title: Direct Measurement of the Tunable Electronic Structure of Bilayer MoS2 by Interlayer Twist.
abstract: Using angle-resolved photoemission on micrometer-scale sample areas, we directly measure the interlayer twist angle-dependent electronic band structure of bilayer molybdenum-disulfide (MoS2). Our measurements, performed on arbitrarily stacked bilayer MoS2 flakes prepared by chemical vapor deposition, provide direct evidence for a downshift of the quasiparticle energy of the valence band at the Brillouin zone center (Γ̅ point) with the interlayer twist angle, up to a maximum of 120 meV at a twist angle of ∼40°. Our direct measurements of the valence band structure enable the extraction of the hole effective mass as a function of the interlayer twist angle. While our results at Γ̅ agree with recently published photoluminescence data, our measurements of the quasiparticle spectrum over the full 2D Brillouin zone reveal a richer and more complicated change in the electronic structure than previously theoretically predicted. The electronic structure measurements reported here, including the evolution of the effective mass with twist-angle, provide new insight into the physics of twisted transition-metal dichalcogenide bilayers and serve as a guide for the practical design of MoS2 optoelectronic and spin-/valley-tronic devices.
authors.affiliation: Department of Electrical Engineering, Columbia University , New York, New York 10027, United States.
authors.forename: Po-Chun
authors.initials: PC
authors.lastname: Yeh
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
authors.forename: Wencan
authors.initials: W
authors.lastname: Jin
authors.affiliation: Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
authors.forename: Nader
authors.initials: N
authors.lastname: Zaki
authors.affiliation: Department of Chemistry, Columbia University , New York, New York 10027, United States.|Theoretical Chemistry, TU Dresden , 01062 Dresden, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Kunstmann
authors.affiliation: Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Chenet
authors.affiliation: Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States.
authors.forename: Ghidewon
authors.initials: G
authors.lastname: Arefe
authors.affiliation: Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Jerzy T
authors.initials: JT
authors.lastname: Sadowski
authors.affiliation: Department of Electrical Engineering, Columbia University , New York, New York 10027, United States.
authors.forename: Jerry I
authors.initials: JI
authors.lastname: Dadap
authors.affiliation: Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.
authors.forename: Peter
authors.initials: P
authors.lastname: Sutter
authors.affiliation: Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States.
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.affiliation: Department of Electrical Engineering, Columbia University , New York, New York 10027, United States.|Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Osgood
keywords: MoS2; Stacked van der Waals structures; low energy electron microscopy (LEEM); photoemission; spectromicroscopy; twisted van der Waals materials