Excitonic effects in two-dimensional semiconductors: Path integral Monte Carlo approach

Abstract

One of the most striking features of novel 2D semiconductors (e.g., transition metal dichalcogenide monolayers or phosphorene) is a strong Coulomb interaction between charge carriers resulting in large excitonic effects. In particular, this leads to the formation of multi-carrier bound states upon photoexcitation (e.g., excitons, trions and biexcitons), which could remain stable at near-room temperatures and contribute significantly to optical properties of such materials. In the present work we have used the Path Integral Monte Carlo methodology to numerically study properties of multi-carrier bound states in 2D semiconductors. Specifically, we have accurately investigated and tabulated the dependence of single exciton, trion and biexciton binding energies on the strength of dielectric screening, including the limiting cases of very strong and very weak screening. The results of this work are potentially useful in the analysis of experimental data and benchmarking of theoretical and computational models.

Binding energies and spatial structures of small carrier complexes in monolayer transition-metal dichalcogenides via diffusion Monte Carlo

“…Although DMC has previously been used to calculate ground-state properties for trions interacting with a purely logarithmic potential [39], to the best of our knowledge it has not been used to calculate trion properties with the more realistic electron-hole interaction above, nor has it been used to calculate the properties of biexcitons. It should be noted that while the present work was underway, a numerically exact finite temperature path integral Monte Carlo (PIMC) study of excitons, trions, and biexcitons using the full Keldysh effective potential appeared [50]. While we believe that DMC is a more direct method than PIMC for the study of what are essentially ground state properties, we note that the results presented here are in quantitative agreement with those presented earlier in Ref.…”

“…While we believe that DMC is a more direct method than PIMC for the study of what are essentially ground state properties, we note that the results presented here are in quantitative agreement with those presented earlier in Ref. [50], yielding ground state energies that lie below those of Ref. [50] by fractions of a percent.…”

“…[50], yielding ground state energies that lie below those of Ref. [50] by fractions of a percent. On the other hand, the goals of this work are somewhat distinct from those of Ref.…”

Room temperature observation of biexcitons in exfoliated WS2 monolayers

“…From Figure 2(c) this energy difference is 65 meV taking into account the small red shift of the XX/D peak after 2 kW/cm 2 . Recent theoretical calculations accurately predict the binding energies of excitons and trions within 2D materials, but they fail to do so for biexcitons [33][34][35][36][37][38][39] .The models predict that the biexciton is less strongly bound than the trion, in contradiction to experimental findings 25,27 . However, the models reconcile this discrepancy by suggesting that the experimentally observed states may actually be those of excited biexcitons, as opposed to ground state biexcitons 25 .…”

“…From Figure 2(c) this energy difference is 65 meV taking into account the small red shift of the XX/D peak after 2 kW/cm 2 . Recent theoretical calculations accurately predict the binding energies of excitons and trions within 2D materials, but they fail to do so for biexcitons [33][34][35][36][37][38][39] .…”