Patients with spontaneous CSF leak are more likely to be obese, have the diagnosis of OSA, and show thinning of their entire calvarium that is independent of BMI. These data suggest an additional obesity-associated intracranial process contributes to skull thinning.

A key feature of monolayer semiconductors, such as transition-metal dichalcogenides, is the poorly screened Coulomb potential, which leads to large exciton binding energy (E b ) and strong renormalization of the quasiparticle bandgap (E g ) by carriers. The latter has been difficult to determine due to cancellation in changes of E b and E g , resulting in little change in optical transition energy at different carrier densities. Here we quantify bandgap renormalization in macroscopic single crystal MoS 2 monolayers on SiO 2 using time and angle resolved photoemission spectroscopy (TR-ARPES). At excitation density above the Mott threshold, E g decreases by as much as 360 meV. We compare the carrier density dependent E g with previous theoretical calculations and show the necessity of knowing both doping and excitation densities in quantifying the bandgap. Atomically thin transition-metal dichalcogenide (TMDC) monolayers and heterojunctions are being broadly explored as model systems for a wide range of electronic, optoelectronic, and quantum processes. The commonly studied TMDC monolayers possess direct bandgaps in the visible to near-IR region [1-3]. Because of the strong many-body Coulomb interactions in monolayer TMDCs, both exciton binding energy (E b ) and bandgap renormalization energy are large [3]. The former lowers the optical transition energy by hundreds meV from E g , while thelatter decreases E g by similar amounts in the presence of charge carriers or excitons. The bandgap renormalization energy (ΔE g ) and decrease in exciton binding energy (ΔE b ) tend to be of similar magnitudes but counteract each other, leading to comparatively modest changes in optical transition energies [4,5]. Since the quasiparticle bandgap E g is the most fundamental quantity and is predicted to be exceptionally sensitive to carrier or exciton densities [4,6,7], there

Aside from band gap reduction, little is understood about the effect of the tin‐for‐lead substitution on the fundamental optical and optoelectronic properties of metal halide perovskites (MHPs), especially when transitioning from 3D to lower dimensional structures. Herein, we take advantage of the spectroscopic isolation of excitons in 2D MHPs to study the intrinsic differences between lead and tin MHPs. The exciton's spectral fine structure indicates a larger polaron binding energy in tin MHPs. Additionally, the electroabsorption responses of the 2D MHPs demonstrates that tin MHPs have exciton binding energies 1.5–2× lower than that of their lead counterparts. Despite the lower binding energy, the excitons in tin MHPs are more Frenkel‐like with small radii, small polarizabilities, and large dipole moments. These results are interpreted as consequences of small polaron formation and disorder‐induced dipole moments. This work highlights the wide range of intrinsic differences between lead and tin MHPs as well as the complexity of excited states in these systems.

A key feature of monolayer semiconductors, such as transition-metal dichalcogenides, is the poorly screened Coulomb potential, which leads to large exciton binding energy (Eb) and strong renormalization of the quasiparticle bandgap (Eg) by carriers. The latter has been difficult to determine due to cancellation in changes of Eb and Eg, resulting in little change in optical transition energy at different carrier densities. Here we quantify bandgap renormalization in macroscopic single crystal MoS2 monolayers on SiO2 using time and angle resolved photoemission spectroscopy (TR-ARPES). At excitation density above the Mott threshold, Eg decreases by as much as 360 meV. We compare the carrier density dependent Eg with previous theoretical calculations and show the necessity of knowing both doping and excitation densities in quantifying the bandgap. Atomically thin transition-metal dichalcogenide (TMDC) monolayers and heterojunctions are being broadly explored as model systems for a wide range of electronic, optoelectronic, and quantum processes. The commonly studied TMDC monolayers possess direct bandgaps in the visible to near-IR region [1-3]. Because of the strong many-body Coulomb interactions in monolayer TMDCs, both exciton binding energy (Eb) and bandgap renormalization energy are large [3]. The former lowers the optical transition energy by hundreds meV from Eg, while the latter decreases Eg by similar amounts in the presence of charge carriers or excitons. The bandgap renormalization energy (DEg) and decrease in exciton binding energy (DEb) tend to be of similar magnitudes but counteract each other, leading to comparatively modest changes in optical transition energies [4,5]. Since the quasiparticle bandgap Eg is the most fundamental quantity and

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