A Lab-scale Spin and Angular Resolved Photoemission Spectroscopy Capability for 2D Valleytronics
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A Lab-scale Spin and Angular Resolved Photoemission Spectroscopy Capability for 2D Valleytronics Fabio Bussolotti, Zheng Zhang, Hiroyo Kawai, and Kuan Eng Johnson Goh* Institute for Material Research and Engineering (IMRE), #08-03, Innovis, 2 Fusionopolis Way, Singapore 138634 * [email protected] ABSTRACT We report on the establishment of a new lab-scale experimental capability for Spin and Angular Resolved Photoemission Spectroscopy (SARPES) for the study of valleytronics related materials. The ARPES capabilities of the system were demonstrated by measurement on gold [Au(111)] and molybdenum disulphide (MoS2) single crystals and the full functionality of the spin detector was also verified. Experimental results are compared with theoretical modeling by ab-initio band structure calculations. We discuss the potential scope of measurement that this experimental setup affords for investigating spin-related properties (e.g. spin-orbit coupling, valley transport, etc.) in layered materials. INTRODUCTION Transition-metal dichalcogenides (TMDCs; MX2 where M = Mo or W and X = S, Se, or Te, [see Figure 1(a)] are layered semiconducting materials with promising applications in emerging spintronic and valleytronics technology [1]. In the monolayer limit, TMDCs have a split valence band that is nearly fully spin polarized [2] near the K and -K points of the hexagonal Surface Brillouin Zone (SBZ) [Figure 1(b)]. The spin polarization is reversed between the K and -K points, implying the existence of a spin-valley coupling in the TMDCs. A detailed understanding of the electronic and spin properties on TMDCs is therefore required in order to truly harness the technological potentiality of these new class of materials. In this context, Angular Resolved Photoemission Spectroscopy (ARPES) represents as a powerful experimental technique for the direct determination of the electronic band structure of single crystalline materials, i.e. the dependence of the electron energy (E) on the electron momentum (k) [3]. Spinresolved ARPES (SARPES) represents a further advancement in the field allowing a complete characterization of electron states in a solid. In particular, it would serve as an effective tool for investigating a new class of exotic quantum properties related to the spin state of electrons such as those relevant in valleytronics related materials.
Figure 1. (a) Schematic of TMDCs (MX2) layered structure. (b) Spin splitting at valley K (-K) point of the SBZ of MX2 monolayer. Up and down spin polarizations are indicated by arrows.
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In this short communication, we report on the installation and testing of a new lab-scale experimental facility for Spin and Angular Resolved Photoemission Spectroscopy (SARPES) for the study of valleytronics 2D materials at the Institute of Materials Research and Engineerin
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