Thin Films and Interfaces Group

Head of the group: Dr. Rudolf Schneider

Our group is specialized in the preparation and characterization of thin epitaxial films with superconducting or magnetic properties. The goals reach from basic investigations on the physics of thin films across the solution of technological problems such as patterning, contacting and passivation techniques to the realization of practically applicable components in the area of hf engineering and microelectronics. For the film preparation, facilities for sputtering and laser ablation are available. The patterning is performed in a cleanroom using UV-photolithography and ion-beam milling. The extended experimental equipment for characterization and analysis of the structural and magnetic properties as well as of the electrical, dielectrical, and ferroelectrical properties in low and high frequency ranges allows independent comprehensive investigations.

• Preparation of Epitaxial Oxides with Magnetic Properties
• Preparation of Superconducting Boride Films for Tunnel Diodes and Investigations in High-Frequency Fields

Preparation of Epitaxial Oxides with Magnetic Properties:

The main focus of our present research are thin films of cobaltates, oxides of the form ABO₃ with perovskite structure (A: rare-earth metal, B: transition metal Co, O: oxygen). Hole doping of LaCoO₃ leads to a ferromagnetic behavior, in the case of La_0.7Sr_0.3CoO₃ up to a critical temperature T_C = 240 K. Cobaltates show like manganites a pronounced magnetoresistance which is of interest with respect to applications. A combination with corresponding electron-doped cobaltates, presently under preparation and investigation in our group, can possibly enable the realization of magnetic pn-contacts which could be a key component for spintronics.

Fig. 1. Preparation of oxide films by Pulsed Laser Deposition (PLD)

Preparation of Superconducting Boride Films for Tunnel Diodes and Investigations in High-Frequency Fields:

The two-band superconductor MgB₂, discovered in 2001, has an amazingly high critical temperature of 39 K. The preparation of thin films of this material is challenging due to the required high Mg vapor pressure. We solved the problem by means of a special Mg vaporizer which enables in combination with B sputtering the fabrication of high-quality thin films with critical temperature of up to 37 K. We prepared from these films tunnel diodes using the natural oxide of MgB₂ as a tunneling barrier. The qualitity of these tunnel diodes was so outstanding that in conductivity measurements the phonon-induced structures could be detected. In collaboration with the theory group of IFP the most striking structure at an energy of 58 meV could be identified as signature of the interband pairing interaction, an exotic phenomenon which could be found up to now only in MgB₂ as best example for a two-band superconductor. We also investigated the microwave losses in constant external magnetic field measuring the surface impedance as a function of temperature and magnetic-field intensity for several frequencies between 5.7 and 18.5 GHz using a dielectric resonator technique. The results fulfilled the expectations for MgB₂ as a conventional but highly unusual type-II superconductor.

Fig. 2. High-frequency measurement system

Current group members (in alphabetical order):

• Andre Beck
• Dr. Dirk Fuchs
• Ernst-Peter Knaetsch
• Dr. Rudolf Schneider
• Dipl.-Phys. Markus Wissinger
• Dr. Alexander Zaitsev

Former group members: