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아래와 같이 콜로퀴움을 개최하오니 많이 참석해 주시기 바랍니다. 4시 20분부터 2층 라운지세미나실에 다과를 준비하오니 많은 참석 부탁드립니다 아 래 제목: Fractional Hall Physics of Epitaxial Graphene: Scanning Tunneling Spectroscopy Study at 20 mK with High Magnetic Field 연사: 송 영 재 박사(National Institute of Standards and Technology ) 일시: 2010년 3월 26일(금) 오후4:30 장소: 물리학과 세미나실(31355호실) 초록: Graphene, two dimensional carbon system sharing the same mother form with C60 and carbon nanotubes, is an ideal two dimensional electron system (2DES) with one atomic thickness and has unique electronic properties unlike any other materials yet studied [1]. Completely new physics emerges when quantum interactions dominate as graphene’s relativistic electrons are put under the extreme conditions of low temperatures and high magnetic fields [2,3]. Here I introduce the first scanning tunnelling spectroscopy measurements for the electron density of states of graphene in fields up to 14 T and at temperatures below 20 mK [4] by an ultra low temperature scanning tunneling microscope [5] that I constructed recently in NIST. The Landau levels, peaks in the density of states in a magnetic field, split into a quartet of states as both spin and valley (pseudo-spin) degeneracies are lifted. The valley splitting is much larger than the spin splitting and both show evidence of strong quantum exchange interaction effects. At particular fields when N=1 landau level peak locates on the Fermi level, the spectroscopy shows evidence of a new series of fractional quantum Hall states such as filling factors of 11/2, 9/2 and 7/2 as well as enhanced spin/valley splitting by exchange coupling. The spatial mapping for graphene’s even-filling, polarized odd-filling and fractional-filling states will be addressed, which has been a key issue as a phase-driven problem in 2DES for last decades.
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