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4시 20분부터 제1과학관 31214 e+강의실에서 다과를 준비하오니 많은 참석 부탁드립니다
제목: Electron phonon coupling effect in 4d transition metal oxide magnetism
연사: 김 창 영 교수님 (연세대학교)
일시: 2011년 6월 1(수) 오후4:30
장소: e+첨단강의실 (31214호실)
Spin triplet superconductivity observed in Sr2RuO4 triggered the research on 4d transition metal oxides. The triplet pairing for the superconductivity in Sr2RuO4 is theoretically suggested that the pairing is mediated by the exchange of ferromagnetic (FM) fluctuation. However, absence of ferromagnetic fluctuation and repeated observations of incommensurate antiferromagnetic (AFM) fluctuation from inelastic neutron scattering indicate that a better understanding of magnetism is needed.
Related to the issue in Sr2RuO4 is the magnetism in Ca2-xSrxRuO4 (CSRO) for which RuO6 octahedra are rotated. While density functional calculations predict FM ground state for systems with rotated RuO6, AFM ordering has recently been observed in the magnetic susceptibility data from CSRO. As the theoretically predicted FM ground state of RuO6 system is known to be closely related to the pairing mechanism of Sr2RuO4 spin-triplet superconductivity, AFM ordering observed in CSRO raises questions about the FM fluctuation mediated spin triplet superconductivity in Sr2RuO4.
For a better understanding of the magnetic phase diagram, we performed high-resolution angle resolved photoemission on Sr2RuO4 as well as on a related material Sr2-xLaxRhO4. ARPES results from systems with rotated RuO6 octahedral (surface states of Sr2RuO4 and Sr2-xLaxRhO4) show strong kink features in the band dispersion. The kink structure causes enhanced van Hov singularity and increases the density of states at the Fermi level, which in turn affects the magnetism. The origin of kink is found to be from the electrn phonon coupling. By comparing the magnetic properties and electronic structures of CSRO, SLRhO and SLRuO, I will try to explain the role of electron-phonon coupling in the magnetism of 4d transition metal oxides.
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