Financial Development and Innovation-led Growth::Is Too Much Finance Better?

We show that the expansion of financial sector may hurt innovative activities and hence the innovation-led growth, using data on 50 countries over the 1990–2016 period. Countries with higher level of financial development are found to have a smaller positive or insignificant effect on innovation. The marginal effect of innovation on growth is a decreasing function of financial development. Using a dynamic panel threshold method we re-examine the possible non-linearity between finance, innovation and growth. We find that innovation exhibits an insignificant effect on output growth when credit to the private sector exceeds a threshold level of about 60% as a share of GDP. These results are not driven by banking crises, the long run effect of 2007–2008 financial crisis, or the ongoing European sovereign debt crisis

Essays in financial development, innovation, and economic growth

My dissertation comprises two chapters. The first chapter uses country-level data and examines the diminishing effect of financial development on innovation, and how "too much finance" affects economic growth through this diminishing effect. The second chapter uses industry-level data aggregated from firm-level data to examine the nonlinear effect of financial development on innovation as well as explores the channels.The first chapter explores the nonlinear effect of financial development on innovation and growth. We show that the expansion of the financial sector may hurt innovative activities and hence the innovation-led growth, using data on 50 countries over the 1990-2016 period. Countries with a higher level of financial development are found to have a smaller positive or insignificant effect on innovation. The marginal effect of innovation on growth is a decreasing function of financial development. Using a novel dynamic panel threshold method we examine the possible nonlinearity between finance, innovation, and growth. We find that innovation exhibits an in- significant effect on output growth when credit to the private sector exceeds the level of 60% as a share of GDP. These results are not driven by banking crises, the long-run effect of the 2007-2008 financial crisis, or the ongoing European sovereign debt crisis.This second chapter studies the nonlinear effect of financial development on innovation as well as the potential channels, primarily using a unique database constructed from the Worldscope Fundamentals Annual from 1980 to 2017. Our results can be summarized as follows. 1) Using a broad index of financial development, we find that the overall effect on innovation is a diminishing one, and the patterns are robust under different robustness checks. 2) We also have documented that, using traditional one-dimension indicators of financial development for both equity and credit markets, equity markets have a kick-in effect on innovation, while the diminishing effects still hold for credit markets. 3) We find industry-specific effects. In particular, the equity market development has a diminishing effect on innovations in high-technology industries, while credit market development has a diminishing effect on innovations in non-high-technology industries. 4) We show that the nonlinear effect of financial development on market competition serves as a potential channel through which finance affects innovation nonlinearly. 5) Our last finding is that the effect is heterogeneous across different stages of development

Dynamic screening of quasiparticles in WS2_2 monolayers

We unravel the influence of quasiparticle screening in the non-equilibrium exciton dynamics of monolayer WS$_2$. We report pump photon energy-dependent exciton blue/red-shifts from time-resolved-reflectance contrast measurements. Based on a phenomenological model, we isolate the effective impact of excitons and free carriers on the renormalization of the quasi-free particle band gap, exciton binding energy and linewidth broadening. This work provides a comprehensive picture of the competing phenomena governing the exciton dynamics in WS$_2$ upon photoexcitation

Energy-efficient domain wall motion governed by the interplay of helicity-dependent optical effect and spin-orbit torque

Spin-orbit torque provides a powerful means of manipulating domain walls along magnetic wires. However, the current density required for domain wall motion is still too high to realize low power devices. Here we experimentally demonstrate helicity-dependent domain wall motion by combining synchronized femtosecond laser pulses and short current pulses in Co/Ni/Co ultra-thin film wires with perpendicular magnetization. Domain wall can remain pinned under one laser circular helicity while depinned by the opposite circular helicity. Thanks to the all-optical helicity-dependent effect, the threshold current density due to spin-orbit torque can be reduced by more than 50%. Based on this joint effect combining spin-orbit torque and helicity-dependent laser pulses, an optoelectronic logic-in-memory device has been experimentally demonstrated. This work enables a new class of low power spintronic-photonic devices beyond the conventional approach of all-optical switching or all-current switching for data storage.Comment: 21 pages, 5 figure