Tuning of the Ru${}^{4+}$ ground-state orbital population in the $4{\mathbf{d}}^4$ Mott insulator Ca${}_2$RuO${}_4$ achieved by La doping

Abstract

The ground-state orbital occupancy of the Ru${}^{4+}$ ion in Ca${}_{2-x}$La${}_x$RuO${}_4$ [x=0, 0.05(1), 0.07(1) and 0.12(1)] was investigated by performing X-ray absorption spectroscopy (XAS) in the vicinity of the O K edge as a function of angle between the incident beam and the surface of the crystals. A minimal model of the hybridization between the O 2p states probed at the K edge and the Ru 4d orbitals was used to analyze the XAS data, allowing the ratio of hole occupancies $n_{xy}/n_{yz,zx}$ to be determined as a function of doping and temperature. For the samples displaying a low-temperature insulating ground-state ($x\le 0.07$), $n_{xy}/n_{yz,zx}$ is found to increase significantly with increasing doping. For x=0.12, which has a metallic ground-state, the XAS spectra are found to be independent of temperature, and not to be describable by the minimal hybridization model. To understand the origin of the evolution of the electronic structure across the phase diagram, we have performed theoretical calculations based on a model Hamiltonian, comprising electron-electron correlations, crystal field ($\Delta$) and spin-orbit coupling ($\lambda$), of a Ru-O-Ru cluster. Our calculations of the Ru hole occupancy as a function of $\Delta /\lambda$ establish that the enhancement of $n_{xy}/n_{yz,zx}$ is driven by significant changes to the crystal field as the tetragonal distortion of the RuO${}_6$ octahedral changes from compressive to tensile with La doping. It also shows that the hole occupancy of the O 2p and Ru 4d orbitals display the same trend as a function of $\Delta /\lambda$, thus validating the minimal hybridization model. In essence, our results suggest that the predominant mechanism driving the emergence of the low-temperature metallic phase in La doped Ca${}_2$RuO${}_4$ is the structurally induced redistribution of holes within the t2g orbitals, rather that the injection of free carriers.

References in corpus (28)

• Angle-resolved photoemission spectroscopy of the cuprate superconductors
• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Strong electronic correlations from Hund's coupling
• Fermi Arcs in a Doped Pseudospin-1/2 Heisenberg Antiferromagnet
• Excitonic Magnetism in Van Vleck-type d^4 Mott Insulators
• Structural and magnetic aspects of the metal insulator transition in Ca${}_{2-x}$Sr${}_x$RuO${}_4$
• Higgs mode and its decay in a two dimensional antiferromagnet
• Collapse of the Mott gap and emergence of a nodal liquid in lightly doped Sr${}_2$IrO${}_4$
• Destruction of the Mott Insulating Ground State of Ca_2RuO_4 by a Structural Transition
• Nature of the Mott transition in Ca2RuO4
• Orbital Dependent Phase Control in Ca2-xSrxRuO4
• Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)
• Hallmarks of Hund's coupling in the Mott insulator Ca${}_2$RuO${}_4$
• In-situ strain-tuning of the metal-insulator-transition of Ca${}_2$RuO${}_4$ in angle-resolved photoemission experiments
• Orbital ordering transition in Ca${}_2$RuO${}_4$ observed with resonant x-ray diffraction
• Subband filling and Mott transition in Ca_{2-x}Sr_xRuO_4
• High pressure diffraction studies on Ca2RuO4
• Resonant X-ray scattering and the $j_{\mathrm{eff}}=1/2$ electronic ground state in iridate perovskites
• Spin-Orbit-Induced Orbital Excitations in Sr2RuO4 and Ca2RuO4: A Resonant Inelastic X-ray Scattering Study
• Orbital occupancies and the putative jeff = 1/2 groundstate in Ba2IrO4: a combined oxygen K edge XAS and RIXS study
• Magnetic Anisotropy and Orbital Ordering in Ca${}_2$RuO${}_4$
• Highly anisotropic magnon dispersion in Ca2RuO4: evidence for strong spin orbit coupling
• Spin-Orbital Excitations in Ca${}_2$RuO${}_4$ Revealed by Resonant Inelastic X-ray Scattering
• Filling Control of the Mott Insulator Ca2RuO4
• Magnon dispersion in Ca2RuO4: impact of spin-orbit coupling and oxygen moments
• Field-induced Orbital Patterns in Ferromagnetic Layered Ruthenates
• Spin-orbit coupling induced Mott transition in Ca${}_{2-x}$Sr${}_x$RuO${}_4$ (0<x<0.2)
• Persistence of antiferromagnetic order upon La substitution in the $4d^4$ Mott insulator Ca${}_2$RuO${}_4$

Cited by in corpus (7)

• Resonant Inelastic X-ray Scattering Study of Ca${}_3$Ru${}_2$O${}_7$
• Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry
• Photoemission Spectrum of Ca2RuO4: Spin Polaron Physics in an S=1 Antiferromagnet with Anisotropies
• Mott-Insulator Ca2RuO4 under a static external electric field
• Orbital-selective metal skin induced by alkali-metal-dosing Mott-insulating Ca${}_2$RuO${}_4$
• Competition of three-dimensional magnetic phases in Ca${}_2$Ru${}_{1-x}$Fe${}_x$O${}_4$: A structural perspective
• Anomalous orbital moment in the ferromagnetic phase of the Sr4Ru3O10