James Wadsley
McMaster University

Abstract

Galaxies are not as isolated as they may appear: they exchange huge amounts of material with their nearby environment.  Even typical disk galaxies contain only 1/4 the expected stars and gas (baryons) expected from their dark matter.   Smaller galaxies can contain far less.    These exchanges have many consequences, such as polluting nearby space with hot gas and metals, which can be observed as quasar absorption lines out to large distances.   There is a long list of ideas for how galaxies limit their gas and star content,  including pushing gas out with stellar feedback such as supernovae,  AGN, cosmic rays and radiation driven processes.     Violent outflows even have the potential to modify the dark matter profile.  There are also more subtle mechanisms, such as not letting the gas cool and accrete in the first place.   I present recent simulations using on-the-fly radiative transfer to better model gas in and around galaxies and the consequences for their evolution. I show the impact on dwarf galaxies in particular.

Timbits, coffee, tea will be served in STI A before the colloquium.

Cheng Chin
James Franck institute, Enrico Fermi institute,
Department of Physics, University of Chicago

Abstract

A central question in cosmology is to understand the inflation process. While primordial fluctuations are considered quantum in origin, the observed cosmic microwave background anisotropy is so far well described by classical Gaussian field. What would be the observables of quantum correlations? Can quantum optics and quantum simulation offer hints on the emergence of non-Gaussianity and unitarity of the inflation dynamics?

Timbits, coffee, tea will be served in STI A before the colloquium.

Haruki Sanada,
NTT Basic Research Laboratories

Abstract

Transition-metal dichalcogenides (TMDs) monolayers have attracted attention as a platform for hybridizing spintronics, valleytronics, and optoelectronics because of their optically accessible characteristic electronic structures coupled with spin and valley degrees of freedom. Suspending such monolayers on patterned substrates enables us to avoid local impurities and interfacial inhomogeneous strain due to the contact of the monolayer and substrates, allowing us to expect better electrical and optical properties. The suspended monolayers have been studied mainly by photoluminescence (PL) spectroscopy, which limits the analysis to short-lived (~ps) radiative excitons. Here, we employed pump-probe Kerr rotation (KR) spectroscopy to investigate the dynamics of the spin-valley polarization with longer lifetime (> ns) generated in a suspended WSe2 monolayer. The KR dynamics significantly depends on the back gate voltage and the probe wavelength, which provides a clue for a deeper understanding of origin of the spin valley polarization. The results indicate that our approach using the KR measurements on gate-tunable suspended TMD monolayers provides multiple tuning knobs for monitoring and controlling the spin-valley states of the exciton complexes in a single sample.