Testing the Validity of the Strong Spin-Orbit-Coupling Limit for Octahedrally Coordinated Iridate Compounds in a Model SystemSr3CuIrO6

Abstract

The electronic structure of Sr3CuIrO6, a model system for the 5d Ir ion in an octahedral environment, is studied through a combination of resonant inelastic x-ray scattering (RIXS) and theoretical calculations. RIXS spectra at the Ir L3-edge reveal an Ir t2g manifold that is split into three levels, in contrast to the expectations of the strong spin-orbit-coupling limit. Effective Hamiltonian and ab inito quantum chemistry calculations find a strikingly large non-cubic crystal field splitting comparable to the spin-orbit coupling, which results in a strong mixing of the j eff = 1 2 and j eff = 3 2 states and modifies the isotropic wavefunctions on which many theoretical models are based.

From a Quasimolecular Band Insulator to a Relativistic Mott Insulator in t2g5 Systems with a Honeycomb Lattice Structure

“…However, the crystal structure of Na 2 IrO 3 is known to display the additional trigonal distortion [54], thus significantly departing from the ideal IrO 6 octahedra [21]. This additional distortion can mix the relativistic j eff = 1/2 and 3/2 orbitals, and lead to the splitting of the dominant RIXS peak of the local d-d transition into multiple subpeaks [55,56]. Indeed, we find that the single peak found in Fig.…”

Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed3d−5dTransition-Metal CompoundSr3CuIrO6

“…The physical novelty of this material is demonstrated by the emergence of ferromagnetic order, which is rare in pure cuprates or iridates (the closely related materials Sr 3 CuPtO 6 and Sr 3 ZnIrO 6 are antiferromagnetic) and was used to synthesize random quantum spin chain paramagnetism in Sr 3 CuIr 1−x Pt x O 6 [16,17]. There is to date no microscopic understanding of this unique phenomenon of ferromagnetism.Here, we use Ir L 3 edge resonant inelastic x-ray scattering (RIXS) [5,14,18,19] to reveal a large gap magnetic excitation spectrum in Sr 3 CuIrO 6 and show that it is well described by an effective S = 1/2 ferromagnetic Heisenberg model with an Ising-like exchange anisotropy. We present a microscopic derivation of this model and find that the arrangement of alternating isospins and real spins on the edge-sharing Ir 4+ O 6 -Cu 2+ O 4 chain leads to an unexpected effect, namely, that the ferromagnetic anisotropy arises from the antiferromagnetic superexchange.…”

“…Here, we use Ir L 3 edge resonant inelastic x-ray scattering (RIXS) [5,14,18,19] to reveal a large gap magnetic excitation spectrum in Sr 3 CuIrO 6 and show that it is well described by an effective S = 1/2 ferromagnetic Heisenberg model with an Ising-like exchange anisotropy. We present a microscopic derivation of this model and find that the arrangement of alternating isospins and real spins on the edge-sharing Ir 4+ O 6 -Cu 2+ O 4 chain leads to an unexpected effect, namely, that the ferromagnetic anisotropy arises from the antiferromagnetic superexchange.…”

“…RIXS measurements.-The energy and momentum dependence of the magnetic excitation spectrum in a selfflux-grown Sr 3 CuIrO 6 single crystal was studied by using Ir L 3 edge RIXS, for which dipole transitions excite and deexcite a 2p 3/2 core electron to the 5d orbitals [5,14,18]. The measurements were carried out at beamline 9-ID, Advanced Photon Source, in a horizontal scattering geometry.…”

“…This strong SOC leads to a significant splitting and narrowing of the electronic bands, and pushes 5d TMCs toward the strongly correlated regime. Indeed, the SOC-driven Mott metal-insulator transition was shown to exist in a variety of 5d iridium oxides [2][3][4][5][6][7][8][9][10][11][12][13][14]. An important consequence of this is the entanglement of the orbital and spin degrees of freedom in the resulting localized magnetic moments (termed "isospins"), which can lead to unusual superexchange pathways and to new physics, for example, the proposed spin-liquid state as encoded in the Kitaev model [15] in the honeycomb-lattice (Li,Na) 2 IrO 3 [7] and possible superconductivity in the square-lattice Sr 2 IrO 4 , which shows similar magnetic ordering and dynamics to the cuprates [5].…”