Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity.

In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e(-) from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥ 4 unit cells of LaAlO3) there is indeed a ~0.5e(-) transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤ 3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e(-) is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.

Self-consistent iteration procedure in analyzing reflectivity and spectroscopic ellipsometry data of multilayered materials and their interfaces.

For multilayered materials, reflectivity depends on the complex dielectric function of all the constituent layers, and a detailed analysis is required to separate them. Furthermore, for some cases, new quantum states can occur at the interface which may change the optical properties of the material. In this paper, we discuss various aspects of such analysis, and present a self-consistent iteration procedure, a versatile method to extract and separate the complex dielectric function of each individual layer of a multilayered system. As a case study, we apply this method to LaAlO3/SrTiO3 heterostructure in which we are able to separate the effects of the interface from the LaAlO3 film and the SrTiO3 substrate. Our method can be applied to other complex multilayered systems with various numbers of layers.

Bioequivalence study of 2 formulations of film-coated tablets containing a fixed dose combination of bisoprolol fumarate 5 mg and hydrochlorothiazide 6.25 mg in healthy subjects.

BACKGROUND: The present study was conducted to compare the bioavailability of 2 formulations of fixed-dose combination of bisoprolol fumarate 5 mg and hydrochlorotiazide (HCT) 6.25 mg film-coated tablet (test and reference formulations). METHODS: This study was a randomized, single-blind, 2-period, 2-sequence cross-over study which included 18 healthy adult male and female subjects under fasting condition. The pharmacokinetic parameters, AUCt, AUCinf, Cmax, tmax, and t½ were determined based on the concentrations of bisoprolol (CAS 66722-44-9) and HCT (CAS 58-93-5), using ultra-performance liquid chromatography with tandem mass spectrometer detector (UPLC-MS/MS). In each of the 2 study periods (with a washout of 1 week) a single dose of test or reference product was administered. RESULTS: The geometric mean ratios (90% CI) of the test drug/reference drug for bisoprolol were 97.22% (93.75-100.83%) for AUCt(0-48), 97.20% (93.97-100.54%) for AUCinf, and 100.36% (93.83-107.34%) for Cmax; while those for HCT were 93.22% (84.72-102.57%), 93.39% (85.43-102.10%) and 99.39% (85.45-115.61%), for AUCt(0-24), AUCinf, and Cmax, respectively. The differences between the test and reference drug products for tmax values of bisoprolol as well as t½ values of both bisoprolol and hydrochlorothiazide were not statistically significant; yet, the difference was statistically significant for the tmax values of hydrochlorothiazide. There was no adverse event encountered during this bioequivalence test. MAJOR CONCLUSION: It was concluded that the 2 formulations of fixed dose combination of bisoprolol fumarate 5 mg and hydrochlorotiazide (HCT) 6.25 mg film-coated tablet (the test and reference products) were bioequivalent.

Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti1-xTaxO2 (x~0.05) thin films.

We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti(1-x)Ta(x)O(2) (x∼0.05) thin films grown by pulsed laser deposition on LaAlO(3) substrates. Rutherford backscattering spectrometry (RBS), X-ray diffraction, proton-induced X-ray emission, X-ray absorption spectroscopy (XAS) and time-of-flight secondary-ion mass spectrometry indicated negligible magnetic contaminants in the films. The presence of FM with concomitant large carrier densities was determined by a combination of superconducting quantum interference device magnetometry, electrical transport measurements, soft X-ray magnetic circular dichroism (SXMCD), XAS and optical magnetic circular dichroism, and was supported by first-principles calculations. SXMCD and XAS measurements revealed a 90 per cent contribution to FM from the Ti ions, and a 10 per cent contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites, though carrier activation was only 50 per cent at 5 per cent Ta concentration, implying compensation by cationic defects. The role of the Ti vacancy (V(Ti)) and Ti(3+) was studied via XAS and X-ray photoemission spectroscopy, respectively. It was found that, in films with strong FM, the V(Ti) signal was strong while the Ti(3+) signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localized magnetic moments, V(Ti) sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to FM in wide-band-gap semiconducting oxides without any magnetic elements.

Room-temperature ferromagnetism of Cu-doped ZnO films probed by soft X-ray magnetic circular dichroism.

We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu2+ ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V(O)) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic "indirect double-exchange" model, in which alignments of localized large moments of Cu in the vicinity of the V(O) are mediated by the large-sized vacancy orbitals.

Experimental proof of a structural origin for the shadow fermi surface of Bi2Sr2CaCu2O8+delta.

By combining surprising new results from a full polarization analysis of nodal angle-resolved photoemission data from pristine and modulation-free Bi(2)Sr(2)CaCu(2)O(8+delta) with structural information from LEED and ab initio one-step photoemission simulations, we prove that the shadow Fermi surface in these systems is of structural origin, being due to orthorhombic distortions from tetragonal symmetry present both in surface and bulk. Consequently, one of the longest standing open issues in the investigation of the Fermi surface of these widely studied systems finally meets its resolution.