Room-Temperature Amplified Spontaneous Emission in Two-Dimensional WS2 beyond Exciton Mott Transition

The highly excited electron-hole plasma (EHP) phase is a natural platform for studying amplified spontaneous emission (ASE), yet research into the many-body physics of EHP and ASE in twodimensional (2D) semiconductors remains limited. Here, we report the first observation of ASE from EHP in 2D semiconductors, evidenced by an unusually sharp enhancement of emissions in suspended bilayer WS2 at a threshold power, confirming the transient differential transmission measurements under continuous wave excitations. We modeled the optical dielectric response of varying densities of excited carriers and accurately reproduced the observed emission features across different electron-hole phases from bilayer WS2 over a simple Fabry-Pe<acute accent>rot cavity. This, together with spatially resolved emissions, confirmed that ASE stems from the degenerate EHP. Our analysis highlights the crucial role of many-body interactions in achieving ASE in 2D EHP. This Letter provides a new insight into the rich physics in EHP and expands the potential for developing advanced 2D semiconductor based optoelectronic devices.