Condensed-Matter Physics & Materials Science Seminar
"Scanning tunneling microscopy study of KxFe2-ySe2 grown by molecular beam epitaxy"
Presented by Wei Li, Tsinghua University, China
Thursday, November 10, 2011, 4:30 pm — Small Seminar Room, Bldg. 510
The newly discovered alkali-doped iron selenide superconductors not only reach a superconducting transition temperature as high as 32 K, but also exhibit unique characters that are absent in other iron-based superconductors, such as anti-ferromagnetically ordered insulating phases, extremely high Neel transition
temperatures, and the presence of Fe vacancies and ordering. These features have generated considerable excitements as well as confusions, regarding the delicate
interplay between Fe vacancies, magnetism and superconductivity. In this talk, I will focus on the molecular beam epitaxy (MBE) growth of high-quality KxFe2-ySe2 thin films and in situ low-temperature scanning tunneling microscope (STM) measurement of their atomic and electronic structures. We demonstrate that a KxFe2-ySe2 sample contains two distinct phases: an insulating phase with well-defined √5×√5 order of Fe vacancies, and a superconducting KFe2Se2 phase containing no Fe vacancies. An individual Fe vacancy can locally destroy superconductivity in a similar way as a magnetic impurity in conventional superconductors. The measurement of magnetic field dependence of the Fe-vacancy-induced bound states reveals a magnetically-related bipartite order in the tetragonal iron lattice. These findings
elucidate the existing controversies on this new superconductor and provide atomistic information on the interplay between magnetism and superconductivity in iron-based superconductors. We have also prepared KxFe2-ySe2 films with (001) orientation on SrTiO3(001). The superconducting phase of this sample has a Tc of 48 K with charge ordering and C4 to C2 symmetry breaking. Finally I will briefly introduce our recent works on FeTe and topological insulators.
Hosted by: Genda Gu
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