Abstract
We report on infrared spectroscopy experiments on the electronic response in (Sr1−xLax)2IrO4 (x = 0, 0.021, and 0.067). Our data show that electron doping induced by La substitution leads to an insulator-to-metal transition. The evolution of the electronic structure across the transition reveals the robustness of the strong electronic correlations against the electron doping. The conductivity data of the metallic compound show the signature of the pseudogap that bears close similarity to the analogous studies of the pseudogap in the underdoped cuprates. While the low energy conductivity of the metallic compound is barely frequency dependent, the formation of the pseudogap is revealed by the gradual suppression of the featureless conductivity below a threshold frequency of about 17 meV. The threshold structure develops below about 100 K which is in the vicinity of the onset of the short-range antiferromagnetic order. Our results demonstrate that the electronic correlations play a crucial role in the anomalous charge dynamics in the (Sr1−xLax)2IrO4 system.
Highlights
IntroductionThe magnetic excitation spectra of Sr2IrO4 is well described by antiferromagnetic Heisenberg model with a pseudospin 1/2 on a quasi-two-dimensional square lattice[3, 4]
We report on infrared spectroscopy experiments on the electronic response in (Sr1−xLax)2IrO4 (x = 0, 0.021, and 0.067)
Two peaks at about 0.5 eV and 1 eV labeled as α and β correspond to the transitions from the lower Hubbard band (LHB) to upper Hubbard band (UHB) and from the Jeff = 3/2 bands to the Jeff = 1/2 UHB, respectively[1, 24, 25]
Summary
The magnetic excitation spectra of Sr2IrO4 is well described by antiferromagnetic Heisenberg model with a pseudospin 1/2 on a quasi-two-dimensional square lattice[3, 4] Given these similarities, theoretical studies suggest that a singlet d-wave or a triplet p-wave high-temperature superconductivity could emerge in electron or hole-doped Sr2IrO4, respectively[5,6,7]. Scanning tunneling microscopy/spectroscopy (STM/STS) studies demonstrated that the nanoscale electronic phase separation occurred upon electron doping and the pseudogap states emerged around the dopant atoms[11, 12, 15] Despite these observations, the origin of the pseudogap in this Jeff = 1/2 cuprate analog remains elusive. To the best of our knowledge, no infrared spectroscopic study in carrier-doped Sr2IrO4 has been reported before
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