Berlin 2012 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 49: Ultrafast Phenomena
HL 49.6: Talk
Wednesday, March 28, 2012, 10:45–11:00, EW 202
Femtosecond thermomodulation in Cu — •Johanna Flock1, Markus Beyer1, Manuel Obergfell1, Christian Monachon2, Thomas Dekorsy1, and Jure Demsar1, 2, 3 — 1Dept. of Physics and CAP, Univ. of Konstanz, D-78457 — 2Laboratory for Mechanical Metallurgy, EPFL CH-1015 — 3Complex Matter Dept., Jozef Stefan Institute, SI-1000
Since discrepancies between the two temperature model[1] in the thermomodulation (TM) scenario[2] and experimental data exist[3], we have performed systematic measurements of the time-evolution of the dielectric function in Cu thin films over broad spectral range (1.5-2.5eV) as a function of photoexcitation energy (1.55eV and 3.1eV) and density. Here excitation with 1.55eV results in intraband transitions within the sp-band while in the case of 3.1eV interband processes from the narrow d-band 2eV below the Fermi level to the sp-band dominate. For both excitation energies the spectral changes are consistent with the fs-TM scenario. Only for the case of the intraband excitation the predicted excitation density dependence of the e-ph thermalization rate[1] is observed. For 3.1eV excitation energy the relaxation dynamics is excitation density independent. These results imply that the relaxation strongly depend on the initial electron distribution function, and point out that numerous recent studies on high-Tc superconductors[4] need to be revisited. [1]Kaganov, Sov.Phys.JETP4,(1957); Allen, PRL59,(1987). [2]Brorson, PRL64,(1990). [3]Kabanov, PRB78,(2008); Gadermaier, PRL105,(2010). [4]Brorson, Sol.Stat.Comm.74,(1990); Perfetti, PRL99,(2007);Mansart, PRB82,(2010).