Superconducting NdEuNiO thin films using in situ synthesis.

We report on superconductivity in NdEuNiO using Eu as a 4f dopant of the parent NdNiO infinite-layer compound. We use an all-in situ molecular beam epitaxy reduction process to achieve the superconducting phase, providing an alternate method to the ex situ CaH reduction process to induce superconductivity in the infinite-layer nickelates. The NdEuNiO samples exhibit a step-terrace structure on their surfaces, have a onset of 21 K at = 0.

Heteroepitaxial Control of Fermi Liquid, Hund Metal, and Mott Insulator Phases in Single-Atomic-Layer Ruthenates.

Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities, and great efforts have been made to manipulate interfacial electronic phases. However, realizing such phases is often hampered by the inability to directly access the electronic structure information; most correlated interfacial phenomena appear within a few atomic layers from the interface. Here, atomic-scale epitaxy and photoemission spectroscopy are utilized to realize the interface control of correlated electronic phases in atomic-scale ruthenate-titanate heterostructures.

High-order replica bands in monolayer FeSe/SrTiO revealed by polarization-dependent photoemission spectroscopy.

The mechanism of the enhanced superconductivity in monolayer FeSe/SrTiO has been enthusiastically studied and debated over the past decade. One specific observation has been taken to be of central importance: the replica bands in the photoemission spectrum. Although suggestive of electron-phonon interaction in the material, the essence of these spectroscopic features remains highly controversial.

Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal.

Titanium monoxide (TiO), an important member of the rock salt 3d transition-metal monoxides, has not been studied in the stoichiometric single-crystal form. It has been challenging to prepare stoichiometric TiO due to the highly reactive Ti We adapt a closely lattice-matched MgO(001) substrate and report the successful growth of single-crystalline TiO(001) film using molecular beam epitaxy. This enables a first-time study of stoichiometric TiO thin films, showing that TiO is metal but in proximity to Mott insulating state.

Tuning spin excitations in magnetic films by confinement.

Spin excitations of magnetic thin films are the founding element for magnetic devices in general. While spin dynamics have been extensively studied in bulk materials, the behaviour in mesoscopic films is less known due to experimental limitations. Here, we employ resonant inelastic X-ray scattering to investigate the spectrum of spin excitations in mesoscopic Fe films, from bulk-like films down to three unit cells.

Stabilization of Competing Ferroelectric Phases of HfO_{2} under Epitaxial Strain.

Hafnia (HfO_{2})-based thin films have promising applications in nanoscale electronic devices due to their robust ferroelectricity and integration with silicon. Identifying and stabilizing the ferroelectric phases of HfO_{2} have attracted intensive research interest in recent years. In this work, first-principles calculations on (111)-oriented HfO_{2} are used to discover that imposing an in-plane shear strain on the metastable tetragonal phase drives it to a polar phase.

Strong Orbital Polarization in a Cobaltate-Titanate Oxide Heterostructure.

Through a combination of experimental measurements and theoretical modeling, we describe a strongly orbital-polarized insulating ground state in an (LaTiO_{3})_{2}/(LaCoO_{3})_{2} oxide heterostructure. X-ray absorption spectra and ab initio calculations show that an electron is transferred from the titanate to the cobaltate layers. The charge transfer, accompanied by a large octahedral distortion, induces a substantial orbital polarization in the cobaltate layer of a size unattainable via epitaxial strain alone.

Integration of sputter-deposited multiferroic CoFeO-BiFeO nanocomposites on conductive LaSrMnO electrodes.

The structure, magnetic and ferroelectric properties of sputtered epitaxial CoFeO-BiFeO (CFO-BFO) nanocomposite thin films grown on LaSrMnO (LSMO) layers on (001) oriented SrTiO (STO) substrates and on STO-buffered Si are described. The as-grown LSMO thin films were smooth and poorly conductive but the resistivity was reduced and the surfaces roughened after annealing. Cosputtered CFO and BFO on STO formed vertically aligned nanostructures consisting of epitaxial spinel CFO pillars within a perovskite BFO matrix, but the rough surface of the annealed LSMO film promoted additional CFO pillar orientations.

Controlling Mobility in Perovskite Oxides by Ferroelectric Modulation of Atomic-Scale Interface Structure.

Coherent and epitaxial interfaces permit the realization of electric field driven devices controlled by atomic-scale structural and electronic effects at interfaces. Compared to conventional field effect devices where channel conductivity is modulated by carrier density modification, the propagation of atomic-scale distortions across an interface can control the atomic scale bonding, interatomic electron tunneling rates and thus the mobility of the channel material. We use first-principles theory to design an atomically abrupt epitaxial perovskite heterostructure involving an oxide ferroelectric (PbZrTiO) and conducting oxide channel (LaNiO) where coupling of polar atomic motions to structural distortions can induce large, reversible changes in the channel mobility.

Single Atomic Layer Ferroelectric on Silicon.

A single atomic layer of ZrO exhibits ferroelectric switching behavior when grown with an atomically abrupt interface on silicon. Hysteresis in capacitance-voltage measurements of a ZrO gate stack demonstrate that a reversible polarization of the ZrO interface structure couples to the carriers in the silicon. First-principles computations confirm the existence of multiple stable polarization states and the energy shift in the semiconductor electron states that result from switching between these states.

Electron-beam-induced-current and active secondary-electron voltage-contrast with aberration-corrected electron probes.

The ability to map out electrostatic potentials in materials is critical for the development and the design of nanoscale electronic and spintronic devices in modern industry. Electron holography has been an important tool for revealing electric and magnetic field distributions in microelectronics and magnetic-based memory devices, however, its utility is hindered by several practical constraints, such as charging artifacts and limitations in sensitivity and in field of view. In this article, we report electron-beam-induced-current (EBIC) and secondary-electron voltage-contrast (SE-VC) with an aberration-corrected electron probe in a transmission electron microscope (TEM), as complementary techniques to electron holography, to measure electric fields and surface potentials, respectively.

Electron-beam-induced-current and active secondary-electron voltage-contrast with aberration-corrected electron probes.

The ability to map out electrostatic potentials in materials is critical for the development and the design of nanoscale electronic and spintronic devices in modern industry. Electron holography has been an important tool for revealing electric and magnetic field distributions in microelectronics and magnetic-based memory devices, however, its utility is hindered by several practical constraints, such as charging artifacts and limitations in sensitivity and in field of view. In this article, we report electron-beam-induced-current (EBIC) and secondary-electron voltage-contrast (SE-VC) with an aberration-corrected electron probe in a transmission electron microscope (TEM), as complementary techniques to electron holography, to measure electric fields and surface potentials, respectively.

Correction: A narrow amide I vibrational band observed by sum frequency generation spectroscopy reveals highly ordered structures of a biofilm protein at the air/water interface.

Correction for 'A narrow amide I vibrational band observed by sum frequency generation spectroscopy reveals highly ordered structures of a biofilm protein at the air/water interface' by Zhuguang Wang et al., Chem. Commun.

A narrow amide I vibrational band observed by sum frequency generation spectroscopy reveals highly ordered structures of a biofilm protein at the air/water interface.

We characterized BslA, a bacterial biofilm protein, at the air/water interface using vibrational sum frequency generation spectroscopy and observed one of the sharpest amide I bands ever reported. Combining methods of surface pressure measurements, thin film X-ray reflectivity, and atomic force microscopy, we showed extremely ordered BslA at the interface.

Reversible modulation of orbital occupations via an interface-induced polar state in metallic manganites.

The breaking of orbital degeneracy on a transition metal cation and the resulting unequal electronic occupations of these orbitals provide a powerful lever over electron density and spin ordering in metal oxides. Here, we use ab initio calculations to show that reversibly modulating the orbital populations on Mn atoms can be achieved at ferroelectric/manganite interfaces by the presence of ferroelectric polarization on the nanoscale. The change in orbital occupation can be as large as 10%, greatly exceeding that of bulk manganites.

Interface-induced nonswitchable domains in ferroelectric thin films.

Engineering domains in ferroelectric thin films is crucial for realizing technological applications including non-volatile data storage and solar energy harvesting. Size and shape of domains strongly depend on the electrical and mechanical boundary conditions. Here we report the origin of nonswitchable polarization under external bias that leads to energetically unfavourable head-to-head domain walls in as-grown epitaxial PbZr(0.

Tuning the structure of nickelates to achieve two-dimensional electron conduction.

Metallic electronic transport in nickelate heterostructures can be induced and confined to two dimensions (2D) by controlling the structural parameters of the nickel-oxygen planes.

Active silicon integrated nanophotonics: ferroelectric BaTiO₃ devices.

The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric BaTiO3 thin films on the ubiquitous silicon-on-insulator (SOI) platform.

Modifying the electronic orbitals of nickelate heterostructures via structural distortions.

We describe a general materials design approach that produces large orbital energy splittings (orbital polarization) in nickelate heterostructures, creating a two-dimensional single-band electronic surface at the Fermi energy. The resulting electronic structure mimics that of the high temperature cuprate superconductors. The two key ingredients are (i) the construction of atomic-scale distortions about the Ni site via charge transfer and internal electric fields, and (ii) the use of three-component (tricomponent) superlattices to break inversion symmetry.