with reference to previous experimental reports on the effects of cation substitution on the d 4 Mott insulator Ca 2 RuO 4 , as well as with regard to theoretical studies on the evolution of its electronic and magnetic structure. In particular, our results rule out the presence of a proposed ferromagnetic phase, and suggest that the structural effects associated with La substitution play an important role in the physics of the system.…”

“…In perovskite manganites, the parent antiferromagnetic (AFM) order develops into a ferromagnetic (FM) phase hosting giant magnetoresistance [2]. On the other hand, in both S = 1/2 cuprates [1] and J eff = 1/2 iridates [3][4][5][6], doping suppresses long-range AFM order leading to the formation of incommensurate spin-density wave order [7][8][9][10] with a conventional paramagnetic (PM) metal eventually emerging.…”

Strong anisotropy within a Heisenberg model in the Jeff=12 insulating state of Sr2Ir0.8Calder1, Kim2, Taylor3 et al. 2016Phys. Rev. B7040View full textAdd to dashboardCite

“…3 The final point is the most striking and a departure from RIXS measurements of doping on the Sr site that shows no spin gap in the RIXS spectra 12,13 and is consistent with recent measurements on higher Ru doping 20 . As noted there is some debate in the literature for the undoped case with several studies showing no spin-gap, Refs.…”