Professor Allen directs his research broadly at the electronic structure of solids, and the relationship between electronic structure and low energy, low temperature properties. He is particularly interested in systems that are dominated by many-body effects and therefore cannot be well treated by conventional band theory. Typically these are systems with transition metal, rare earth or actinide elements, or low dimensional systems, which display behaviors involving heavy fermions, mixed valence fluctuations, the Kondo effect, Mott-Hubbard insulation, high temperature superconductivity, quantum critical fluctuations or other sources of non-Fermi liquid physics such as the electron fractionalization of the Luttinger liquid.
The experimental tool is laboratory or synchrotron-radiation-excited x-ray and electron spectroscopies, used to measure the spectral weights of single-particle or two-particle Green’s functions. These measurements can then be compared with spectral weight calculations from band theory or from model many-body Hamiltonians, and can be related to low energy properties by suitable theories. Off campus work is currently conducted at the Wisconsin Synchrotron Radiation Laboratory, the Advanced Light Source of the Lawrence Berkeley National Laboratory, and the SPring-8 Synchrotron in Japan.
Professor Allen is a Fellow of the American Physical Society (APS) and received the 2002 Frank Isakson Prize from the APS.