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arXiv · 1806.06937

Mott transition and collective charge pinning in electron doped Sr2IrO4

K. Wang·N. Bachar·J. Teyssier·W. Luo·C. W. Rischau·G. Scheerer·A. de la Torre·R. S. Perry·F. Baumberger·D. van der Marel
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Abstract

We studied the in-plane dynamic and static charge conductivity of electron doped Sr2IrO4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott-gap of 0.55 eV. Upon substitution of 2% La per formula unit the Mott-gap is suppressed except in a small fraction of the material (15%) where the gap survives, and overall the material remains insulating. Instead of a zero energy mode (or Drude peak) we observe a soft collective mode (SCM) with a broad maximum at 40 meV. Doping to 10% increases the strength of the SCM, and a zero-energy mode occurs together with metallic DC conductivity. Further increase of the La substitution doesn't change the spectral weight integral up to 3 eV. It does however result in a transfer of the SCM spectral weight to the zero-energy mode, with a corresponding reduction of the DC resistivity for all temperatures from 4 to 300 K. The presence of a zero-energy mode signals that at least part of the Fermi surface remains ungapped at low temperatures, whereas the SCM appears to be caused by pinning a collective frozen state involving part of the doped electrons.

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K. Wang, N. Bachar, J. Teyssier, W. Luo, C. W. Rischau, G. Scheerer, A. de la Torre, R. S. Perry, F. Baumberger, D. van der Marel. 2018-06-18. Mott transition and collective charge pinning in electron doped Sr2IrO4. https://doi.org/10.1103/physrevb.98.045107

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