Bulk spin polarization of magnetite from spin-resolved hard x-ray photoelectron spectroscopy

There is broad consensus that magnetite (Fe₃O₄) is a promising material for spintronics applications due to its high degree of spin polarization at the Fermi level. However, previous attempts to measure the spin polarization by spin-resolved photoemission spectroscopy have been hampered by the use of low photon energies resulting in high surface sensitivity. In this study we determine the intrinsic---i.e., bulk---spin polarization of magnetite by spin-resolved photoelectron spectroscopy on (111)-oriented thin films, epitaxially grown on ZnO(0001), with hard X-rays, making it a truly bulk-sensitive probe. This becomes possible by using a novel, specially adapted momentum microscope, featuring time-of-flight energy recording and an imaging spin-filter. [...]

Phys. Rev. B 104, 045129 (2021)

Controlling the electronic interface properties of AlO_x/SrTiO₃ heterostructures

Depositing disordered Al on top of SrTiO₃ is a cheap and easy way to create a two-dimensional electron system in the SrTiO₃ surface layers. To facilitate future device applications, we passivate the heterostructure by a disordered LaAlO₃ capping layer to study the electronic properties by complementary x-ray photoemission spectroscopy and transport measurements on the very same samples. We also tune the electronic interface properties by adjusting the oxygen pressure during film growth. [...]

Phys. Rev. Mater. 5, 065003 (2021)

Hard x-ray photoemission spectroscopy of LaVO₃/SrTiO₃: Band alignment and electronic reconstruction

The authors study, as a promising candidate for photovoltaic applications, the Mott insulator LaVO₃, epitaxially grown as a thin film on SrTiO₃. They elucidate the electronic properties by electrical transport and photoemission measurements. The origin of the conducting interface is identified to be electronic reconstruction due to the polar discontinuity between film and substrate. The authors find a potential gradient in the film and a downward band bending in the substrate, with the electrons residing in interfacial Ti states. [...]

Phys. Rev. B 103, 235128 (2021), Editors' Suggestion

Nanophysics at surfaces

The research activities of our group are concerned with the physics of low-dimensional systems, where the electron states resulting from dimensional confinement lead to unusual conduction properties and to phase transitions as a function of temperature.

Oxide interfaces

Our group focusses on the electronic structure of correlated systems in transition metal oxides (TMOs). Special interest lies in the interplay of different degrees of freedom (charge, spin, orbital, lattice) in the light of metal-insulator and other phase transitions.

Neutron and resonant X-ray spectroscopy

In our group we investigate complex, functional materials such as transition metal oxides, which are used in the emerging field of correlated nanoelectronics. Unlike with conventional semiconductors, exotic superconducting, orbital and magnetic states can be realized at the interfaces in layered structures comprising such materials.