Antiferromagnetic excitonic insulator state in Sr3Ir2O7

Abstract

Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr3Ir2O7. By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges with the electronic continuum in between these high symmetry points and which decays upon heating concurrent with a decrease in the material’s resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr3Ir2O7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulator phase.

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

“…A bilayer-Hubbard model analysis revealed that a moderate correlation strength also leads to a giant magnon gap and suggested that the bilayer system in the intermediate regime could be the long-sought excitonic insulator. [235] 4.2. Enhancing and Manipulating J eff = 1/2 Pseudospin Fluctuations…”

Soft-Chemical Synthesis, Structure Evolution, and Insulator-to-Metal Transition in Pyrochlore-like λ-RhO2

“…In the presence of strong spin–orbit coupling (SOC), as expected in 4d and 5d transition metals, a d 5 electronic configuration can give rise to an effective j = 1/2 ground state with enhanced correlations, paving the way for exotic long-range macroscopic quantum states such as in α-RuCl 3 , − Sr 2 IrO 4 , − Sr 3 Ir 2 O 7 , − and A 2 IrO 3 (A = Li and Na). − Compounds containing tetravalent rhodium (Rh 4+ , 4d 5 ), which is isoelectronic to Ru 3+ and is the 4d analogue of Ir 4+ , should possess electronic and magnetic properties similar to those observed in other d 5 compounds. However, studies of the chemistry and physics of Rh 4+ in the solid-state phase space remain rather limited due to the relatively greater stability of the trivalent state (Rh 3+ , 4d 6 ).…”

Multidisciplinary Materials Research at Harbin Institute of Technology

“…As usual, it is an optically inactive dark exciton [18,19]. For an antiferromagnet, spin-triplet exciton has lower energy than spin-singlet one due to the exciton exchange interaction [9,11]. Accordingly, the ScNW would form a spin-triplet excitonic insulator when spontaneously generated excitons condense.…”

“…Its onset is accompanied by spontaneous symmetry breaking, may leading to interesting physical phenomena such as superfluidity [5,6] and electron ferroelectricity [7,8]. Intertwining with magnetic and topological order also gives rise to novel quantum states, including single-spin exciton condensates [9], spin-triplet excitonic insulators [6,10,11] and topological excitonic insulators [12][13][14][15][16][17]. However, to date, there is no universally accepted evidence that excitonic insulators exist in real-life materials.…”