Mott transition and collective charge pinning in electron doped Sr2IrO4

Understand

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.