Condensed matter theory – University of Copenhagen

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X-Ray and Neutron Science > Research > Condensed matter theory

Condensed matter theory

Theory of advanced materials and superconductivity

A large class of materials and man-made structures exhibit novel and unexplained electromagnetic behavior. Often this is caused by a fascinating interplay between the electron’s charge, spin and orbital character.

This figure shows a magnet floating below a supercon-
ducting ring. The magnetic field lines from the magnet
get pinned by the superconductor which locks it in
place.

At present, the research activities of the condensed matter theory group are mainly centered on the study of topological insulators and high-Tc superconductors.

Topological insulators were discovered in 2008 and exhibit properties similar to quantum Hall systems except that the spin-orbit coupling of the electron takes the role of an external magnetic field.

High-Tc superconductors include cuprate materials and the recently discovered iron-based superconductors. In both classes of materials the origin of superconductivity remains a mystery and constitutes one of the greatest challenges and open unsolved problems of modern physics.

Guided by new experiments we study simplified interacting Hamiltonians which capture the main aspects of the problem and thereby learn about the nature of these materials. For the high-Tc materials a current central theme is the role of competing fluctuation order in the cuprates and the symmetry of the electron pairing in the Fe-based superconductors. Depending of the specific problem, the theoretical techniques typically include mean-field (Bogoliubov- de Gennes) theory, diagrammatic approaches, exact diagonalization, and numericalMonte Carlosimulations.  

The ultimate goal of our efforts is to acquire new fundamental understanding of advanced materials and be able to propose new systems with other novel properties and possibly higher Tc superconductivity.

Illustration of the copper (blue spheres) and oxygen (red spheres) ions forming two-dimensional sheets that constitute the most important parts of the crystal structure of high-temperature superconductors. Charge transport between these layers can occur through superconducting tunneling of Cooper pairs, illustrated here by the mobile yellow spheres.

For further information, contact Associate Professor  Brian Møller Andersen, bma@fys.ku.dk