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Published July 15, 2018 | Published + Accepted Version
Journal Article Open

Mott transition and collective charge pinning in electron doped Sr_2IrO_4

Abstract

We studied the in-plane dynamic and static charge conductivity of electron doped Sr_2IrO_4 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.

Additional Information

© 2018 American Physical Society. (Received 16 January 2018; revised manuscript received 14 May 2018; published 5 July 2018) We gratefully acknowledge discussions with C. Berthod and T. Giamarchi. This project was supported by the Swiss National Science Foundation (projects 200021-153405 and 200021-162628.). K.W. and N.B. contributed equally to this work.

Attached Files

Published - PhysRevB.98.045107.pdf

Accepted Version - 1806.06937

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August 19, 2023
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