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arXiv · 1802.10028

Spin-polaron ladder spectrum of the spin-orbit-induced Mott insulator Sr$_2$IrO$_{4}$ probed by scanning tunneling spectroscopy

Jose M. Guevara·Zhixiang Sun·Ekaterina M. Pärschke·Steffen Sykora·Kaustuv Manna·Johannes Schoop·Andrey Maljuk·Sabine Wurmehl·Jeroen van den Brink·Bernd Büchner·Christian Hess
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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 $Δ\approx620$~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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Jose M. Guevara, Zhixiang Sun, Ekaterina M. Pärschke, Steffen Sykora, Kaustuv Manna, Johannes Schoop, Andrey Maljuk, Sabine Wurmehl, Jeroen van den Brink, Bernd Büchner, Christian Hess. 2019-03-18. Spin-polaron ladder spectrum of the spin-orbit-induced Mott insulator Sr$_2$IrO$_{4}$ probed by scanning tunneling spectroscopy. https://doi.org/10.1103/physrevb.99.121114

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