Research interests

A large variety of materials of experimental relevance are quantum systems in which both interactions and disorder play a dominant role. Their competition leads to very complex phases which pose one of the big challenges of modern condensed matter theory. Prominent examples are, e.g., highly doped semiconductors (or "electron glasses") driven close to the metal insulator transition, superconducting films, the closely related underdoped high temperature superconductors, or random quantum magnets and quantum spin glasses. In many cases their better understanding requires fundamentally new theoretical concepts that cannot be borrowed from approaches that apply to clean, crystalline matter. However, in contrast to a solid body of knowledge that has been accumulated on classical disordered systems, relatively little is known about these important complex and often glassy quantum systems, which are at the focus of my research.

Specifically, I am interested in a variety of disordered condensed matter systems:

Disordered electronic systems

• Universal glassy behaviour in a variety of electronic glasses: doped disordered semiconductors, semimetallic alloys, granular metals and 2D-metallic films.
• Aging and memory effects in electronic systems.
• Hopping conductivity
• Metal-insulator transition: Interplay of interactions and disorder
• Quantum glassiness and collective phenomena in electronic systems

Quantum glasses

• Quantum glass transitions (spin and electron glasses, Cooper pair glasses)
• Physical properties of the (quantum/classical) glass phase at low temperature
• Dynamical properties of coupled quantum two-level systems: collective modes, localization
• Interacting dipoles
• Many-body localization, an dit srelation to the glass transition

Superconductivitiy

• Dirty superconducting films
• Superconductor-insulator transition (disorder and field driven)
• Transport and collective behavior in Copper pair glasses
• High Tc superconductors
• Vortex liquid (Nernst effect)
• New phases in high magnetic fields

Systems in random external potential

• Vortex lattices, interfaces and other elastic systems in disordered media
• Depinning  
• Avalanches, glassiness and hysteresis in random field magnets (random field Ising model)
• Griffith phenomena
• Relation between Anderson (localization) transition and the random field transition

Heteropolymers

• Statistical mechanics of heteropolymers
• RNA and protein folding