NSRRC Activity Report 2022

Physics and Materials Science 013 In summary, Yang and his group has demonstrated a novel approach to the synthesis of twisted lateral homostructures with orientation and phase conjunction turnabilities. This is a significant leap ahead of the conventional concept of epitaxy. With a patterned prototype device, they further demonstrated that the proposed approach is not only compatible with conventional lithography and etching processes, but also could be universally applied for fabricating various twisted complex materials. The results demonstrate the excellent controllability and unbounded conjunction tunability of the lateral homostructures using this method, which was subsequently named “weave epitaxy”. Such an approach not only provides a new way to design twisted lateral homostructures but also depicts an entirely different conceptual scene for epitaxial growth. (Reported by Yu-Chen Liu, National Cheng Kung University) This report features the work of Jan-Chi Yang and his collaborators published in Nat. Commun. 13 , 2565 (2022). TPS 09A Temporally Coherent X-ray Diffraction TPS 45A Submicron Soft X-ray Spectroscopy TLS 13A1 X-ray Scattering TLS 17A1 X-ray Powder Diffraction TLS 17B1 X-ray Scattering • XRD, XAS • Materials Science, Condensed-matter Physics Reference 1. P. C. Wu, C. C. Wei, Q. Zhong, S. Z. Ho, Y. D. Liou, Y. C. Liu, C. C. Chiu, W. Y. Tzeng, K. E. Chang, Y. W. Chang, J. Zheng, C. F. Chang, C. M. Tu, T. M. Chen, C. W. Luo, R. Huang, C. G. Duan, Y. C. Chen, C. Y. Kuo, J. C. Yang, Nat. Commun. 13 , 2565 (2022). CaCu 3 Ru 4 O 12 : An Unusually High-Kondo-Temperature Transition-Metal Oxide Using a combination of bulk sensitive hard and soft X-ray electron spectroscopy, the authors confirm that CaCu 3 Ru 4 O 12 is a high Kondo temperature metallic oxide. T he Kondo effect involves the scattering of conduction- band electrons in a metal by localized magnetic impurities. It was originally observed as a minimum in electrical resistivity for a metal with magnetic impurities at low temperatures, along with coupled changes in the magnetic susceptibility and specific heat. Subsequently, the Kondo effect has been observed in many Ce, Yb, and U-based materials in which the localized magnetic 4f electrons hybridize with the conduction-band electrons and can lead to heavy fermion behavior. 1 However, the Kondo effect and heavy fermion behavior are rarely observed in oxides and LiV 2 O 4 is considered to be one such material. 2 More recently, the transition-metal oxide CaCu 3 Ru 4 O 12 (CCRO) has been considered as a Kondo material with heavy fermion behavior. 3 However, this hypothesis has been contested and debated in the literature. 4 In this highlight, through an international collaboration spanning Germany, Taiwan, Japan, Korea and Austria, researchers carried out a comprehensive study to determine whether CCRO can be best described as a high-Kondo-temperature transition-metal oxide. 5 The authors first carried out a careful comparison of the magnetic susceptibility of CCRO with that of CaCu 3 Ti 4 O 12 (CCTO). While the magnetic susceptibility of CCRO matched the data published in the literature, it exhibited an order of magnitude lower magnetic susceptibility compared with that of CCTO. This result implies that CCRO is nonmagnetic, in which case the Cu ions must be monovalent (with a non-magnetic 3d 10 configuration) or trivalent such as a nonmagnetic insulator NaCuO 2 . To confirm whether Cu ions in CCRO are magnetic, the authors carried out Cu L-edge X-ray absorption spectroscopy (XAS) and Cu 2p–3d resonant photoelectron spectroscopy (PES) at TPS 45A1 , the Submicron Soft X-ray Spectroscopy beamline at the NSRRC, as shown in Fig. 1 (see next page). The peak positions and line shape of the Cu L-edge XAS and the on-resonance 2p–3d PES spectra are typical of divalent Cu; hence, Cu in CCRO is not monovalent or trivalent.