Excitonic Mott insulator in a Bose-Fermi-Hubbard system of moiré WS2/WSe2 heterobilayer.

Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a WS2/WSe2 heterobilayer device that hosts this hybrid particle density. We independently tune the fermionic and bosonic populations by electronic doping and optical injection of electron-hole pairs, respectively. This enables us to form strongly interacting excitons that are manifested in a large energy gap in the photoluminescence spectrum. The incompressibility of excitons is further corroborated by observing a suppression of exciton diffusion with increasing pump intensity, as opposed to the expected behavior of a weakly interacting gas of bosons, suggesting the formation of a bosonic Mott insulator. We explain our observations using a two-band model including phase space filling. Our system provides a controllable approach to the exploration of quantum many-body effects in the generalized Bose-Fermi-Hubbard model.

Twist-Dependent Tuning of Excitonic Emissions in Bilayer WSe2.

Monolayer (ML) transition metal dichalcogenides (TMDCs) have been rigorously studied to comprehend their rich spin and valley physics, exceptional optical properties, and ability to open new avenues in fundamental research and technology. However, intricate analysis of twisted homobilayer (t-BL) systems is highly required due to the intriguing twist angle (t-angle)-dependent interlayer effects on optical and electrical properties. Here, we report the evolution of the interlayer effect on artificially stacked BL WSe2, grown using chemical vapor deposition (CVD), with t-angle in the range of 0 ≤ θ ≤ 60°. Systematic analyses based on Raman and photoluminescence (PL) spectroscopies suggest intriguing deviations in the interlayer interactions, higher-energy exciton transitions (in the range of ∼1.6-1.7 eV), and stacking. In contrast to previous observations, we demonstrate a red shift in the PL spectra with t-angle. Density functional theory (DFT) is employed to understand the band-gap variations with t-angle. Exciton radiative lifetime has been estimated theoretically using temperature-dependent PL measurements, which shows an increase with t-angle that agrees with our experimental observations. This study presents the groundwork for further investigation of the evolution of various interlayer excitons and their dynamics with t-angle in homobilayer systems, critical for optoelectronic applications.

Ferroelectric Negative-Capacitance-Assisted Phase-Transition Field-Effect Transistor.

An enormous study is being carried out in the field of emerging steep slope devices, specifically on negative-capacitance-based and phase transition-based devices. This article investigates the action of ferroelectric (FE) and phase transition material (PTM) on a hybrid device, negative-capacitance-assisted phase transition FinFET (NC-PT-FinFET). We encounter several unique phenomena resulting from this unified action and provide valid arguments based on these observations. A significant enhancement in the differential gain and transconductance, a unique variation in the effect of PTM on drain-channel coupling, tunability of hysteresis across PTM by FE thickness( [Formula: see text]), and ultralow subthreshold slope (SS) by lowering both of its factors are some of the major outcomes of the NC-PT-FinFET. Focus is built on comprehending the individual role of FE and PTM in the intriguing features observed in every device performance parameter with the help of mathematical expressions and physical interpretations. Various tunable parameters present in this hybrid device widen its applicability in digital and memory applications.