Microscopic lattice for two-dimensional dipolar excitons

Abstract

We report a two-dimensional artificial lattice for dipolar excitons confined in a GaAs double quantum well. Exploring the regime of large fillings per lattice site, we verify that the lattice depth competes with the magnitude of excitons repulsive dipolar interactions to control the degree of localisation in the lattice potential. Moreover, we show that dipolar excitons radiate a narrow-band photoluminescence, with a spectral width of a few hundreds of µeV at 340 mK, in both localised and delocalised regimes. This makes our device suitable for explorations of dipolar excitons quasicondensation in a periodic potential.

Quasicondensation of Bilayer Excitons in a Periodic Potential

“…Figure 4 shows that the transition between this array of droplets and the extended quasicondensate (V 0 ∼ 0) passes then through a normal incoherent exciton gas which is not localized by the lattice potential (see Ref. [6]). Such transition does not correspond to the framework of Josephson coupled array of condensates, but rather suggests that coherence is destroyed due to a renormalization of the exciton effective mass, which yields a critical phase-space density exceeding our experimental conditions.…”

“…The phase-space density D is then around 12 corresponding to a chemical potential μ of about 0.8 meV, i.e., well above the critical value D c ∼ 8 for exciton quasicondensation [11]. Thus, we explore how the lattice depth influences quantum statistical signatures, by continuously varying the height of the potential barrier V 0 separating the lattice sites [6].…”

“…They are possibly engineered in coupled GaAs quantum wells [4] or in van der Waals assemblies of transition metal dichalcogenides monolayers [5]. In the former case, excitons may be subject to an artificial lattice potential engineered by electrostatic gates [6,7] while in the latter case they naturally explore a periodic moiré potential [8][9][10]. For both systems, the Bose-Hubbard model is expected to provide an accurate low-energy description.…”

“…We study a square artificial lattice with spatial period L ¼ 3 μm, at a bath temperature T b set to 340 mK (see Ref. [6] for the characterization of our device). Indirect excitons are injected in the lattice potential using a 100-ns-long laser excitation, repeated at 1.5 MHz, resonant with the direct exciton absorption.…”

“…1(c) shows that excitons are strongly localized in the lattice sites which have a characteristic spatial extension of about 1 μm. This results in a modulation of the photoluminescence intensity, of around 20% along the horizontal axis of our device, with a 3 μm period [6]. To study spatially extended time coherence in the photoluminescence, we studied jg ð1Þ ð0; τÞj fixing the interference period to 4.5 μm, as in the measurements shown in Figs.…”