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DTSTART;VALUE=DATE:20240229T161500
DTEND;VALUE=DATE:20240229T161500
UID:15129@agenda.unifr.ch
DESCRIPTION:This thesis presents an ellipsometric study of the infrared response of \nbulk samples [1] and thin films of K doped p-terphenyl. In both cases, \na similarly weak Drude-response has been observed that undergoes \nanomalous changes around 90 K which can be associated with an \nenhanced charge localization. It seems likely that this charge \nlocalization is caused by a structural transition due to a twisting of \nthe p-terphenyl molecules which reduces the hopping probability \nof the doped electrons in the pi-orbitals. Such a structural transition \nof the molecules occurs in the pristine p-terphenyl around 195 K. The \nK doping is known to suppress this twisting, the corresponding \ntransition thus may well be reduced to about 90 K. \n\nNotably, an activation barrier due to such a twisting of the \nmolecules could also explain the energy gap feature that has been \nreported from an ARPES study [2] on the surface of p-terphenyl \ncrystals that have been covered with K ions.\n\nWhile the details of this charge localization remain to be fully \nunderstood, the presented infrared spectra certainly exclude the \npossibility that a bulk-like superconducting state develops in these \nK3 p-terphenyl samples. Further studies with microscopic probes will \nbe needed to settle the question of whether the charge localization \nmight be accompanied by the formation of a high temperature \nsuperconducting phase in a small fraction of the sample volume.\n\n[1] He Q, Marsik P, Le Mardelé F, et al. Infrared ellipsometry study of \nthe charge dynamics in K 3 p-terpheny. Physical Review B, 2023, \n107(9): 094520.\n[2] H. Li, X. Zhou, S. Parham, T. Nummy, J. Griffith, K. N. Gordon, E. L. \nChronister, and D. S. Dessau, Spectroscopic evidence of low-energy \ngaps persisting up to 120 K in surface-doped p-terphenyl crystals, \nPhys. Rev. B 100, 64511 (2019)
SUMMARY:Infrared ellipsometry study of charge dynamics in K-doped pterphenyl 
CATEGORIES:Soutenance de mémoire/thèse
LOCATION:PER 08\, 2.73\, Chemin du Musée 3\, 1700 Fribourg
URL;VALUE=URI:https://agenda.unifr.ch/e/fr/15129
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