Jixia Dai, Eduardo Calleja, Gang Cao, Kyle McElroy
We present scanning tunneling microscopy and spectroscopy experiments on the novel $J_\mathrm{eff}=1/2$ Mott insulator Sr$_2$IrO$_4$. Local density of states (LDOS) measurements show an intrinsic insulating gap of 620 meV that is asymmetric about $E_\mathrm{F}$ and is larger than previously reported values. The size of this gap strongly suggests that Sr$_2$IrO$_4$ is a Mott rather than Slater insulator. In addition, we found a small number of native defects which create in-gap spectral weight. Atomically resolved LDOS measurements on and off the defects naturally explain why such a large gap in this 5d system has not been seen by other probes. The extended nature of the 5d electrons and the insulating character of Sr$_2$IrO$_4$ together facilitate the vulnerability of this gap.
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http://arxiv.org/abs/1303.3688
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