F. Pfaff

Dimensionality-tuned electronic structure of nickelate superlattices explored by soft-x-ray angle-resolved photoelectron spectroscopy

The electronic and magnetic properties of epitaxial LaNiO3/LaAlO3 superlattices can be tuned by layer thickness and substrate-induced strain. Here, we report on direct measurements of the k-space-resolved electronic structure of buried nickelate layers in superlattices under compressive strain by soft x-ray photoemission. After disentangling strong extrinsic contributions to the angle-dependent signal caused by photoelectron diffraction, we are able to extract Fermi surface information from our data. We find that with decreasing LaNiO3 thickness down to two unit cells (2 uc) quasiparticle coherence becomes strongly reduced, in accord with the dimension-induced metal-to-insulator transition seen in transport measurements. Nonetheless, on top of a strongly incoherent background a residual Fermi surface can be identified in the 2 uc superlattice whose nesting properties are consistent with the spin-density wave (SDW) instability recently reported. The overall behavior of the Ni 3d spectra and the absence of a complete gap opening indicate that the SDW phase is dominated by strong order parameter fluctuations.

Monitoring non-pseudomorphic epitaxial growth of spinel/perovskite oxide heterostructures by reflection high-energy electron diffraction

Pulsed laser deposition of spinel γ-Al2O3 thin films on bulk perovskite SrTiO3 is monitored by high-pressure reflection high-energy electron diffraction (RHEED). The heteroepitaxial combination of two materials with different crystal structures is found to be inherently accompanied by a strong intensity modulation of bulk diffraction patterns from inelastically scattered electrons, which impedes the observation of RHEED intensity oscillations. Avoiding such electron surface-wave resonance enhancement by de-tuning the RHEED geometry allows for the separate observation of the surface-diffracted specular RHEED signal and thus the real-time monitoring of sub-unit cell two-dimensional layer-by-layer growth. Since these challenges are essentially rooted in the difference between film and substrate crystal structure, our findings are of relevance for the growth of any heterostructure combining oxides with different crystal symmetry and may thus facilitate the search for novel oxide heterointerfaces.

Microscopic origin of the mobility enhancement at a spinel/perovskite oxide heterointerface revealed by photoemission spectroscopy

The spinel/perovskite heterointerface

Domain matching epitaxy of BaBiO3 on SrTiO3 with structurally modified interface

\ensuremath{\gamma}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}/{\mathrm{SrTiO}}_{3}

Surface-interface coupling in an oxide heterostructure: Impact of adsorbates onLaAlO3/SrTiO3

hosts a two-dimensional electron system (2DES) with electron mobilities exceeding those in its all-perovskite counterpart

Band bending and alignment at the spinel/perovskite γ−Al2O3/SrTiO3 heterointerface

{\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}

Bulk nature of layered perovskite iridates beyond the Mott scenario: An approach from a bulk-sensitive photoemission study

by more than an order of magnitude, despite the abundance of oxygen vacancies which act as electron donors as well as scattering sites. By means of resonant soft x-ray photoemission spectroscopy and ab initio calculations, we reveal the presence of a sharply localized type of oxygen vacancies at the very interface due to the local breaking of the perovskite symmetry. We explain the extraordinarily high mobilities by reduced scattering resulting from the preferential formation of interfacial oxygen vacancies and spatial separation of the resulting 2DES in deeper

New type of in-gap states at a spinel/perovskite interface: combined resonant soft x-ray photoemission spectroscopy and first-principles study.

{\mathrm{SrTiO}}_{3}

Spin–Orbit–Coupling–Induced jeff States in Perovskite Iridates Studied by Photoemission Spectroscopy

layers. Our findings comply with transport studies and pave the way towards defect engineering at interfaces of oxides with different crystal structures.

Direct k-space mapping of the electronic structure in oxide-oxide interfaces

The perovskite BaBiO3 (BBO) is a versatile oxide parent material which displays superconductivity upon p-doping, while n-doping has been predicted to establish a wide-bandgap topological insulator phase. Here, we report on a mechanism that allows for epitaxial deposition of high-quality crystalline BBO thin films on SrTiO3 substrates despite a significant lattice mismatch of as large as 12%. It is revealed that the growth takes place through domain matching epitaxy, resulting in domains with alternating lateral sizes of 8 and 9 BBO unit cells. In particular, a structurally modified interface layer is identified which serves as a nucleation layer for the BBO films and gradually relieves the strain by decoupling the film lattice from the substrate. The BBO growth mechanism identified here may be prototypical for prospective thin film deposition of other perovskites with large lattice constants.The perovskite BaBiO3 (BBO) is a versatile oxide parent material which displays superconductivity upon p-doping, while n-doping has been predicted to establish a wide-bandgap topological insulator phase. Here, we report on a mechanism that allows for epitaxial deposition of high-quality crystalline BBO thin films on SrTiO3 substrates despite a significant lattice mismatch of as large as 12%. It is revealed that the growth takes place through domain matching epitaxy, resulting in domains with alternating lateral sizes of 8 and 9 BBO unit cells. In particular, a structurally modified interface layer is identified which serves as a nucleation layer for the BBO films and gradually relieves the strain by decoupling the film lattice from the substrate. The BBO growth mechanism identified here may be prototypical for prospective thin film deposition of other perovskites with large lattice constants.