Excitonic transport driven by repulsive dipolar interaction in a van der Waals heterostructure

Abstract

Dipolar bosonic gases are currently the focus of intensive research due to their interesting many-body physics in the quantum regime. Their experimental embodiments range from Rydberg atoms to GaAs double quantum wells and van der Waals heterostructures built from transition metal dichalcogenides. Although quantum gases are very dilute, mutual interactions between particles could lead to exotic many-body phenomena such as Bose-Einstein condensation and high-temperature superfluidity. Here, we report the effect of repulsive dipolar interactions on the dynamics of interlayer excitons in the dilute regime. By using spatial and time-resolved photoluminescence imaging, we observe the dynamics of exciton transport, enabling a direct estimation of the exciton mobility. The presence of interactions significantly modifies the diffusive transport of excitons, effectively acting as a source of drift force and enhancing the diffusion coefficient by one order of magnitude. The repulsive dipolar interactions combined with the electrical control of interlayer excitons opens up appealing new perspectives for excitonic devices.

Molding 2D Exciton Flux toward Room Temperature Excitonic Devices

“…In contrast, owing to the electron-hole separation and the aligned electric dipole moments for the interlayer exciton (IX) in heterostructure, the net repulsive Coulomb interaction should be included in the exciton diffusion, which can be consolidated by the blueshift in the IX energy with increasing excitation laser power. [40,46] The repulsive exciton interaction is composed of dipolar repulsion and exchange interaction. [50] The exchange interaction reduces with the increased separation of electrons and holes, and becomes negative when the vertical separation is larger than the Bohr radius.…”

Electrical control of excitons in GaN/(Al,Ga)N quantum wells

“…Indirect excitons (IXs) are bound pairs of an electron and a hole confined in separated quantum layers, either semiconductor quantum wells (QWs) 1,2 , or various transition metal dichalcogenides (TMD) monolayers [3][4][5][6] . Due to their permanent dipole moment, IXs can be controlled in-situ by voltage [6][7][8] , can travel over large distances 5,[9][10][11][12][13] , and can cool below the temperature of quantum degeneracy before recombination [14][15][16][17][18][19][20][21][22][23][24] . Due to these properties, IXs are considered as a promising platform for the development of excitonic devices 25,26 .…”

Long-Range Propagation of Indirect Excitons in MoSe2/WSe2 van der Waals Heterostructure

“…The IX binding energies in TMD heterostructures reach hundreds of meV [26,37], making IXs stable at room temperature [38,39]. Propagation of both DXs in TMD monolayers [40][41][42][43][44][45][46] and IXs in TMD heterostructures [47][48][49][50][51][52][53][54][55] is intensively studied. However, in spite of long IX lifetimes in the TMD heterostructures, orders of magnitude longer than DX lifetimes, a relatively short-range IX propagation with d 1/e up to ∼ 3 µm was reported in the studies of TMD heterostructures.…”

“…Moiré superlattices enable studying excitons in in-plane potentials, the period b ≈ a/ √ δθ 2 + δ 2 is typically in the ∼ 10 nm range (a is the lattice constant, δ the lattice mismatch, δθ the twist angle deviation from nπ/3, n is an integer) [61][62][63][64][65][66], and the moiré potential landscapes can be affected by atomic reconstruction [67][68][69][70][71]. However, for the exciton propagation, the moiré potentials can cause an obstacle and, along with in-plane disorder potentials, can be responsible for limiting the IX propagation distances to d 1/e ∼ 3 µm in the TMD heterostructures [47][48][49][50][51][52][53][54][55].…”