PhD project: Interface coupling in ferroelectric/ferromagnetic/superconductor systems

PhD project: Interface coupling in ferroelectric/ferromagnetic/superconductor systems

KU Leuven is an autonomous university. It was founded in 1425. It was born of and has grown within the Catholic tradition.

Quantum Solid-state Physics (QSP) is a research unit of the Department of Physics and Astronomy, one of the five departments of the Faculty of Science of KU Leuven.
We specialise in experimental research of functional electronic properties of solid-state systems. We focus in particular on quantum phenomena at the atomic and macroscopic scale, i.e., on the origin and tunability of functional electronic properties (magnetic, superconducting, semiconducting, dielectric), in systems with reduced dimensionality, from single-atom defects to nanoscale clusters, 2-dimensional materials, thin films, and 3-dimensional heterostructures. Our research is fundamental in nature and, when relevant, applications in functional systems and devices are also explored.
Eight faculty members lead an integrated community of more than fifty doctoral students, post-doctoral researchers and visiting professors. Our research is supported by a dedicated team of instrument specialists, technicians and administrative staff. We operate a wide range of in-house facilities dedicated to thin film growth (of magnetic, superconductor, semiconductor materials) with extensive in-situ characterisation capabilities, ion implantation and ion beam analysis, atomic cluster production and spectroscopy, nanolithographic patterning and device fabrication, scanning-probe microscopy and spectroscopy, low-temperature transport and magnetization measurements. A significant part of our research is also carried out using complementary techniques at international large-scale facilities, such as the ISOLDE facility at CERN, synchrotron facilities, free-electron lasers and neutron sources.

In this PhD project we will study how a ferroelectric (FE) layer exerts an influence on a ferromagnetic (FM) layer, which in turn is interfaced with a superconducting (SC) layer, ultimately leading to electric control of the superconducting layer. The main goal of this approach is that the ferromagnetic configuration can be altered by an electric field rather than a magnetic field, which requires much less electric power and which is much more adapted for miniaturization. However, the physical properties, magnetic configuration, chemical composition and roughness at the interfaces of such FE/FM/SC heterostructures are still largely unknown and require systematic investigations.

The main research questions to be addressed are therefore the following:

• What is the magnetic depth profile within the FE/FM/SC heterostructure?
• Can we tune the superconducting critical parameters of the SC layer by manipulating the magnetization direction in the FM layer via its coupling to a FE layer?

More specifically, we will synthesize a Si/FE/FM1/SC/FM2 heterostrucure. a first approach we will use BaTiO3 as FE, Fe as FM1 material, Co40Fe60 as FM2, and NbN as SC. The samples will be grown using the molecular beam epitaxy facilities in the KU Leuven Ion and Molecular Beam Laboratory (IMBL) facilities. Since the effects of interest are strongly dependent on the quality of the interfaces, special attention will be devoted to an in-depth study of their structural quality, including interface roughness and interdiffusion, precise layer thickness and local magnetization value. We will make use of X-ray scattering, scanning probe microscopy, Atom Probe Tomography, and Rutherford Backscattering techniques for the structural characterization. For the magnetic characterization we will mainly rely on magnetization measurements in our SQUID magnetometer and magnetotransport measurements at cryogenic temperatures to investigate the manipulation of the superconducting spin valve effect via the application of an electric field leading to a magnetoelectric coupling effect with the free layer in the stack. Since this will lead to an intricate magnetic structure near the interfaces, we will also make use of polarized neutron reflectivity and nuclear resonant scattering to study the magnetic depth profile in the layer stacks. We have extensive experience with both techniques (which will be performed at international large-scale international research facilities (such as ESRF in Grenoble, DESY in Hamburg and APS in Argonne), which will complement our in-house research.

This PhD research project is carried out within the framework of a broader and long-lasting close collaboration with imec Leuven (Imec R&D, nano electronics and digital technologies).

Profile

• You are a motivated researcher with a Master in physics, chemistry, nanotechnology, or related fields, with a strong background in (experimental) solid state physics.
• You obtained excellent results in your prior studies and are fluent in both spoken and written English.