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.

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Cited by in corpus (9)

• Universal relaxation in a holographic metallic density wave phase
• Strain-engineering of the charge and spin-orbital interactions in Sr2IrO4
• First-Principles Calculation of Spin and Orbital Contributions to Magnetically Ordered Moments in Sr${}_2$IrO${}_4$
• Charge Transfer and $dd$ excitations in AgF${}_2$
• Optical Signature of a Crossover from Mott- to Slater-type Gap in Sr${}_2$Ir${}_{1-x}$Rh${}_x$O${}_4$
• Magnetic field tuning of the valley population in the Weyl phase of Nd${}_2$Ir${}_2$O${}_7$
• Evolution of electronic structure of Ru-doped single-crystal iridiates, Sr${}_2$Ir${}_{1-x}$Ru${}_x$O${}_4$
• Orbital-Selective Spin-Orbit Mott Insulator in Fractional Valence Iridate La${}_3$Ir${}_3$O${}_{11}$
• Fermi surface and pseudogap in highly doped Sr${}_2$IrO${}_4$