Inorganic oxides display a variety of useful properties e.g. as molecular sieves, catalysts and magnetic storage. Modifying inorganic materials by incorporating organic ligands is one to build novel materials retaining some properties of the parent structures. An important field of interest is the investigation of the magnetic behaviour of hybrid inorganic-organic framework compounds. Creating low-dimensional magnetic materials in a rational way by having control over the kind of connectivity offers is still a challenging subject in the field of molecular magnetism. The PhD student will focus on new transition metal phosphonates for which control over the dimensionality of the resulting transition metal(II) phosphonate compound is gained. The structural characterization will be followed by detailed investigations of the electronic and magnetic properties.

Prof. E. Rentschler (JGU Mainz)
www.ak-rentschler.chemie.uni-mainz.de  

Molecular clusters of 3d transition metals continue to be a main research area due to their fascinating physical properties and their complex structures. In particular, they often show high-spin ground states and easy-axis-type magnetic anisotropy, giving a significant energy barrier to reversal of the magnetization. Thus, at sufficiently low temperatures they behave as nanoscale single domain magnets (SMMs). Magnetic molecules have been proposed as a novel route to a spin-based implementation of quantum-information processing. Within this field, the assembly of pre-formed polymetallic clusters by covalent bonds in a step-by-step strategy has become a quite desirable goal for chemists. However, very few examples has been reported of discrete covalently attached 3d transition metal clusters and even in a less number of examples a rational strategy has been employed. The PhD student will focus on linking basic carboxylate cores of transition metals with appropriate bridging units through covalent bonds. The structural characterization of all compounds will be followed by detailed investigations of the electronic and magnetic properties.

Prof. E. Rentschler (JGU Mainz)
www.ak-rentschler.chemie.uni-mainz.de 

On quenching a binary mixture from high temperatures to below its demixing temperature it becomes unstable and undergoes the spontaneous non-equilibrium process of demixing. Starting from condensation nuclei, pure phase domains start to form and, subsequently, continuously grow in size. This fundamental phase ordering or coarsening process is quite well understood for the case of pure substances. For the much more realistic case of systems with impurities or quenched disorder, however, the understanding is much less complete. The randomness there leads to a pinning of domainwalls in favorable locations that substantially slows down the growth process. In this PhD project, the phenomenon of domain growth will be investigated mainly for the prototypic case of magnetic systems with random couplings or random fields using state-of-the art event-driven and generalized-ensemble Monte Carlo simulations. Possible extensions include applications to soft-matter systems.

Dr. M. Weigel (JGU Mainz)  

Adsorbed monolayers on surfaces exhibit a rich variety of interesting physicalphenomena. In particular, such layers often have rich phase diagrams in that they allow to form various ordered superstructures in addition to gaseous and fluid phases. The crucial factor determining this behavior is the question of commensurability or non-commensurability of the layer with the underlying substrate. Some of these ordering phenomena can be described by Potts models which are naturally two-dimensional due to the two-dimensional geometry of the adsorbed monolayer. For the case of a disordered substrate, this leads to the study of Potts models with disordering random fields. In this PhD project, a comprehensive analysis of the physics of monolayers adsorbed on a disordered substrate will be performed mainly through extensive numerical simulation studies of disordered Potts models.

Dr. M. Weigel (JGU Mainz)
Prof. Dr. K. Binder (JGU Mainz) 

Polymer brushes, i.e., polymers tethered with one end on a solid substrate, form an important class of functional materials with a wealth of applications. By the geometry of the substrate, one distinguishes polymer brushes with fibers crafted on a two-dimensional substrate and bottle brushes with chains tethered on a string. In this PhD project effects of quenched disorder on the physics of such systems are studied with numerical simulations, including chain-growth methods and Markov chain Monte Carlo simulations, and field-theoretic techniques. For the case of semiexible polymers disorder might occur in the stiffness along the chains. More generally, non-periodic grafting sites on the substrate induce effects of quenched disorder, which will be described with microscopic simulations as well as formulations of appropriate Ginzburg-Landau theories.

Dr. M. Weigel (JGU Mainz)
Prof. Dr. K. Binder (JGU Mainz) 

Liquid-solid interfaces play an important role in a number of phenomena encountered in biological, chemical and physical processes. Surface-induced changes of material properties are not only important for the solid support but also for the liquid itself. In particular it has been shown that water at the interface is substantially different from bulk water, even in proximity of apparently inert surface, such as a simple metal.The complex chemistry at solid-liquid interfaces is fundamental to heterogeneous catalysis and electrochemistry and has become especially topical in connection with the search for new materials for energy production. A quite remarkable example is the development of cheap yet efficient solar cells, whose basic components are dyes molecules grafted to the surface of an oxide material and in contact with an electrolytic solution. This PhD project propose the use of first principle molecular dynamics simulation to investigate the structural and spectroscopic properties of solid/liquid interface. First principle simulations permits to give a realistic description of interfaces where polarization effects (including electronic polarization) and finite temperature dynamics are naturally included. Collaboration with experimental groups working on vibrational spectroscopy of solid/liquid interface will permit to validate the computational approach and to verify theoretical predictions.

Jun.-Prof. Dr. M. Sulpizi (JGU Mainz)  

This PhD project focuses on the computational investigation of the microscopic mechanisms underlying energy conversion processes in bio-hybrid systems. The final aim is to predict the impact of the properties of the system on the reaction rates, which may guide the design of more efficient catalysts.Expanding and diversifying the sources of energy available to mankind arguably represents one of the most fundamental challenge now faced by society. Harvesting energy directly from the Sun and refining and concentrating the energy content of low-grade biomass are two of the most promising options for our future. The success of life and its ability to exploit nearly all forms of energy, including the lowest grade ones, is the motivation of bio-hybrid approaches to recover, concentrate, transform and store energy. Enzymes and bio-inspired synthetic catalysts can be merged with materials to develop cost-effective, renewable alternatives to the expensive noble-metal catalysts (e.g., platinum) that are currently used in artificial devices. However scaling up the processes for a commercial exploitation requires the engineering of interfaces which are both catalytically efficient and stable. A microscopic view of the chemical reactions taking place in those systems can be obtained by computer simulations, which complement the experimental observation and help to interpret it. This work aims to (i) identify the detailed steps in the energy staircase followed by the electrons from the catalytic centre to the electrode/ conducting material; (ii) quantify how fast they can move across the molecular bridges and conducting supports. The novelty stems from the application of my original modelling approach, based on first principles description of the reactive centres AND their heterougeneous environment, to fundamental electrochemical processes. In particular we will consider bio-hybrids where a nature-inspired catalyst is combined with conducting materials based on carbon.

Jun.-Prof. Dr. M Sulpizi (JGU Mainz)  

Prof. Dr. N. Blümer (JGU Mainz)

Prof. Dr. N. Blümer (JGU Mainz)

Magnetization switching by spin-polarized current injection, rather than by using externalmagnetic fields has recently stirred much attention, since this novel effect has thepotential for fast, reliable and simple switching, which is of great interest for applicationsin sensors, logic, microwave sources and storage devices. Based on our recent results, new geometries and novel materials will be explored to improve the switchingproperties of the devices. We will employ a range of experimental techniques andnumerical simulations to predict the ideal conditions for the device operation.
Low temperature magneto-transport measurements (10mK to room temperatures withfields up to 14T) will be carried out and the magnetoresistance effects will be correlatedwith the spin structure, which is imaged using high resolution photoemission electronmicroscopy, electron holography and other techniques. Using nanosecond current pulsesand microwave excitations, domain walls can be displaced and the dynamics of the domainwall propagation can be measured using time-resolved magnetotransport and imagingtechniques.
It is intended that part of the PhD/Postdoc stay can be carried out abroad at the industrialpartner’s central research facilities and regular visits there are part of the project.

Prof. Dr. M. Kläui (JGU Mainz)

The recently discovered class of iron pnictide/ chalcogenide compounds features apresumably unconventional mechanism of superconductivity, which is associated to theneighboring magnetic order, a rather 2-dimensional Fermi surface and low carrier density.The superconducting order parameter is predicted to be of the extended s-wave type with asign reversal of the order parameter between the different sheets of the Fermi surface.
We investigate FeSe (and derived doped compounds), the structurally simplestrepresentative of this class of materials. Epitaxial thin films are used as sampleswith a defined geometry and well-ordered surface, as necessary or advantageous for theintended investigations. We aim at the direct investigation of the superconducting energygap and the mechanism of superconductivity (strong coupling features) by tunnelingspectroscopy on planar junctions. Additionally, by film depositionon substrates with grain boundaries in-plane Josephson junctions for the investigation ofthe order parameter symmetry can be realised.
The project includes the set-up of a sputter deposition chamber as part of an existing UHVMBE/ sputter/ analysis cluster. The technology of tunneling junction preparation is basedon our work on magnetic tunneling junctions.

Prof. Dr. M. Kläui (JGU Mainz)

For several Heusler compounds band structure calculations predict a spin polarization of100\% at the Fermi energy. The experimental verification of thisprediction remains challenging, though. In principle spin resolved photoemissionspectroscopy is the most powerful experimental method for the investigation of bandstructures. However, the obtained agreement with the theoretical predictions, concerningthe qualitative energy dependence of the spin polarization as well as its magnitude, isgenerally poor.
We pursue a novel approach by combining state of the art thin film UHV preparation of Heusler thin films with in-situ spin-polarized UV-photoemission spectroscopy(SRUPS). Our preliminary work already demonstrated the advantages of this method.
Besides the photoemission experiments, the project includes the optimization of a new typeof spin detector and the preparation Heusler thin films and multilayers.

Prof. Dr. M. Kläui (JGU Mainz)

The interplay between spin and heat transport has recently stirred much attention. Itwas shown that temperature gradients associated with heat currents can generate spincurrents in magnetic nanostructure. Furthermore, these thermal spin currents can alsobe used to manipulate magnetization and for instance engineer pinning of magnetic domainwalls.
Electrical detection is going to be used to determine thermally induced spin accumulation.The temperature gradients can be obtained by Joule heating as well as optical Laser heatingto locally generate strong differences in temperature. The detection of domain walldynamics will be carried out by magneto-optical Kerr effect as well as magnetoresistivemeasurements.
The project is developed jointly with the the University of Konstanz where theoreticalcalculations are carried out. During the PhD, the student will have the opportunity tocollaborate with partners from the Priority Program and regular meetings with the theorycolleagues are part of the project. 

Prof. Dr. M. Kläui (JGU Mainz)

Thin epitaxial films of magnetic shape memory materials will enable new types of actuatorsdue to the large possible strain accompanying the magnetically induced reorientation of themartensite variants. This can lead to strains of 10% which are huge against magnetostrictiveor piezoelectric materials and enables new actuator concepts. In the preceding project weacquired the know how to prepare free standing epitaxial films based on Ni2MnGa usingsputtering methods. We used single crystalline substrates and epitaxial buffer layers that canbe selectively removed. The crystalline orientation can be selected using suitable substratesand the martensite transition temperature can be tuned choosing the target composition. Fordemonstration of easy twin boundary movement it will be essential to have films of the 5Mmodulated tetragonal crystal structure. Our project is aimed to achieve this special crystalstructure in the free standing films and in parallel we will optimize further our sacrificial layertechnology. For actual actuator development we cooperate with partners within the priorityprogram specialized in this field.
A second essential part of our project is to investigate basic properties of these fascinatingmaterials using a wide range of characterization methods. Besides magnetization andtransport measurements we perform x-ray diffraction and x-ray absorption spectroscopy.Using a polarized beam at the synchrotron the latter allows measurement of element specificatomic moments and their respective spin and orbital contributions. Here we will focus on theanisotropy of the orbital contribution, since it is responsible for the macroscopic magneticanisotropy. 

Prof. Dr. M. Kläui (JGU Mainz)

In the Ab-Initio Dynamics of Condensed Matter Group we are aiming to develop novel computational methods to study complex many-body systems such as liquids, biomolecules in solution and solids from first-principles. We are currently particularly interested in liquid water as well as metallic hydrogen. Along those lines we do have a PhD student position to offer, which consists of both method development and application.
Potential candidates must have a Master degree in Chemistry, Physics, or related discipline and a strong interest in computer simulations as well as programming. Basic experiences with Linux, numerical methods of theoretical physics/chemistry, electronic structure methods and/or molecular dynamics are highly desirable, but specific knowledge of any of these areas is less critical than exceptional intellectual ability.
Consideration of candidates will begin immediately until the position is filled. Questions and applications in electronic form including a cover letter and contact informations of at least two academic references should be directed to .

Jun.-Prof. Dr. T. D. Kühne (JGU Mainz)