Interference dislocations adjacent to emission spot

TL;DR

The paper investigates interference dislocations adjacent to an emission spot in exciton emission from a WSe2 monolayer and interlayer excitons in MoSe2/WSe2, using shift-interferometry in a Mach-Zehnder interferometer. A theoretical model treats the emission-spot as a sum of incoherent point sources with spatially varying intensity, yielding an interference pattern whose adjacent dislocations arise from a moiré pattern created by the combined emission from constituent parts. Simulations show that these adjacent dislocations are robust to emission-spot shapes (Gaussian or Lorentzian) and spot size, aligning with experimental observations. Importantly, coherence between different parts of the emission spot is not required, indicating a classical moiré origin and distinguishing these features from vortex-based or long-range condensate dislocations.

Abstract

We studied interference dislocations (forks) adjacent to an emission spot in an interference pattern. The adjacent interference dislocations are observed in emission of excitons in a monolayer transition metal dichalcogenide and in emission of spatially indirect excitons, also known as interlayer excitons, in a van der Waals heterostructure. The simulations show that the adjacent interference dislocations appear due to the moiré effect in combined interference patterns produced by constituting parts of the emission spot. The adjacent interference dislocations can appear in interference images for various spatially modulated emission patterns.

Figures (4)

• Figure 1: Adjacent interference dislocations in interference pattern for excitons in WSe$_2$ monolayer. (a, b) Measured interference pattern $I(x, y)$ for the shift $\delta x = - 1.4$$\mu$m (a) and $\delta x = 1.4$$\mu$m (b). (c) The exciton emission spot. The adjacent interference dislocations are observed close to the exciton emission spot.
• Figure 2: Adjacent interference dislocations in interference pattern for indirect excitons (IXs) in MoSe$_2$/WSe$_2$ heterostructure. (a, b) Measured interference pattern $I(x, y)$ for the shift $\delta x = - 1.4$$\mu$m (a) and $\delta x = 1.4$$\mu$m (b). (c) The IX emission spot. The adjacent interference dislocations are observed close to the IX emission spot.
• Figure 3: Simulated exciton interference pattern with adjacent interference dislocations. (a, b) Interference pattern $I_{\rm interf}(x, y)$ for the emission spot generated by the Gaussian-shape exciton source with width $\sigma = 0.7$$\mu$m: $P(\mathbf{r}_{\rm s}) = e^{-|\mathbf{r}_{\rm s}|^2/2\sigma^2}$. The shift $\delta x = - 1.4$$\mu$m (a) and $\delta x = 1.4$$\mu$m (b). (c) The emission spot $I_{\rm em}(x, y)$ generated by this exciton source. The adjacent interference dislocations are located close to the emission spot.
• Figure 4: Simulated exciton interference patterns for various emission spots. (a, b) Interference pattern $I_{\rm interf}(x, y)$ for the emission spot generated by the Lorentzian-shape exciton source with width $\sigma = 0.7$$\mu$m: $P(\mathbf{r}_{\rm s}) = 1/(|\mathbf{r}_{\rm s}|^2 + \sigma^2)$. The shift $\delta x = - 1.4$$\mu$m (a) and $\delta x = 1.4$$\mu$m (b). (c) The separation of the simulated interference dislocations from the spot center vs. the spot size. The points (triangles) correspond to Gaussian-shape (Lorentzian-shape) exciton sources with width $\sigma$.