Wölfle Group

Magnetic phase diagram of the two-dimensional Hubbard model on the square lattice

We aim at a theoretical description of collective properties of electrons in quantum matter. In the focus of our interest are quantum phase transitions, ordered quantum states and quantum transport phenomena. Our goal is to develop new methods to solve the quantum many body problem, to identify new physical concepts for the interpretation of experimental observations of current interest and to calculate observable properties.

At present the following projects are in progress:

  1. Theory of critical behaviour near a quantum phase transition in metallic heavy-fermion compounds (e.g. YbRh2Si2). Explanation of the observed critical behaviour, e.g. of the specific heat, at the thermal phase transition near the quantum critical point.
  2. Theory of electron transport in lightly doped semiconductors of very small carrier density , like SrTiO3 doped with Nb or O2. Explanation of the observed T2 temperature dependence of the resistivity at low temperatures. Theory of the observed superconducting state of this extreme low density system taking into account the repulsive Coulomb interaction.
  3. Theory of strongly correlated electron systems like the Hubbard model or the periodic Anderson model in the framework of the spinrotation invariant slave boson theory of Kotliar and Ruckenstein. Derivation of the fluctuation contributions about the mean field solutions. Determination of the ordered states in the phase diagram and the instabilities w.r.t. phase separation and incommensurate order. Calculation of the spin and charge susceptibilities and of transport properties in the normal and superconducting state.

Prof. Dr. Peter Wölfle