Electronic charges and electric potential at LaAlO3/SrTiO3 interfaces studied by core-level photoemission spectroscopy

We studied LaAlO3/SrTiO3 interfaces for varying LaAlO3 thickness by core-level photoemission spectroscopy. In Ti 2p spectra for conducting "n-type" interfaces, Ti3+ signals appeared, which were absent for insulating "p-type" interfaces. The Ti3+ signals increased with LaAlO3 thickness, but started well below the critical thickness of 4 unit cells for metallic transport. Core-level shifts with LaAlO3 thickness were much smaller than predicted by the polar catastrophe model. We attribute these observations to surface defects/adsorbates providing charges to the interface even below the critical thickness

Temperature Dependent Polarity Reversal in Au/Nb:SrTiO3 Schottky Junctions

We have observed temperature-dependent reversal of the rectifying polarity in Au/Nb:SrTiO3 Schottky junctions. By simulating current-voltage characteristics we have found that the permittivity of SrTiO3 near the interface exhibits temperature dependence opposite to that observed in the bulk, significantly reducing the barrier width. At low temperature, tunneling current dominates the junction transport due both to such barrier narrowing and to suppressed thermal excitations. The present results demonstrate that novel junction properties can be induced by the interface permittivity

Optical conductivity of the Kondo insulator YbB_12: Gap formation and low-energy excitations

Optical reflectivity experiments have been conducted on single crystals of the Kondo insulator YbB_12 in order to obtain its optical conductivity, \sigma(\omega). Upon cooling below 70 K, a strong supression of \sigma(\omega) is seen in the far-infrared region, indicating the opening of an energy gap of ~ 25 meV. This gap development is coincident with a rapid decrease in the magnetic susceptibility, which shows that the gap opening has significant influence on magnetic properties. A narrow, asymmetric peak is observed at ~40 meV in \sigma(\omega), which is attributed to optical transitions between the Yb 4f-derived states across the gap. In addition, a broad peak is observed at ~0.25 eV. This peak is attributed to transitions between Yb 4f-derived states and p-d band, and is reminiscent of similar peaks previously observed for rare-earth hexaborides.Comment: 4 pages, 4 figure

Two-Dimensional Confinement of 3d1 Electrons in LaTiO3/LaAlO3 Multilayers

We report spectroscopic ellipsometry measurements of the anisotropy of the interband transitions parallel and perpendicular to the planes of (LaTiO3)n(LaAlO3)5 multilayers with n = 1-3. These provide direct information about the electronic structure of the two-dimensional (2D) 3d^1 state of the Ti ions. In combination with LDA+U calculations, we suggest that 2D confinement in the TiO2 slabs lifts the degeneracy of the t_{2g} states leaving only the planar d_xy orbitals occupied. We outline that these multilayers can serve as a model system for the study of the t_{2g} 2D Hubbard model.Comment: 7 pages, 4 figures. Accepted for publication in Phys. Rev. Let

EXAMINATION OF THE TERRAIN EFFECT FOR TERRESTRIAL ALBEDO ESTIMATION VIA BRDF MODEL PARAMETERS

ISPRS Technical Commission III WG III/2, 10 Joint Workshop “Multidisciplinary Remote Sensing for Environmental Monitoring”, 12–14 March 2019, Kyoto, JapanIn this paper, we examine the effect of terrain on terrestrial albedo estimation. Terrestrial albedo is one of the most important parameters for understanding the global heat balance. The existing approach for estimating terrestrial albedo involves the estimation of model parameters of the bidirectional reflectance distribution function (BRDF) based on measurements obtained at different geometries. Then, narrowband albedos are estimated from the BRDF model parameters and the broadband albedo is finally estimated by narrowband-tobroadband conversion. Previous studies have not considered the terrain effect for generating the terrestrial albedo. Experiments using in situ measurements showed that the BRDF model, which transforms the geocoordinate of the reflectance of the shadowed terrain, generates the best accuracy. The improvement in the accuracy by the terrain effect correction is limited, and therefore further investigations using more in situ and simulated data are necessary for operational products

Characterization of the Schottky Barrier in SrRuO3/Nb:SrTiO3 Junctions

Internal photoemission spectroscopy was used to determine the Schottky barrier height in rectifying SrRuO3/Nb-doped SrTiO3 junctions for 0.01 wt % and 0.5 wt % Nb concentrations. Good agreement was obtained with the barrier height deduced from capacitance-voltage measurements, provided that a model of the nonlinear permittivity of SrTiO3 was incorporated in extrapolating the built-in potential, particularly for high Nb concentrations. Given the generic polarizability of perovskites under internal/external electric fields, internal photoemission provides a valuable independent probe of the interface electronic structure.Comment: 15 pages, 3 figure

Depletion of density of states near Fermi energy induced by disorder and electron correlation in alloys

We have performed high resolution photoemission study of substitutionally disordered alloys Cu-Pt, Cu-Pd, Cu-Ni, and Pd-Pt. The ratios between alloy spectra and pure metal spectra are found to have dips at the Fermi level when the residual resistivity is high and when rather strong repulsive electron-electron interaction is expected. This is in accordance with Altshuler and Aronov's model which predicts depletion of density of states at the Fermi level when both disorder and electron correlation are present.Comment: 1 tex file and 4 ps file

CHLOROPHYLL ESTIMATION OF LAKE WATER AND COASTAL WATER USING LANDSAT-8 AND SENTINEL-2A SATELLITE

Chlorophyll-a is an optically active compound (OAC) commonly used as a proxy for phytoplankton biomass in an aquatic environment. Retrieving the concentration of chlorophyll-a remains a challenge due to the presence of several OAC particularly in water bodies which are in proximity to the land-based activities. In this study, an effort has been made to estimate the chlorophyll-a concentration of both the freshwater Lake Biwa and the coastal water of Wakasa Bay in Japan. A spectral decomposition algorithm was used to determine the chlorophyll-a using the satellite images. The algorithm was applied to the satellite images from two different sensors namely Landsat-8/OLI and Sentinel-2A/MSI. The satellite-derived chlorophyll-a concentration for the lake and coastal water from two different sensors were compared to assess the performance of both the sensors. The accuracy of the chlorophyll-a results derived from the images was evaluated with the in-situ measurement data of the chlorophyll-a for the Lake Biwa and the coastal water of Wakasa Bay. Both satellite sensors appear to give the best results for the coastal water (R2 > 0.80) with an RMSE < 0.3 μg/L. However, slight underestimation of chlorophyll-a noted for the Landsat-8 image with an increase in chlorophyll-a concentration. For the lake water, Sentinel-2A results were relatively better (R2 > 0.70) than Landsat-8, with an RMSE of < 1.0 μg/L. The obtained results will be useful to evaluate the primary productivity of both freshwater and coastal water body

Unusual Pseudogap-like Features Observed in Iron Oxypnictide Superconductors

We have performed a temperature-dependent angle-integrated laser photoemission study of iron oxypnictide superconductors LaFeAsO:F and LaFePO:F exhibiting critical transition temperatures (Tc's) of 26 K and 5 K, respectively. We find that high-Tc LaFeAsO:F exhibits a temperature-dependent pseudogap-like feature extending over ~0.1 eV about the Fermi level at 250 K, whereas such a feature is absent in low-Tc LaFePO:F. We also find ~20-meV pseudogap-like features and signatures of superconducting gaps both in LaFeAsO:F and LaFePO:F. We discuss the possible origins of the unusual pseudogap-like features through comparison with the high-Tc cuprates