Spin-polaron ladder spectrum of the spin-orbit-induced Mott insulator Sr 2 IrO 4 probed by scanning tunneling spectroscopy

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 quas...

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Bibliographic Details
Published in:Physical review. B 2019-03, Vol.99 (12), Article 121114
Main Authors: Guevara, Jose M., Sun, Zhixiang, Pärschke, Ekaterina M., Sykora, Steffen, Manna, Kaustuv, Schoop, Johannes, Maljuk, Andrey, Wurmehl, Sabine, van den Brink, Jeroen, Büchner, Bernd, Hess, Christian
Format: Article
Language:English
Subjects:
Anomalies
Antiferromagnetism
Born approximation
Condensed matter physics
Degrees of freedom
Electronic structure
Excitation spectra
High temperature
Polarons
Scanning
Scanning tunneling microscopy
Spectroscopy
Spectrum analysis
Unconventional superconductivity
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Summary: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 ≈ 620 meV. Using the self-consistent Born approximation we assign the anomalies in the unoccupied states to the spin-polaron 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 .
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.99.121114