Tunable 5d-t2g Mott State and Monoatomic Layer Two-Dimensional Electron Gas Realized in Spin–Orbit-Coupled SrIrO₃ through Heterostructuring

We employ density functional theory in combination with a correlation U correction to elucidate a complete charge transfer phenomenon between the interfacial Ti-t2g orbitals and Ir-t2g orbitals within spin–orbit-coupled (SrIrO3)m/(LaTiO3)1 superlattices. This charge transfer is driven by the interfacial polarity difference and oxygen octahedral distortion. Our investigation shows that hole doping of the LaTiO3 layer or increasing the number m of SrIrO3 layers offers an effective means to modulate the charge transfer and the electron occupation within the Jeff = 1/2 5d-bands of Ir atoms. This modulation leads to the emergence of various electronic states, including nonmagnetic band insulating (SrIrO3)1/(LaTiO3)1, ferromagnetic metallic (SrIrO3)1/(La1–xBaxTiO3)1, ferrimagnetic Mott insulating (SrIrO3)2/(LaTiO3)1, and ferrimagnetic metallic (SrIrO3)m/(LaTiO3)1 with m ≥ 3. Notably, we find that charge transfer and the two-dimensional electron gas phenomenon occur exclusively at the interfacial IrO2 monatomic layers of (SrIrO3)m/(LaTiO3)1, regardless of the thickness of the SrIrO3 layer. This behavior sharply contrasts with the characteristics of the LaAlO3/SrTiO3 system, where the 2DEG extends across multiple unit cells. Our research provides fresh insights into the unconventional 5d electronic structures of spin–orbit-coupled iridates, particularly those with less-explored fractionally occupied mixed valence state (Ir3.3+/Ir3.7+), suggesting their potential for application in nanoscale oxide electronic devices.