A tight-binding model for the excitonic band structure of a one-dimensional molecular chain: UV-Vis spectra, Zak phase and topological properties

Recently organic optics becomes a hot topic due to the rapid development of organic light-emitting diodes, organic solar cells, and organic photon detectors. The optical spectra of the molecular semiconductors are difficult to solve an model from first-principles because (i) the very large number of atoms in a unit cell and (ii) the accurate theoretical excited state is still under development. Here we present a tight-binding model of an exciton band structure in a molecular chain. We take into account the intra-molecule and charge-transfer excitation within a molecular dimer in a unit cell, then we apply the tight-binding model by including the coupling between two types of excitations. We not only found that our calculations can explain a body of UV-Vis optical spectra of transition-metal phthalocyanines, but also a one-dimensional excitonic topological band structure if we fine-tune the couplings in a dimerized molecular chain. We have found a large space to obtain the topological Zak phase in the parameter space, in which there is a simple linear relationship between the hopping integrals between cells and within cell.Comment: 5 pages, 5 figure

Globalization and Inequality: Evidence from Within China

In this paper, we provide a case study of the impact of globalization on income inequality using data across Chinese regions. The literature on cross-country studies has been criticized because differences in legal systems and other institutions across countries are difficult to control for, and the inequality data across countries may not be compatible. An in-depth case study of a particular country's experience can provide a useful complement to cross-country regressions. We construct a measure of urban-rural income ratio for 100 or so Chinese cities (urban areas and adjacent rural counties) over the period 1988-1993. The central finding is that cities that experience a greater degree of openness in trade also tend to demonstrate a greater decline in urban-rural income inequality. Thus, globalization has helped to reduce, rather than increase, the urban-rural income inequality. This pattern in the data suggests that inferences based solely on China's national aggregate figures (overall openness and overall inequality) can be misleading. The negative association between openness and inequality holds up when we apply a geography-based instrumental variable approach to correct for possible endogeneity of a region's trade openness.

Broadband negative refraction in stacked fishnet metamaterial

We demonstrate a scheme to utilize the stacked fishnet metamaterial for all-angle negative refraction and subwavelength imaging within a wide frequency range starting from zero frequency. The theoretical predictions are verified by the finite-difference-in-time-domain (FDTD) numerical simulations. The phenomena come from the negative evanescent coupling between the adjacent slab waveguides through the breathing air holes perforated on metal layers.Comment: 8 pages, 4 figure