Topological Semimetal-Insulator Quantum Phase Transition in Zintl Compounds Ba2X (X=Si, Ge)

By first-principles calculations, we find that Ba2X(X=Si, Ge) hosts a topological semimetal phase with one nodal ring in the kx=0 plane, which is protected by the glide mirror symmetry when spin-orbit coupling (SOC) is ignored. The corresponding drumheadlike surface flat band appears on the (100) surface in surface Green function calculation. Furthermore, a topological-semimetal-to-insulator transition (TSMIT) is found. The nodal line semimetal would evolve into topological insulator as SOC is turned on. The topologically protected metallic surface states emerge around the Gamma=0 point, which could be tuned into topologically-trivial insulator state by more than 3% hydrostatic strain. These results reveal a new category of materials showing quantum phase transition between topological semimetal and insulator, and tunability through elastic strain engineering.Comment: 14 pages. 4 figure

Signatures of strong correlation effects in RIXS on Cuprates

Recently, spin excitations in doped cuprates are measured using the resonant inelastic X-ray scattering (RIXS). The paramagnon dispersions show the large hardening effect in the electron-doped systems and seemingly doping-independence in the hole-doped systems, with the energy scales comparable to that of the antiferromagnetic magnons. This anomalous hardening effect was partially explained by using the strong coupling t-J model but with a three-site term(Nature communications 5, 3314 (2014)). However we show that hardening effect is a signature of strong coupling physics even without including this extra term. By considering the t-t'-t"-J model and using the Slave-Boson (SB) mean field theory, we obtain, via the spin-spin susceptibility, the spin excitations in qualitative agreement with the experiments. These anomalies is mainly due to the doping-dependent bandwidth. We further discuss the interplay between particle-hole-like and paramagnon-like excitations in the RIXS measurements.Comment: 7 pages, 6 figure

Women in Politics: A New Instrument for Studying the Impact of Education on Growth

This paper tests the growth model of distance to the technological frontier, which states that the closer an economy is to the frontier, the higher the relative importance of innovation relative to imitation as a source of productivity growth. Hence, an economy closer to the technological frontier should invest more in skilled labor since innovation is a skill-intensive activity. I use the proportion of female legislators as an instrument for skilled labor, in contrast to Vandenbussche, Aghion, and Meghir (2006) who used lagged educational expenditures. The results with the new instrument are consistent with the theoretical prediction and the previous results of Vandenbussche, Aghion, and Meghir (2006).distance to the technological frontier; women in politics

Do Gender Quotas Influence Women’s Representation and Policies?

This paper investigates the effect of applying gender quotas on policy decisions. I first examine the effect of gender quotas on the representation of female legislators, study the correlation between gender quotas and different types of government expenditures, and then use quotas as an instrument for the proportion of female legislators to investigate the effect of female legislators on policy outcomes. The results show that an increase in the share of female legislators by one percentage point increases the ratio of government expenditure on health and social welfare to GDP by 0.18 and 0.67 percentage points, respectively. The robustness check supports that the effect of quotas on female legislators is likely to be translated into the influence of female policymakers on social welfare.female legislator; gender quotas; policy outcomes

Female Policymaker and Educational Expenditure: Cross-Country Evidence

This paper investigates the influence of women in politics on decision-making using public educational expenditures as the outcome of interest. The results suggest that an increase in the share of female legislators by one percentage point increases the ratio of educational expenditures to GDP by 0.028 percentage points. I then consider some contexts, on which the influence of female legislators may depend. The effect of female legislators on educational policies is strengthened accounting for forms of government, but not influenced by left-wing government, electoral rules, parliamentary system and non-marriage. Moreover, this study supports the hypothesis that the identity of the legislator matters for policy.Education; female legislator; political economy