[原分所] 1/15(Tue.) IAMS Lecture Announcement- Prof. X.D. Cui 崔曉冬副教授
截止日期：2013-01-15
IAMS Lecture Announcement中研院原分所演講公告
Title: Optical signature of inversion symmetry and spin-valley coupling in atomically thin dichalcogenides.
Speaker: Prof. X.D. Cui 崔曉冬副教授 (Physics Department, University of Hong Kong, Hong Kong)
Time: 2:00-4:00PM, January 15 (Tuesday)
Place: CT Chang Memorial Hall, IAMS (本所張昭鼎紀念講堂 臺大校園內)
Contact: Dr. Lain-Jong Li 李連忠博士
Abstract:
Motivated by the triumph and limitation of graphene for electronic applications, atomically thin layers of group VI transition metal dichalcogenides are attracting extensive interest as a class of graphene-like semiconductors with a desired band-gap in the visible frequency range. The monolayers feature a valence band spin splitting with opposite sign in the two valleys located at corners of 1st Brillouin zone. This spin-valley coupling, particularly pronounced in tungsten dichalcogenides, can benefit potential spintronics and valleytronics with the important consequences of spin-valley interplay and the suppression of spin and valley relaxations. Here we report the first optical studies of WS2 and WSe2 monolayers and multilayers. The efficiency of second harmonic generation (SHG) shows a dramatic even-odd oscillation consistent with the presence (absence) of inversion symmetry in even (odd) layer. Photoluminescence (PL) measurements show the crossover from an indirect band gap semiconductor at mutilayers to a direct-gap one at monolayers. The PL spectra and first-principle calculations consistently reveal a spin-valley coupling of 0.4 eV which suppresses interlayer hopping and manifests as a thickness independent splitting pattern at valence band edge near K points. This giant spin-valley coupling, together with the valley dependent physical properties, may lead to rich possibilities for manipulating spin and valley degrees of freedom in these atomically thin 2D materials.
Title: Optical signature of inversion symmetry and spin-valley coupling in atomically thin dichalcogenides.
Speaker: Prof. X.D. Cui 崔曉冬副教授 (Physics Department, University of Hong Kong, Hong Kong)
Time: 2:00-4:00PM, January 15 (Tuesday)
Place: CT Chang Memorial Hall, IAMS (本所張昭鼎紀念講堂 臺大校園內)
Contact: Dr. Lain-Jong Li 李連忠博士
Abstract:
Motivated by the triumph and limitation of graphene for electronic applications, atomically thin layers of group VI transition metal dichalcogenides are attracting extensive interest as a class of graphene-like semiconductors with a desired band-gap in the visible frequency range. The monolayers feature a valence band spin splitting with opposite sign in the two valleys located at corners of 1st Brillouin zone. This spin-valley coupling, particularly pronounced in tungsten dichalcogenides, can benefit potential spintronics and valleytronics with the important consequences of spin-valley interplay and the suppression of spin and valley relaxations. Here we report the first optical studies of WS2 and WSe2 monolayers and multilayers. The efficiency of second harmonic generation (SHG) shows a dramatic even-odd oscillation consistent with the presence (absence) of inversion symmetry in even (odd) layer. Photoluminescence (PL) measurements show the crossover from an indirect band gap semiconductor at mutilayers to a direct-gap one at monolayers. The PL spectra and first-principle calculations consistently reveal a spin-valley coupling of 0.4 eV which suppresses interlayer hopping and manifests as a thickness independent splitting pattern at valence band edge near K points. This giant spin-valley coupling, together with the valley dependent physical properties, may lead to rich possibilities for manipulating spin and valley degrees of freedom in these atomically thin 2D materials.