Photon Science Seminar: New Dimensions of Angle resolved Photoemission from Solids; Attosecond physics without an attosecond laser

New Dimensions of Angle resolved Photoemission from Solids; Attosecond physics without an attosecond laser

Speaker:  Wolfgang Eberhardt, DESY

The determination of excited electron lifetimes in solids and on surfaces is of high current interest. Knowledge about these excited states is of great importance for the understanding and control of photophysical processes, ranging from charge generation in solar cells to photochemistry as for example photo-activated splitting of water. We here use conventional angle resolved photoelectron spectroscopy to determine these lifetimes (1,2). This experimental technique has been very successfully employed to determine the occupied band structure of solids (3) to the extent that the results are by now incorporated into basic solid state physics textbooks. Angle resolved photoemission also reveals the excited state lifetime as originally shown for Cu (4). This is based upon monitoring the intensity of well identified interband transitions as the energy of the photons is changed. As this requires some careful calibrations, this has not been widely used so far.

Apart from the lifetime measurements, these data also reveal the existence of very strong final state resonances located approximately 20 eV above EF. At these resonances, the transition intensity varies by an order of magnitude over a photon energy range of 1-2 eV. These final states are associated with bands derived from 4f- (5f-) atomic orbitals, as the demonstrated by the fact that the sp-like surface state does not couple to these final states.

As the interest in these lifetime measurements is growing, there are no obstacles to use this technique for other single crystalline materials. Moreover these measurements are complementary to the data obtained by direct as-laser techniques (5,6).