0428同步年報-2021-全

016 ACTIVITY REPORT 2021 An important aspect of the data in Fig. 1 is that a kink feature is observed in the dispersion for all metallic systems. Such a kink feature is normally interpreted to arise from electron-phonon coupling, but the energy scale of the kink, especially for NiSe 2 , is too large to have a phonon origin. In addition, the kink moves toward the lower-energy side as the molar mass decreases (that is, as S content increases), which is opposite what is expected from the electron-phonon interaction. Magnons and plasmons can also be excluded as the origin of the kink. If the kink originates from electron - magnon interaction, the energy scale of the kink is expected to increase as the system approaches the Mott insulating phase (that is, as S content increases). In contrast, plasmons have a much larger energy scale (few eV or greater) than the kink energy in the data. Another notable aspect of the kink feature is that the kink becomes stronger as the system approaches the Mott insulating phase, alluding to its possible connection to the MIT. Previous theoretical studies predicted that a strongly renormalized coherent part is confined to a low-energy scale set by J H . This effect explains why the kinks are generally found at the low- energy scale in a Hund’s metal. This hallmark of J H survives even in the vicinity of MIT at which U is dominant. Their ARPES data in Fig. 2(h) provide direct spectroscopic information on how the kink induced by J H evolves as ratio U / W increases. The kink moves toward the lower-energy scale as the system approaches the Mott insulating phase. In summary, the research team directly observed an evolution of the coherence energy scale via a kink feature. The ARPES data presented here show how the kink from J H evolves as the correlation strength increases. From DFT+DMFT calculations, they have confirmed that this kink originates from J H and is related to the crossing temperature scale. The suppression of Kondo screening by J H implements the kink feature at the low-energy scale; the kink moves toward the lower-energy side as the correlation strength further increases with S doping. Their results clearly demonstrate that the evolution of a kink can be understood by the evolution of the characteristic energy scale. (Reported by Cheng-Maw Cheng) This report features the work of Changyoung Kim, Cheng-Maw Cheng and their collaborators published in Nat. Commun. 12 , 1208 (2021). TLS 21B1 Angle-resolved UPS • High-resolution ARPES • Materials Science, Condensed-matter Physics Fig. 1 : Se content-dependent QP dispersion. (a) Phase diagram of NiS 2−x Se x . (b–f) ARPES data along direction Γ-X. (g) Energy distribution curves (EDC) at the Fermi momentum (k F ) as represented by dashed-dotted lines in panels (b–f). (h) QP dispersions obtained on fitting momentum distribution curves. (i–k) Doping-dependent band dispersion, Fermi velocity v F and effective mass m*, respectively. The linear coefficient of the specific heat γ is also plotted for comparison. [Reproduced from Ref. 1]