Anisotropic softening of magnetic excitations in lightly electron-dopedSr2IrO4

Abstract

The magnetic excitations in electron doped (Sr1−xLax)2IrO4 with x = 0.03 were measured using resonant inelastic X-ray scattering at the Ir L3-edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the anti-nodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron doped (Sr1−xLax)2IrO4 with close analogies to the hole doped cuprates, further motivating the search for high temperature superconductivity in this system. PACS numbers: 71.27.+a, 74.25.Ha, 78.70.Dm Together with the tremendous research activity on the superconducting cuprates [1,2], efforts to compare the cuprates with other related systems have also been on-going for decades. Such comparison serves as a natural approach to clarify the roles of multiple emergent phenomena in the phase diagram of the cuprates, including magnetic fluctuations, superconductivity, pseudo gap and charge density waves etc. The 5d oxide Sr 2 IrO 4 is an excellent candidate for such study. This so called spin-orbit-coupling driven Mott insulator [3] is in close proximity to the single layered cuprate La 2 CuO 4 , both structure-wise [4] and electronically [5][6][7][8]. Sr 2 IrO 4 hosts a single hole in the t 2g manifold where a Mott gap is opened, assisted by strong spin-orbit coupling [3,9,10], and its magnetic excitation spectrum can be well described using a Heisenberg model of effective spin-1 2 moments on a square lattice [11,12]. With a minimum single band model, Sr 2 IrO 4 and La 2 CuO 4 are strikingly similar [13], leading to the proposal that this compound could also host unconventional high temperature superconductivity (HTS) upon doping [13,14]. Moreover, due to the opposite signs of the nextnearest-neighbor hopping integral in these two systems, theoretical work further suggests that the electron doped Sr 2 IrO 4 might be more closely analogous to those of hole (rather than electron) doped cuprates [13,14].Although the phase diagram of doped Sr 2 IrO 4 has not been fully explored, a large amount of experimental work supports the hypothesis that the Fermiology of the doped iridates is closely analogous to the cuprates. Upon doping with La up to 6%, Sr 2 IrO 4 evolves from an antiferromagnetically ordered insulator to a paramagnetic [15] or percolative [16] metal. A T-linear resistivity was observed with potassium substitution [15]. Further, angle-resolved photoemission spectroscopy (ARPES) data from several groups [5][6][7]17] has shown convincingly that doping indeed drives a similar low energy electron evolution as observed in the cuprates. An anisotropic pseudo gap opens on the Fermi surface, with the same symmetry as that of the cuprates. However, the related question of whether the magnetic correlations that ...

Strong anisotropy within a Heisenberg model in the Jeff=12 insulating state of Sr2Ir0.8Calder1, Kim2, Taylor3 et al. 2016Phys. Rev. BSelf Cite7040View 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.…”

Giant spin gap and magnon localization in the disordered Heisenberg antiferromagnet Sr2Ir1−xRuxO4Cao1, Liu2, Xu3 et al. 2017Phys. Rev. BSelf Cite10190View full textAdd to dashboardCite

“…Specifically, the magnetic excitation energies at (π, 0) are robust against doped charge carriers and in this work disorder, while profound changes take place around e.g. (π, π) and (π/2, π/2) 7,8,24,25,33 . This similarity is not necessarily expected as it involves comparing the effects of itinerant carriers introduced by out-of-plane atomic substitutions with in-plane replacement of the Ir atoms.…”

“…The results here reflect the strong local correlation in the material that voids mean-field descriptions. Such a result is reminiscent of studies of electron and hole doped cuprates and iridates [6][7][8][9]24,25,[30][31][32] , albeit up to smaller maximum doping level of 40% in cuprates and a mere 10% in iridates. Specifically, the magnetic excitation energies at (π, 0) are robust against doped charge carriers and in this work disorder, while profound changes take place around e.g.…”

“…Furthermore, single crystals of Sr 2 Ir 1−x M x O 4 can be produced where Ir is substituted with a different transition metal M over a wide range [16][17][18][19][20] . This, combined with recent progress in applying resonant inelastic X-ray scattering (RIXS) 9,21 to iridates [22][23][24][25][26] provides an excellent opportunity to determine the magnetic interactions and correlations in disordered (pseudo)spin-1/2 Heisenberg antiferromagnets.…”

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

“…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.…”