Condensed Matter Seminar Series

The Mesoscopic X-ray Edge Problem

Dr. Martina Hentschel

Dept. of Physics, Duke University
Dept. of Physics, University of Regensburg (after April, 2004)

Thursday February 26, 11:00 am, Room 234, Physics Building

Abstract: We study many-body effects associated with a sudden perturbation in a mesoscopic system, finding substantial differences from the bulk case. One example is the sudden, localized perturbation caused by an x-ray exciting a core electron into the conduction band. Here, Anderson orthogonality catastrophe (AOC) competes with a many-body effect caused by the interaction of the conduction electrons with the core hole. In the bulk, this produces deviations from the naively expected photoabsorption cross section in the form of a peaked or rounded edge.  For a coherent system with chaotic dynamics, such as a nanoparticle or quantum dot, we use a random matrix model and find substantial changes: (1) the finite number of particles leads to an incomplete AOC, (2) the sample-to-sample fluctuations of the discrete energy levels produce a distribution of AOC overlaps, and (3) most importantly, the dipole matrix elements connecting the core and conduction electrons are substantially modified. One of our key results is that a photoabsorption cross section showing a rounded edge in the bulk will change to a slightly peaked edge on average as the system size is reduced to a mesoscopic (coherent) scale.

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