Berlin 2018 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 52: Superconductivity: Fe-based Superconductors - FeSe and LiFeAs

TT 52.1: Talk

Wednesday, March 14, 2018, 09:30–09:45, HFT-FT 101

Interfacial phonons in the single unit cell of FeSe grown on SrTiO₃(001) — •Dominik Rau¹, Tobias Engelhardt², Jasmin Jandke², Fang Yang², Endre Barta², Wulf Wulfhekel², and Khalil Zakeri Lori¹ — ¹Heisenberg Spin-dynamics Group, Physikalisches Institut, Karlsruhe Institute of Technology, Germany — ²Physikalisches Institut, Karlsruhe Institute of Technology, Germany

Among all Fe-based superconductors a single unit cell of FeSe on SrTiO₃ exhibits the highest transition temperature T_c. Despite the intensive research, the physical origins of the observed high T_c and the role of the interfacial phonons in superconductivity are still highly under debate. Utilizing high-resolution electron energy-loss spectroscopy we probe the phonon spectrum in a unit cell of FeSe epitaxially grown on Nb-doped SrTiO₃(001). The Fuchs–Kliewer interfacial phonons are observed to appear at energies of 57 and 91.5 meV near the zone center. Both modes exhibit a weak dispersion while increasing the wave vector from Γ towards the zone boundary (X-point). The intrinsic linewidth of the higher energy phonon mode is about 11.5 meV at the Γ-point and remains nearly constant over a large fraction of the Brillouin zone. The nearly momentum-independent phonon lifetime excludes particularly strong electron–phonon coupling near the zone center. This observation indicates that other bosonic excitations, e.g. those of electronic origin, should play an important role in the formation of Cooper pairs and superconductivity in this system. This work has been supported by DFG through the Heisenberg Programme ZA 902/3-1 and DFG Grant Wu 349/12-1 and by the Alexander von Humboldt Foundation.