0428同步年報-2021-全

110 ACTIVITY REPORT 2021 Current Status of TPS 39A NanoARPES Beamline T he investigation of emergent quantum materials provides a foundation to develop new technology. The novel phenomena from these materials including electrical, optical and magnetic properties provide opportunities for the development of quantum computing, energy storage, catalysis, etc . In the early stage of material discovery, the insight of electronic structure can give clues to shorten the period of development. To probe the band structure of novel materials, angle-resolved photoemission spectroscopy (ARPES) has emerged as a cardinal experimental tool to elucidate the emergence of many interesting physical properties in advanced materials, due to its unique capability to probe directly their momentum- resolved electronic structures. It allows researchers not only to map out the band dispersion and Fermi surface topology but also to understand comprehensively momentum- and energy-dependent complicated phenomena in advanced materials. A central challenge in condensed-matter physics is to investigate further the many-body systems in which strong interactions lead to novel ordered ground states. Examples include high- T c superconductors, complex oxides, graphene-based materials, 2D materials, transition-metal dichalcogenides, topological insulators, unconventional superconductors, heavy Fermion materials, Dirac semimetal and Weyl semimetals, etc . A plan of a novel nanoARPES beamline was approved in 2017. Two separate branches with different beam-focusing methods were planned to meet the research requests and to expand the scope of emergent quantum materials. A micro-focusing µARPES branch ( TPS 39A1 ) supported by Taiwan Consortium of Emergent Crystalline Materials and the NSRRC was constructed first; another construction plan of a nano-focusing ARPES beamline ( TPS 39A2 ) was also begun in 2019. The design of focusing optical systems at TPS 39A nanoARPES beamline was based on Kirkpatrick-Baez (K-B) mirrors and zone-plate techniques; a new endstation with a scanner stage aimed to enable a high-resolution ARPES at the micrometer and nanometer scale. The monochromator type is the active mirror-plane grating monochromator (AM-PGM), which was developed by the NSRRC. The novel AM-PGM design can deliver high energy resolution, high photon flux and a wider photon energy range. After the monochromator, the K-B mirrors focusing method was used at TPS 39A1 µARPES branch to achieve the design goal of a minimum spot size about 10 µm; the zone plate focusing method was used at TPS 39A2 nanoARPES branch to focus the beam spot size down to 100 nm. An elliptically polarized undulator (EPU) of period length 168 mm was used as a photon source. The operating photon energy is from 20 to 650 eV to cover most VUV and soft X-ray photon energy range. The insertion device of EPU168 was installed in November 2020. Owing to a pandemic of COVID-19, shipment of several beamline optics was delayed to the NSRRC, but most construction work was still on track. The beamline optics in a hutch before the monochromator were installed completely. The active mirror-plane grating monochromator is still under Fig. 1 : (a) Design of reshaped endstation TPS 39A1 µARPES. (b) Assembled endstation TPS 39A1 µARPES.