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We report magneto-transport properties of heterointerfaces between the Mott insulator LaTiO 3 and the band insulator SrTiO 3 in a delta-doping geometry. At low temperatures, we have found a strong nonlinearity in the magnetic field dependence of the Hall resistivity, which can be effectively controlled by varying the temperature and the electric field. We attribute this effect to multichannel conduction of interfacial charges generated by an electronic reconstruction. In particular, the formation of a highly mobile conduction channel revealed by our data is explained by the greatly increased dielectric permeability of SrTiO 3 at low temperatures, and its electric-field dependence reflects the spatial distribution of the quasi-two-dimensional electron gas.

We have synthesized epitaxial Sr 2 IrO 4 thin-films on various substrates and studied their electronic structures as a function of lattice-strain. Under tensile (compressive) strain, increased (decreased) Ir-O-Ir bond-angle is expected to result in increased (decreased) electronic bandwidth. However, we have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are shifted to higher (lower) energies under tensile (compressive) strain, indicating that the electronic-correlation energy is also affected by in-plane lattice-strain. The effective tuning of electronic structures under lattice-modification provides an important insight into the physics driven by the coexisting strong spin-orbit coupling and electronic correlation. PACS: 71.70.Ej, 72.80.Sk, 81.15 In this letter, we report on the growth and optical properties of Sr 2 IrO 4 (SIO-214) thin films. The in-plane lattice mismatches between SIO-214 and various oxide substrates can exert both tensile (+) and compressive (-) strains to films, as shown in Fig. 1(a). We find that the electronic structure of SIO-214 films are effectively altered by lattice strain, and we observe 3 shifted optical transitions (absorptions) between the J eff = 1/2 lower Hubbard band (LHB) and the J eff = 1/2 upper Hubbard band (UHB), and between the J eff = 3/2 band and the J eff = 1/2 UHB band. Our observations strongly suggest that not only the electronic bandwidth, but also the magnitude of the effective electronic correlation energy (U eff ), can be manipulated by lattice strain. Our results demonstrate that epitaxial SIO-214 thin films can be used as a model system to study the physics of coexisting strong electron correlation and strong spin-orbit coupling under lattice modification.We have used a custom-built, pulsed laser deposition system equipped with in-situ Table I. The epitaxial growth conditions are found to be the following: an oxygen partial pressure (P O2 ) of 10 mTorr, a substrate temperature of 700 °C, and a laser (KrF excimer, λ = 248 nm) fluence of 1.2 J/cm 2 . Figure 2 shows θ-2θ X-ray diffraction scans of the samples discussed herein. Well-defined 00l-peaks are present due to the films' 00l-orientation along the perpendicular to the substrates. The full widths at half maximum in rocking-curve scans of the 00l peaks are all less than 0.05°, which confirms the high crystallinity of the films. Note that the thin films' 0012-peaks are shifted to low angles as the substrate lattice parameters decrease (from GSO to LAO). This behavior is consistent with the schematic diagrams in Fig. 1(b), since elongated (contracted) out-of-plane lattice parameters are expected as compressive (tensile) in-plane strain is exerted on thin films. 4Figure 3(a) shows X-ray reciprocal space maps, which reveal important information about both the in-plane and the out-of-plane lattice parameters of the SIO-214 thin films near the 332-reflection (103-reflection) of orthorhombic (pseudo-cubic) substrates. The 1118-peaks from the thin films are clearly observed, and are...

We investigated the temperature-dependent evolution of the electronic structure of the J eff = 1 2 Mott insulator Sr 2 IrO 4 using optical spectroscopy. The optical conductivity spectra ͑ ͒ of this compound has recently been found to exhibit two d-d transitions associated with the transition between the J eff = 1 2 and J eff = 3 2 bands due to the cooperation of the electron correlation and spin-orbit coupling. As the temperature increases, the two peaks show significant changes resulting in a decrease in the Mott gap. The experimental observations are compared with the results of first-principles calculation in consideration of increasing bandwidth. We discuss the effect of the temperature change in the electronic structure of Sr 2 IrO 4 in terms of local lattice distortion, excitonic effect, electron-phonon coupling, and magnetic ordering.