Mott transition and collective charge pinning in electron doped Sr2IrO4
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.
- Publication:
-
Physical Review B
- Pub Date:
- July 2018
- DOI:
- 10.1103/PhysRevB.98.045107
- arXiv:
- arXiv:1806.06937
- Bibcode:
- 2018PhRvB..98d5107W
- Keywords:
-
- Condensed Matter - Strongly Correlated Electrons
- E-Print:
- Physical Review B 98, 045107 (2018)