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- 주제어 : Valleytronics (검색결과 5 건)
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Ullah, Farman,Sim, Yumin,Le, Chinh Tam,Seong, Maeng-Je,Jang, Joon I.,Rhim, Sonny H.,Tran Khac, Bien Cuong,Chung, Koo-Hyun,Park, Kibog,Lee, Yangjin,Kim, Kwanpyo,Jeong, Hu Young,Kim, Yong Soo American Chemical Society 2017 ACS NANO Vol.11 No.9
<P>The covalently bonded in-plane heterostructure (HS) of monolayer transition-metal dichalcogenides (TMDCs) possesses huge potential for high-speed electronic devices in terms of valleytronics. In this study, high-quality monolayer MoSe2WSe2 lateral HSs are grown by pulsed-laser-deposition-assisted selenization method. The sharp interface of the lateral HS is verified by morphological and optical characterizations. Intriguingly, photoluminescence spectra acquired from the interface show rather clear signatures of pristine MoSe2 and WSe2 with no intermediate energy peak related to intralayer excitonic matter or formation of MoxW(1-x)Se2 alloys, thereby confirming the sharp interface. Furthermore, the discrete nature of laterally attached TMDC monolayers, each with doubly degenerated but nonequivalent energy valleys marked by (K-M, K'(M)) for MoSe2, and (K-w, K'(w)) for WSe2 in k space, allows simultaneous control of the four valleys within the excitation area without any crosstalk effect over the interface. As an example, K-M and K-w valleys or K'(M) and K'(w) valleys are simultaneously polarized by controlling the helicity of circularly polarized optical pumping, where the maximum degree of polarization is achieved at their respective band edges. The current work provides the growth mechanism of laterally sharp HSs and highlights their potential use in valleytronics.</P>
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Controlling spin-orbit coupling strength of bulk transition metal dichalcogenide semiconductors
이영훈,Eu Pilsun,임창영,차재훈,김성헌,Denlinger Jonathan D.,김영관 한국물리학회 2021 Current Applied Physics Vol.30 No.-
Transition metal dichalcogenide (TMD) semiconductors are attracting much attention in research regarding device physics based on their unique properties that can be utilized in spintronics and valleytronics. Although current studies concentrate on the monolayer form due to the explicitly broken inversion symmetry and the direct band gap, bulk materials also hold the capability of carrying spin and valley current. In this study, we report the methodology to continuously control the spin-orbit coupling (SOC) strength of bulk TMDs Mo1-xWxSe2 by changing the atomic ratio between Mo and W. The results show the size of band splitting at the K valley the measure of the coupling strength is linearly proportional to the atomic ratio of Mo and W. Our results thus demonstrate how to precisely tune the SOC coupling strength, and the collected information of which can serve as a reference for future applications of bulk TMDs.
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박정민(Jungmin Park),김갑진(Kab Jin Kim),김상훈(Sanghoon Kim),유정우(Jung-Woo Yoo) 한국자기학회 2021 韓國磁氣學會誌 Vol.31 No.6
Graphene is a two-dimensional material having the charge, spin and valley degree of freedom used for information transfer. For spintronics, graphene has emerged as a leading candidate for device applications due to high mobility and ultra-low spin orbit coupling. Also, graphene is an attractive 2D material for valleytronics because valley polarization can be induced by electrical or mechanical tuning. In this review, we focus on the spin and valley transport in graphene. The spin transport properties of graphene are usually studied with nonlocal spin valve devices because pure spin current can be injected into graphene and be detected as electrical voltage. The electrical generation of a spin current in graphene was tried using the spin Hall effect. The valley transport in graphene is also possible when the inversion symmetry of graphene is broken by applying gate voltage or using bi-layer graphene. From these transport properties in graphene, we briefly introduce the research trends of a spin relaxation mechanism, the spin Hall effect and the valley Hall effect in graphene for spintronics and valleytronics with their applications.
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Excitonic Valley Polarization and Coherence in Few-layer MoS2
김동학,신민주,임대영 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.5
We study the excitonic valley polarization and coherence in few-layer MoS2 by using circularandlinear-polarization-resolved photoluminescence. The valley polarization is largest in monolayerMoS2 and decreases with increasing number of layers or temperature. Contrary to the valleypolarization, the linear polarization is negligibly small in monolayer MoS2 and increases with increasingnumber of layers or temperature. The temperature-dependent valley depolarization canbe explained by the exciton center-of-mass momentum-dependent electron-hole exchange interaction. The valley decoherence in few-layer MoS2 is much faster than the valley depolarization at lowtemperature and is steady against increasing temperature or photoexcitation intensity, indicatingthat the decoherence process does not involve phonon or carrier-carrier scattering. The dominantvalley decoherence has a pure dephasing origin and cannot be explained by the valley-depolarizinge-h exchange interaction.
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Edge-Limited Valley-Preserved Transport in Quasi-1D Constriction of Bilayer Graphene
Lee, Hyunwoo,Park, Geon-Hyoung,Park, Jinho,Lee, Gil-Ho,Watanabe, Kenji,Taniguchi, Takashi,Lee, Hu-Jong American Chemical Society 2018 NANO LETTERS Vol.18 No.9
<P>We investigated the quantization of the conductance of quasi-one-dimensional (quasi-1D) constrictions in high-mobility bilayer graphene (BLG) with different geometrical aspect ratios. Ultrashort (a few tens of nanometers long) constrictions were fabricated by applying an under-cut etching technique. Conductance was quantized in steps of ∼4<I>e</I><SUP>2</SUP>/<I>h</I> (∼2<I>e</I><SUP>2</SUP>/<I>h</I>) in devices with aspect ratios smaller (larger) than 1. We argue that scattering at the edges of a quasi-1D BLG constriction limits the intervalley scattering length, which causes valley-preserved (valley-broken) quantum transport in devices with aspect ratios smaller (larger) than 1. The subband energy levels, analyzed in terms of the bias-voltage and temperature dependences of the quantized conductance, indicated that they corresponded well to the effective channel width of a physically defined conducting channel with a hard-wall confining potential. Our study in ultrashort high-mobility BLG nano constrictions with physically tailored edges clearly confirms that physical edges are the major source of intervalley scattering in graphene in the ballistic limit.</P> [FIG OMISSION]</BR>
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