Van Vleck excitons in Ca${}_2$RuO${}_4$

Abstract

A framework is presented for modeling and understanding magnetic excitations in localized, intermediate coupling magnets where the interplay between spin-orbit coupling, magnetic exchange, and crystal field effects are known to create a complex landscape of unconventional magnetic behaviors and ground states. A spin-orbit exciton approach for modeling these excitations is developed based upon a Hamiltonian which explicitly incorporates single-ion crystalline electric field and spin exchange terms. This framework is then leveraged to understand a canonical Van Vleck $j{}_{\mathrm{eff}}=0$ singlet ground state whose excitations are coupled spin and crystalline electric field levels. Specifically, the anomalous Higgs mode [Jain et al. Nat. Phys. 13, 633 (2017)], spin-waves [S. Kunkemöller et al. Phys. Rev. Lett. 115, 247201 (2015)], and orbital excitations [L. Das et al. Phys. Rev. X 8, 011048 (2018)] in the multiorbital Mott insulator Ca${}_2$RuO${}_4$ are captured and good agreement is found with previous neutron and inelastic x-ray spectroscopic measurements. Furthermore, our results illustrate how a crystalline electric field-induced singlet ground state can support coherent longitudinal, or amplitude excitations, and transverse wavelike dynamics. We use this description to discuss mechanisms for accessing a nearby critical point.

18 pages, 8 figures

References in corpus (53)

• Correlated quantum phenomena in the strong spin-orbit regime
• Strong electronic correlations from Hund's coupling
• Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides
• Spin-Orbit Physics Giving Rise to Novel Phases in Correlated Systems: Iridates and Related Materials
• Amplitude / Higgs Modes in Condensed Matter Physics
• Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3
• 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${}_4$
• Amplitude `Higgs' mode in 2H-NbSe2 Superconductor
• The Higgs Mode in Disordered Superconductors Close to a Quantum Phase Transition
• Higgs mode and its decay in a two dimensional antiferromagnet
• Destruction of the Mott Insulating Ground State of Ca_2RuO_4 by a Structural Transition
• Spin-orbit coupling in $d^2$ ordered double perovskites
• Structural, orbital, and magnetic order in vanadium spinels
• Quantum and classical criticality in a dimerized quantum antiferromagnet
• From Mott insulator to ferromagnetic metal: a pressure study of Ca${}_2$RuO${}_4$
• Orbital ordering phenomena in $d$- and $f$-electron systems
• Orbital Dependent Phase Control in Ca2-xSrxRuO4
• Phase Transition, Longitudinal Spin Fluctuations and Scaling in a Two-Layer Antiferromagnet
• Orbital ordering transition in Ca${}_2$RuO${}_4$ observed with resonant x-ray diffraction
• Electron and orbital correlations in Ca_{2-x}Sr_{x}RuO_{4} probed by optical spectroscopy
• Raman scattering from Higgs mode oscillations in the two-dimensional antiferromagnet Ca${}_2$RuO${}_4$
• High pressure diffraction studies on Ca2RuO4
• Enhanced Pressure Dependence of Magnetic Exchange in A2+[V2]O4 Spinels Approaching the Itinerant Electron Limit
• Two-magnon excitations observed by neutron scattering in the two-dimensional spin-5/2 Heisenberg antiferromagnet Rb2MnF4
• Higgs amplitude mode in the vicinity of a $(2+1)$-dimensional quantum critical point
• Effective magnetic interactions in spin-orbit coupled $d^4$ Mott insulators
• Spin-Orbit-Induced Orbital Excitations in Sr2RuO4 and Ca2RuO4: A Resonant Inelastic X-ray Scattering Study
• From incommensurate correlations to mesoscopic spin resonance in YbRh2Si2
• Higgs amplitude mode in the vicinity of a $(2+1)$-dimensional quantum critical point: a nonperturbative renormalization-group approach
• Observation of spin-orbit excitations and Hund's multiplets in Ca${}_2$RuO${}_4$
• Generalized spin-wave theory: application to the bilinear-biquadratic model
• A Unique Crystal Structure of Ca${}_2$RuO${}_4$ in the Current Stabilized Semi-Metallic State
• 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
• Spin-Orbit Excitons in CoO
• Neutron scattering measurements of $dd$ and spin-orbit excitations below the Mott-Hubbard gap in CoO
• Nonequilibrium Orbital Transitions via Applied Electrical Current in Calcium Ruthenate
• Magnon dispersion in Ca2RuO4: impact of spin-orbit coupling and oxygen moments
• Disentangling orbital and spin exchange interactions for Co${}^{2+}$ on a rocksalt lattice
• Excitonic Magnetism at the intersection of Spin-orbit coupling and crystal-field splitting
• Lattice dynamics and the electron-phonon interaction in Ca${}_2$RuO${}_4$
• Ordered magnetism in the intrinsically decorated $j{}_{\mathrm{eff}}$ = $\frac{1}{2}$ $\alpha$-CoV${}_3$O${}_8$
• Raman scattering studies of spin, charge, and lattice dynamics in Ca_{2-x}Sr_{x}RuO_{4} (0 =< x < 0.2)
• Magnetic Fluctuations and the Spin-Orbit Interaction in Mott Insulating CoO
• Anharmonic magnon excitations in noncollinear and charge-ordered RbFe${}^{2+}$Fe${}^{3+}$F${}_6$
• SU($N$) spin-wave theory: Application to spin-orbital Mott insulators
• Persistence of antiferromagnetic order upon La substitution in the $4d^4$ Mott insulator Ca${}_2$RuO${}_4$
• Spontaneous decay of a soft optical phonon in the relaxor ferroelectric PbMg${}_{1/3}$Nb${}_{2/3}$O${}_3$
• Relaxing Kondo screened Kramers-doublets in CeRhSi${}_3$
• Stable Higgs mode in anisotropic quantum magnets
• Evidence for negative thermal expansion in the superconducting precursor phase SmFeAsO

Cited by in corpus (11)

• Orbital character of the spin-reorientation transition in TbMn${}_6$Sn${}_6$
• Two-dimensional ferromagnetic spin-orbital excitations in the honeycomb VI${}_3$
• Metastable antiphase boundary ordering in CaFe${}_2$O${}_4$
• Zeeman split Kramers doublets in spin-supersolid candidate Na${}_2$BaCo(PO${}_4$)${}_2$
• Spin-orbital correlations from complex orbital order in MgV${}_2$O${}_4$
• Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry
• Spin-orbit excitons and electronic configuration of the $5d^4$ insulator Sr${}_3$Ir${}_2$O${}_7$F${}_2$
• Excitonic transverse and amplitude fluctuations in the noncollinear and charge-ordered RbFe${}^{2+}$Fe${}^{3+}$F${}_6$
• Neutron scattering sum rules, symmetric exchanges, and helicoidal magnetism in MnSb${}_2$O${}_6$
• Anisotropic excitonic magnetism from discrete ${\mathrm{C}}_4$ symmetry in CeRhIn${}_5$
• Spin-orbital order and excitons in magnetoresistive HoBi