Exciton fission in monolayer transition metal dichalcogenide semiconductors

Abstract

When electron-hole pairs are excited in a semiconductor, it is a priori not clear if they form a plasma of unbound fermionic particles or a gas of composite bosons called excitons. Usually, the exciton phase is associated with low temperatures. In atomically thin transition metal dichalcogenide semiconductors, excitons are particularly important even at room temperature due to strong Coulomb interaction and a large exciton density of states. Using state-of-the-art many-body theory, we show that the thermodynamic fission–fusion balance of excitons and electron-hole plasma can be efficiently tuned via the dielectric environment as well as charge carrier doping. We propose the observation of these effects by studying exciton satellites in photoemission and tunneling spectroscopy, which present direct solid-state counterparts of high-energy collider experiments on the induced fission of composite particles.

Exciton diffusion in monolayer semiconductors with suppressed disorder

“…15 While it is indeed often the case, there is nevertheless a number of scenarios where large populations of free electrons and holes can be expected . 53 For example, at high excitation densities beyond the Mott-transition threshold, the excitons cease to be bound states due to screening and Pauli-blocking [51][52][53]62 leading to the emergence of a dense electron-hole plasma. Interestingly, also at sufficiently low densities the occupation of free carrier states can be favored and the formation of the excitons suppressed.…”

Giant and Tunable Optical Nonlinearity in Single‐Crystalline 2D Perovskites due to Excitonic and Plasma Effects

“…This can be ascribed to the large oscillator strength of the weakly damped n = 1 systems facilitating the generation of high exciton densities near resonance. The large exciton populations can lead to efficient dipolar screening and phase‐space filling, reducing and the effective bandgap (i.e., bandgap renormalization) and hence, triggering a Mott transition (MT) to a metal‐like ionized plasma . Such an exciton MT in 2D systems has previously been observed only at sufficiently low temperature (typically few to tens of Kelvin) and exciton densities on the order of 10 10 –10 12 cm −2 .…”

Theory of Exciton–Exciton Interactions in Monolayer Transition Metal Dichalcogenides

“…These interactions have been introduced as the k ‐space equivalent of the Dexter transfer . For large momentum transfer on the order of the reciprocal lattice vector the Rytova–Keldysh potential is not valid anymore and the effective screening must be adapted to density functional theory calculations …”