Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3 (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. Here, we report that highquality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin films grown under the kinetically controlled conditions, down to ca. 16 nm in thickness, exhibit both enhanced conductivity and TC as compared to bulk values, due to their improved stoichiometry and a strain-mediated increase of the bandwidth of Ru 4d electrons. This result provides a direction for enhancing the physical properties of PLE-grown thin films and paves a way for improved device applications. I (a.u.) (deg.) FWHM = 0.06

We have investigated the electronic and optical properties of (Sr1-xCax)2IrO4 ( = 0 -0.375) and (Sr1-yBay)2IrO4 ( = 0 -0.375) epitaxial thin-films, in which the bandwidth is systematically tuned via chemical substitutions of Sr ions by Ca and Ba. Transport measurements indicate that the thin-film series exhibits insulating behavior, similar to the eff = 1/2 spin-orbit Mott insulator Sr2IrO4. As the average A-site ionic radius increases from (Sr1-xCax)2IrO4 to (Sr1-yBay)2IrO4, optical conductivity spectra in the near-infrared region shift to lower energies, which cannot be explained by the simple picture of well-separated eff = 1/2 and eff = 3/2 bands. We suggest that the two-peak-like optical conductivity spectra of the layered iridates originates from the overlap between the optically-forbidden spin-orbit exciton and the inter-site optical transitions within the eff = 1/2 band. Our experimental results are consistent with this interpretation as implemented by a multi-orbital Hubbard model calculation: namely, incorporating a strong Fano-like coupling between the spin-orbit exciton and inter-site d-d transitions within the eff = 1/2 band.

We report that epitaxial Sr2IrO4 thin-films can be selectively grown using pulsed laser deposition (PLD). Due to the competition between the Ruddlesden-Popper phases of strontium iridates (Srn+1IrnO3n+1), conventional PLD methods often result in mixed phases of Sr2IrO4 (n = 1), Sr3Ir2O7 (n = 2), and SrIrO3 (n = ∞). We have discovered that reduced PLD plume dimensions and slow deposition rates are the key for stabilizing pure Sr2IrO4 phase thin-films, identified by real-time in-situ monitoring of their optical spectra. The slow film deposition results in a thermodynamically stable TiO2\\SrO\IrO2\SrO\SrO configuration at an interface rather than TiO2\\SrO\SrO\IrO2\SrO between a TiO2-teminated SrTiO3 substrate and a Sr2IrO4 thin film, which is consistent with other layered oxides grown by molecular beam epitaxy. Our approach provides an effective method for using PLD to achieve pure phase thin-films of layered materials that are susceptible to several energetically competing phases. PACS: 68.37.Ma, 71.70.Ej, 81.15.Fg,2 With the advent of physical vapor deposition techniques such as pulsed laser deposition (PLD), complex oxide thin-films have been extensively studied in applied physics research. Thin-film research offers not only controlled tunability over lattice-symmetry (by strain), dimensionality, and interfacial coupling, but also an important advance for device applications. In particular, PLD has been very successful in synthesizing complex oxide thin-films such as high-Tc superconducting cuprates, e.g., In this letter, we report that epitaxial thin-films of Sr2IrO4 phase can be selectively grown among the Ruddlesden-Popper (R-P) (Srn+1IrnO3n+1) series by pulsed laser deposition (PLD) with real-time monitoring of in-situ optical spectroscopic ellipsometry. Despite the use of a Sr2IrO4 polycrystal as a PLD target (i.e., source material), epitaxial thin-films often exhibit various phases even under nearly identical growth conditions. Figure 1 (a) shows the powder x-ray diffraction 3 (XRD) of our Sr2IrO4 polycrystalline target, which indicates a pure phase of Sr2IrO4 with no secondary or mixed phases. When the plume size is reduced ( Fig. 1 (b1)) by using a smaller laser spot size of approximately 0.25 mm 2 , we have observed that high-quality Sr2IrO4 thin-films are grown, as evident in the XRD scan presented in Fig. 1 (b2). However, conventional PLD (with a laser spot size of about 0.75 mm 2 and a large plume, as shown in Fig. 1 (c1)) often produces SrIrO3-phase dominant thin films, as shown in the XRD scan of Fig. 1 (c2). A photograph of the two laser spot sizes is presented in Fig. S1. Note that these samples are not pure SrIrO3 thin films but contain other R-P phases as evident from XRD and microscopic characterizations such as transmission electron microscopy (data not shown).In order to understand this observation systematically, we have synthesized a test sample by using various laser beam spot sizes on the target. (See Ref. 12 regarding the technical details on controlling the laser spot sizes b...

We have synthesized and investigated the heterointerfaces of KTaO3 (KTO) and GdScO3 (GSO), which are both polar complex-oxides along the pseudo-cubic [001] direction. Since their layers have the same, conflicting net charges at interfaces, i.e. KO(-1)/ScO2(-1) or TaO2(+1)/GdO(+1), forming the heterointerface of KTO/GSO should be forbidden due to strong Coulomb repulsion, the so-called polarity conflict. However, we have discovered that atomic reconstruction occurs at the heterointerfaces between KTO thin-films and GSO substrates, which effectively alleviates the polarity conflict without destroying the heteroepitaxy.Our result demonstrates one of the important ways to create artificial heterostructures from polar complex-oxides.

Low threshold 1.3 μm InGaAsP/InP double heterostructure lasers were fabricated using all gas source chemical beam epitaxy (CBE). Gas source doping of n- and p-type InP and InGaAs was successfully achieved using tetraethyltin and diethylzinc. The minimum threshold current density (Jth) for a 1800 μm cavity length laser was 680 A/cm−2. This is lowest Jth value reported for CBE grown double heterostructure lasers at 1.3 μm. These lasers exhibited an internal quantum efficiency (ηi) and internal loss (αi) of 51% and 16 cm−1, respectively. The temperature dependence of the threshold current is described by a single exponential T0 of 51 K.