Macro economy comprises heterogeneous and interacting agents such as firms, banks, and consumers. How they are interconnected among themselves, namely economic networks, are crucial for understanding supply and demand shocks, price fluctuations (inflation and deflation), propagation of economic shocks due to exogeneous events including natural disasters and financial crises.

A large amount of data have been accumulated and available to such an extent to observe the economic networks in details at nationwide or worldwide scales. Complex network science and related studies have been helpful to investigate a variety of economic and social networks based on the detailed observation. Recent examples of such studies are shown in this manuscript.

We have studied nonlinear response and terahertz (～10¹² Hz) higher harmonic generation in thin films of Cd₃As₂ , a three-dimensional Dirac semimetal. Nonperturbative third harmonic generation was clearly observed at room temperature using a tabletop light source. Unprecedented efficiency for the terahertz frequency conversion was discussed with a microscopic picture considering the intraband acceleration of electrons near the Dirac node. The results pave the way toward novel devices for high-speed electronics and photonics based on topological semimetals.

The electron spin coherence time of the solid-state spin qubit is predicted to screen quantum materials. An algebraic representation of electron spin coherence in materials was obtained by the generalized scaling of spin coherence with the electron and nuclear spin characteristics. The materials with long spin coherence are obtained by using the expression, pointing to the oxides and chalcogenides as potential qubit materials.

We have been developing a non-destructive muonic X-ray analysis for extraterrestrial materials. Ten coarse Ryugu samples, which were allocated to the initial analysis STONE team, have been investigated at J-PARC MUSE. Significant muonic X-rays of C, N, O, Na, Mg, Si, S and Fe were detected from Ryugu and CI chondrite (Orgueil). These elemental ratios are in a good agreement with the reported values for CI chondrites, except for the 25% lower O/Si ratio for Ryugu relative to CI. This means that Ryugu is depleted of oxygen by 11.3% by mass compared to CI, assuming similar Si concentration for Ryugu to CI chondrites.