Spatiotemporal dynamics of Coulomb-correlated carriers in semiconductors

Abstract

When the excitation of carriers in real space is focused down to the nanometer scale, the carrier system can no longer be viewed as homogeneous and ultrafast transport of the excited carrier wave packets occurs. In state-of-the-art semiconductor structures like low-dimensional heterostructures or monolayers of transition metal dichalcogenides, the Coulomb interaction between excited carriers becomes stronger due to confinement or reduced screening. This demands a fundamental understanding of strongly interacting electrons and holes and the influence of Coulomb correlations. To study the corresponding particle dynamics in a controlled way we consider a system of up to two electron-hole pairs exactly within a wave function approach. We show that the excited wave packets contain a non-trivial mixture of free particle and excitonic states. We further scrutinize the influence of Coulomb interaction on the wave packet dynamics revealing its different role for below and above band-gap excitation.

Electron Dynamics in a Two-Dimensional Nanobubble: A Two-Level System Based on Spatial Density

“…Because we discuss the capture of electrons, we focus on the Fröhlich coupling which is particularly efficient in these materials . We stress that we focus on the low-density regime, so that Pauli-blocking or Coulomb-induced effects can be neglected.…”

Theory of coherent pump–probe spectroscopy in monolayer transition metal dichalcogenides

“…The coupled differential Heisenberg equations describing the nonlinear optical response are truncated to third order in the exciting electro magnetic field O (E 3 ) [65][66][67][68][69][70]. In this limit, the relevant quantities are the optically addressable interband transitions c † ξ,s,k v ξ,s,k , building up a macroscopic polarization, which also couples to four-point correlation functions beyond a Hartree-Fock description [71,72], see figure 2: In order to find a numerically feasible approach, the interband transitions are expanded in terms of excitonic wavefunctions (section 2.1) and the four-particle correlations, equation (1), in a set of corresponding biexcitonic wavefunctions, including both bound and continuum states with respect to the energetically lowest 1s excitonic resonances (section 2.2). In particular, besides bound biexcitons, the biexcitonic continuum of exciton-exciton scattering states is required to get a quantitative understanding.…”

Electrically tunable dipolar interactions between layer-hybridized excitons

“…43 The considered initial exciton density is below the exciton Mott transition, which is estimated to occur at densities ∼7 × 10 12 cm −2 in WSe 2 homobilayers 60 and we neglect the impact of free carriers on the transport. 61 Moreover, we assume the diffusion coefficient D = 0.3 cm 2 s −1 and the exciton life-time τ = 500 ps as obtained from a recent experiment on the same homobilayer. 62 Note that there is no moiré potential which could trap excitons and slow down their propagation, 28,[63][64][65] as we are considering untwisted homobilayers with no lattice mismatch.…”