title: On Valence-Band Splitting in Layered MoS2.
abstract: As a representative two-dimensional semiconducting transition-metal dichalcogenide (TMD), the electronic structure in layered MoS2 is a collective result of quantum confinement, interlayer interaction, and crystal symmetry. A prominent energy splitting in the valence band gives rise to many intriguing electronic, optical, and magnetic phenomena. Despite numerous studies, an experimental determination of valence-band splitting in few-layer MoS2 is still lacking. Here, we show how the valence-band maximum (VBM) splits for one to five layers of MoS2. Interlayer coupling is found to contribute significantly to phonon energy but weakly to VBM splitting in bilayers, due to a small interlayer hopping energy for holes. Hence, spin-orbit coupling is still predominant in the splitting. A temperature-independent VBM splitting, known for single-layer MoS2, is, thus, observed for bilayers. However, a Bose-Einstein type of temperature dependence of VBM splitting prevails in three to five layers of MoS2. In such few-layer MoS2, interlayer coupling is enhanced with a reduced interlayer distance, but thermal expansion upon temperature increase tends to decouple adjacent layers and therefore decreases the splitting energy. Our findings that shed light on the distinctive behaviors about VBM splitting in layered MoS2 may apply to other hexagonal TMDs as well. They will also be helpful in extending our understanding of the TMD electronic structure for potential applications in electronics and optoelectronics.
authors.affiliation: State Key Laboratory of ASIC & System, School of Information Science and Technology, Fudan University , Shanghai 200433, China.|State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem & Information Technology, Chinese Academy of Sciences , Changning Road 865, Shanghai 200050, China.
authors.forename: Youwei
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of ASIC & System, School of Information Science and Technology, Fudan University , Shanghai 200433, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem & Information Technology, Chinese Academy of Sciences , Changning Road 865, Shanghai 200050, China.
authors.forename: Haomin
authors.initials: H
authors.lastname: Wang
authors.affiliation: State Key Laboratory of ASIC & System, School of Information Science and Technology, Fudan University , Shanghai 200433, China.
authors.forename: Ran
authors.initials: R
authors.lastname: Liu
authors.affiliation: Solid-State Electronics, The Ångström Laboratory, Uppsala University , Box 534, Uppsala SE-751 21, Sweden.
authors.forename: Shi-Li
authors.initials: SL
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of ASIC & System, School of Information Science and Technology, Fudan University , Shanghai 200433, China.
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Qiu
keywords: interlayer coupling; molybdenum disulfide; photoluminescence spectroscopy; spin−orbit coupling; valence-band splitting