Spin-polaron ladder spectrum of the spin-orbit-induced Mott insulator Sr${}_2$IrO${}_4$ probed by scanning tunneling spectroscopy

Abstract

The motion of doped electrons or holes in an antiferromagnetic lattice with strong on-site Coulomb interactions touches one of the most fundamental open problems in contemporary condensed matter physics. The doped charge may strongly couple to elementary spin excitations resulting in a dressed quasiparticle which is subject to confinement. This 'spin-polaron' possesses internal degrees of freedom with a characteristic 'ladder' excitation spectrum. Despite its fundamental importance for understanding high-temperature superconductivity, clear experimental spectroscopic signatures of these internal degrees of freedom are scarce. Here we present scanning tunneling spectroscopy results of the spin-orbit-induced Mott insulator Sr${}_2$IrO${}_4$. Our spectroscopy data reveal distinct shoulder-like features for occupied and unoccupied states beyond a measured Mott gap of $\Delta \approx 620$~meV. Using the self-consistent Born approximation we assign the anomalies in the unoccupied states to the spin-polaronic ladder spectrum with excellent quantitative agreement and estimate the Coulomb repulsion $U$ = 2.05 ...2.28 eV in this material. These results confirm the strongly correlated electronic structure of this compound and underpin the previously conjectured paradigm of emergent unconventional superconductivity in doped Sr${}_2$IrO${}_4$.

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Cited by in corpus (2)

• Atomic-scale fragmentation and collapse of antiferromagnetic order in a doped Mott insulator
• Percolative Mott insulator-metal transition in doped Sr${}_2$IrO${}_4$