Spin-gap and two-dimensional magnetic excitations in Sr2IrO4

Abstract

Time-of-flight inelastic neutron scattering measurements on Sr2IrO4 single crystals were performed to access the spin Hamiltonian in this canonical Jeff=1/2 spin-orbital Mott insulator. The momentum of magnetic scattering at all inelastic energies measured is revealed to be L independent, indicative of idealized two-dimensional in-plane correlations. We model the in-plane energy and momentum dependence of the excitations, that were measured up to ∼80 meV, and define a spin gap of 0.6(1) meV. Collectively, the results indicate that despite the strongly spin-orbit entangled isospins, an isotropic two-dimensional S=1/2 Heisenberg model Hamiltonian accurately describes the magnetic interactions, confirming a robust analogy with unconventional superconducting cuprates.