Platform for Electrically Pumped Polariton Simulators and Topological Lasers

Two-dimensional electronic materials such as graphene and transition metal dichalgenides feature unique electrical and optical properties due to the conspirative effect of band structure, orbital coupling, and crystal symmetry. Synthetic matter, as accomplished by artificial lattice arrangements of cold atoms, molecules, electron patterning, and optical cavities, has emerged to provide manifold intriguing frameworks to likewise realize such scenarios. Exciton polaritons have recently been added to the list of promising candidates for the emulation of system Hamiltonians on a semiconductor platform, offering versatile tools to engineer the potential landscape and to access the nonlinear electro-optical regime. In this work, we introduce an electronically driven square and honeycomb lattice of exciton polaritons, paving the way towards real world devices based on polariton lattices for on-chip applications. Our platform exhibits laserlike emission from high-symmetry points under direct current injection, hinting at the prospect of electrically driven polariton lasers with possibly topologically nontrivial properties.

Figure 1

(a) Schematic of the investigated device showing the half-etched polariton lattice, planarized with benzocyclobutene with top and bottom electrical contacts. (b) Scanning electron microscope (SEM) image of the processed device with a view tilted above the cleaved edge, cutting the device in half. A gold contact (yellow) has been deposited on an etched two-dimensional lattice (red) in order to inject a current into the microcavity structure. The quantum wells (QWs) have been placed in the field maximum inside a $\lambda$ cavity (cyan). The $n$ contact is deposited on the plane backside of the GaAs substrate. To avoid etching damage to the QWs, the etching depth has been adjusted in order to stop close above the cavity region. (c),(d) SEM images of the investigated lattice devices in top view configuration. The deposited gold contact (yellow) surrounds the etched lattices (red) with an overlap of one to two lattice constants. The whole lattice field has an edge length of $\sim 50\mu \mathrm{m}$ with (c) depicting the investigated square lattice and (d) the honeycomb lattice.

Figure 2

(a) Scanning electron microscope image of the investigated honeycomb lattice and the corresponding reciprocal space (b). (c)–(e) PL dispersion in the $K\text{−}\mathrm{\Gamma }\text{−}{K}^{\prime }$ (c), $K^{\prime }\text{−}M\text{−}K$ (d) and $K\text{−}K\text{−}K$ direction (e) of the first Brillouin zone (BZ), showing the distinct Dirac cone dispersion around the $K$ points. The dashed line is a tight-binding (TB) calculation reproducing the $S$ band of the dispersions. The excitation density amounts to $\sim 10\mathrm{W}{\mathrm{cm}}^{-2}$. (f) Hyperspectral imaging of the first BZ with the peak positions fitted to the dispersion spectra (blue) and the TB simulation of the lower (red) and upper $S$ band (yellow). (g) Energy cut in reciprocal space at the center of the $S$ band, showing a clear honeycomb geometry with the $K$ and $K^{\prime }$ points. (h)–(j) EL emitted by the very same honeycomb lattice in the $K\text{−}\mathrm{\Gamma }\text{−}{K}^{\prime }$ (h), $K^{\prime }\text{−}M\text{−}K$ (i), and in the $K\text{−}K\text{−}K$ (j) direction of the first BZ. The TB calculation uses the same fit parameter as for the PL measurement.

Figure 3

(a) Luminescence dispersion of the honeycomb lattice in $M\text{−}\mathrm{\Gamma }\text{−}M$ direction under combined electrical and optical excitation. The constant laser power amounts to $90\mathrm{W}{\mathrm{cm}}^{-2}$, while the injected current density amounts to $150\mathrm{A}/{\mathrm{cm}}^2$ here. With increasing current density a sharp emission in $k$ space as well as in energy is seen at the $\mathrm{\Gamma }$ point of the second Brillouin zone (BZ) at the bottom of the $P$ band. (b) Corresponding luminescence dispersion of the honeycomb lattice at a constant energy of 1.508 eV, as indicated by the green line in (a). The first BZ and the relevant high-symmetry points are highlighted. (c) Extracted intensity of the relevant mode under combined optical and electrical excitation. A nonlinear increase of the emission intensity is seen around a threshold density of $\sim 100\mathrm{A}/{\mathrm{cm}}^2$.