Condensed Matter

The research activities in the field Condensed Matter Physics and Materials Science cover the areas:

• Soft Matter, Polymers and Liquids
• Semiconductor Physics, Physics of Low-Dimensional Systems, Surfaces and Interfaces
• Magnetic Materials, Superconductivity and Ionic Conductors
  

Each topic ranges over a great variety of disciplines, summarized below, and span from fundamental to applied physics.

Soft Matter, Polymers and Liquids

Subject Cataloge

Basic Physics:

Amorphous Condensed Matter,
Glass-Forming Liquids,
Molecular Liquids,
Polymer and Polymer Surfaces,
Nucleation Phenomena,
Pattern Formation,
Self-Organized Criticality,
Structure and Dynamics of
Complex Materials

Theory of liquids

Review:

When cooling down a liquid it generally undergoes an abrupt transition at the melting point into a highly ordered crystalline phase. Soft condensed matter, to the contrary, presents cases where this does not happen in a straight forward manner. Cooling down silica, perhaps mixed with alkali oxides the liquid is easily undercooled below it’s melting point and solidifies into a glass, i.e. a disordered structure similar to that of the liquid. Similar scenario happen with many organic and anorganic substances, a well-known example is glycerol. But even if a liquid transforms, disorder of structure or of orientational degrees of freedom may prevail. Some organic liquids transform in a so-called liquid-crystalline phase where a certain degree of orientational order of the molecules is achieved, however their site distribution is still as random as in the liquid. Liquid-crystalline displays are a well-known application of this effect. But also the opposite may happen in the so-called plastic-crystalline phase where the ordered structure of the molecules is accomplished by different degrees of orientational disorder of the molecules.

Suspensions or emulsions are also liquids, and despite of the complex chemistry of its constituents they are in many aspects representative for very simple interactions in a liquid, however on a different length and time scale.

In general polymers have a complex microscopic architecture and consist of long molecular chains with disperse lengths. Both facts prevent crystallization when cooled down from the melt and in fact most polymers solidify in disorder or with only small fractions of partial crystalline order.

In the Physics Department soft condensed matter, polymers and liquids are studied theoretically and experimentally. From a more fundamental point of view one aims to find the basic physical principles of this huge area of condensed matter physics. From a more practical view one tries to explain the functional behavior from its microscopic basis. To do so it is important to study structure, dynamical and electronic properties on the level of the molecules or atoms and at times ranging from as short as femto-seconds to every day times scales of hours or more.

Theoreticians from the Physics Department have elaborated a consistent picture of the dynamical properties of viscous liquids and of the liquid-to-glass transition – so called mode-coupling theory of viscous liquids. The solidification of a viscous liquid to a stiff glass happens via a critical slowing down of internal movements. Experimentalists at the Department and other places verified this scenario by numerous experiments with elastic and inelastic scattering of neutrons, synchrotron radiation, visible light and computer simulation studies. It is part of the beauty of the nature that viscous liquids as different as suspensions, polymer melts, silica melts or protein solutions follow this general description.

Of course each material exhibits also its specific behavior. At the Physics Department spectroscopic methods and atomic force microscopy are used to deal with these questions. Short time spectroscopy, that means the observation of electronic and vibrational excitations in the 10-14 to -12 second region gives access to the electronic basis of the essential physico-chemical processes in soft matter. The photophysical generation of trapped electrons is of special importance in chemical and biological reactions and water is certainly the most fundamental system to study these phenomena. For example short time laser spectroscopy at the Physics Department could establish details of the 3-dimensional movement of solvated electrons in a cage formed by the neighboring H2O molecules. Different aspects are revealed by other spectroscopic techniques, e.g. optical hole burning. This methods allows to mark individual molecules, for example chromophors and then to determine their localized or long-range motion.

It remains the question what all these microscopic aspects have to do with the functional properties of soft matter materials, important for applications. The following list of examples may elucidate this: The actual thermal history of a glass, i.e. the particular way of freezing the internal motion determines the mechanical and thermal properties of a glass. Adding only a few % of water to volcanic melt changes its viscosity by orders of magnitude. The fraction of disordered-to-ordered structure in a polymer determines decisively its mechanical properties. To understand photolysis the motion and excitation of electrons in the femto-second region must be known. For fuel cells which eventually work with methane instead of pure hydrogen catalysis and transportation at the polymer electrolyte has to be understood, the extremely thin polymer coating of CDs or magnetic memories depend on the wetting/dewetting properties of these polymers.

Semiconductor Physics, Physics of Low-Dimensional Systems, Surfaces and Interfaces

Subject Cataloge

Basic Physics:

Self assembled InAs quantum dot on GaAs

IR-quantum cascade lasers (QCL) formed by Si/SiOx multilayers

Applied Physics:

Surface Reactions and Catalysis,
Chemical, Biological and
Multifunctional Sensors,
Electronic and Optoelectronic
Devices,
Laser Development,
Thin Film Solar Cells,
Nanostructure Technology,
Energy Conversion,
Fuel Cells

Nano-electronic device contact structure

Review:

In the first half of the 20th century the physical properties of three-dimensional crystals was the main focus of interest for solid-state physics. However, since the invention of the transistor in 1947 more and more emphasis has been placed on low dimensional solid-state systems, extremely thin layers, the interfaces between different solid-states, quantum wires and quantum dots because these systems are of particular importance for a whole range of current and future applications. The Physics Department of the Technische Universität München plays a leading role in international research activities taking place in this crucial area of modern physics. These research activities cover all sorts of different areas including the manufacture of new materials and material combinations using modern growth methods, the fundamental study of these material systems and suitable model systems using experiments and theories, the development of new research methods and theoretical approaches, and application related research in the fields of microelectronics, telecommunications, sensor technology and power engineering. In particular, interdisciplinary research has gained in importance leading to all kinds of productive forms of cooperation between researchers from the fields of biology, chemistry, information technology, mathematics and medicine. Researchers also cooperate with engineering scientists from the fields of electrical engineering and mechanical engineering. The interdisciplinary nature of the everyday work of scientists, as well as the close contact they maintain with all sorts of companies in the Munich area, contributes significantly to the unique character of the study of physics at the TU Munich: scientific depth coupled with innovation and concrete relevance to society.

Magnetic Materials, Superconductivity and Ionic Conductors

Subject Cataloge:

Basic Physics:

Chirality,
Critical Phenomena,
Giant Magneto-Resistance,
De Haas-van Alphen effect in
low dimensional systems,
High Temperature
Superconductivity (HTS),
Itinerant and Local Moments,
Magnetic Multilayers,
Magneto-Caloric Effects,
One-Dimensional Spin-Chains,
Metallic Nanostructures,
Polarized Neutrons,
Quantum Magnets,
Renormalization Group Theory,
Spin Dynamics and Spin Transport

Magnetic multilayer structure

Applied Physics:

Coated Conductors,
Cryotechnology,
Magnetoelectronics,
Magnetosensors,
Micromechnical Magnetometry,
Thermoelectrics,
Thin Film Technology

Metallic nano-wire