Research & Facilities

Due to the constantly increasing available computational power and to the development of very efficient calculation algorithms, it is nowadays possible to predict very accurately material properties, basing simply on the fundamental principles of quantum mechanics. The newly established research group  "Ab initio theory of ferroelectric materials" focuses its research on complex material systems such as ferroelectric compounds or metallic nanowires on semiconducting substrates, which are modeled in the framework of the density functional theory. The calculations are performed in high performance computer clusters such as the HRLS in Stuttgart or the PC2 in Paderborn.

A ferroelectric is any piezoelectric which satisfies the following two conditions: (1) it possesses at least two stable polarization states in absence of external electric fields (2) the polarization states can be switched by means of an external electric field. Ferroelectrics show a multiplicity of unique and favorable physical properties and are therefore extensively used for applications such as electro-optical and acousto-optical devices. In particular, they are employed for the fabrication of the optical waveguides investigated in the SFB-TRR142. Bulk and surface properties of…

Low dimensional physics is characterized by a row of unusual effects, however many of them are not completely understood. 1D-electronic systems, as realized, e.g. in substrate supported nanowires, cannot be described by the Fermi liquid model. The Tomonaga-Luttinger model describes the electronic interactions in such conditions. Noble metal (Pt, Au) or rare earth silicide wires on semiconducting substrates (Si, Ge) are a marvelous playground for scientists dealing with the fundamental principles of 1D-physics. Unfortunately, our knowledge of the candidate systems is rather poor. In our group…

Surfaces and interfaces represent a discontinuity in the materials structure. They can be interpreted as 2D systems and might strongly differ from the corresponding 3D matter. Due to their exclusive properties, they are employed in many applications, e.g., as catalyst for chemical reactions, as a substrate for self-organizing molecular structures or for electron confinement. Many different examples of surface and interface configurations can be individuated. In our group we model the atomic structure of solid-solid, solid-liquid, solid-gas as well as solid-vacuum surfaces and interfaces.…

Incorporating a small amount of foreign atoms in a crystal is a procedure commonly referred to as crystal doping. The foreign atoms form structural defects in the host lattice, which together with intrinsic defects strongly influence the material properties. Both point defects (substitutionals, interstitial, vacancies) as well as extended defects (stacking faults, dislocations, grain boundaries) are a hot topic in basic and applied physics. Indeed, with an appropriate doping the electronic, magnetic, optic and mechanical properties of crystals can be tuned. Thereby theoretical models can be…