Strain-Induced Trapping of Indirect Excitons in MoSe₂/WSe₂ Heterostructures

Abstract

Understanding and control of excitons in transition metal dichalcogenide (TMD) materials are essential for the exploration of the rich many-body physics in TMDs and their applications in photonic and optoelectronic devices. Local strain modulation has been utilized as an effective approach for creating potential traps and localizing intralayer excitons in TMD monolayers. Here, we investigate the effect of strains on indirect excitons in TMD heterostructures. The emergence of narrow spectral peaks from the strained sites together with their drastically reduced lifetimes indicates the formation of potential traps in the heterostructures and the trapping of indirect excitons in them. The absence of photon-antibunching from these trapped indirect excitons further reveals their weak localization in the potential traps. Our study indicates that, compared to the case of intralayer excitons, narrower potential traps are required for obtaining highly localized indirect excitons due to their unique properties. These findings have important implications for creating long-wavelength quantum emitters in TMD heterostructures and the exploration of indirect exciton condensation and motion in TMDs.

Site-controlled interlayer coupling in WSe2/2D perovskite heterostructure

“…The blue shift of PL of IXs in WSe 2 /MoSe 2 heterobilayers has also been reported by reducing the gap between the two layers to enhance interlayer coupling, similar to our scenario [29]. It is assumed that monolayer WSe 2 exhibits a tent-like shape around the pillar, as reported in several studies [17,32,37]. Consequently, the gap between WSe 2 and (iso-BA) 2 PbI 4 is shortened on top of the pillar, yielding enhanced interlayer coupling.…”

“…It is worth noting that the exciton funneling effect can also increase the PL intensity, in which the strain of the pillar creates a potential well (energy minimum) and the excitons can be drifted from a flat unstrained region to the potential well. Nevertheless, the trap energy level is lower than CB for the funneling effect; thus, IX emission should be red shifted as reported previously [31,32,36], which contradicts the blue shift in our measurement. Thus, exciton funneling is excluded.…”

“…For example, strong coupling of WSe 2 /MoSe 2 heterobilayers could be achieved by applying high pressure to reduce the gap between constituent layers [29]. It has also been demonstrated that the resonance wavelength, exciton localization, and anisotropy of IXs could be largely tuned via strain [30][31][32][33]. In addition, moiré potential could modify IX dipole-dipole interactions [15,34].…”

Self-trapped interlayer excitons in van der Waals heterostructures

“…For example, TMDC bilayer heterostructures with twist-angle induces spatially periodic moiré superlattice potential that can trap IX, which has been predicted by several theoretical studies [23][24][25][26][27][28] and confirmed by a series of experiments [5,[29][30][31][32][33][34][35]. Strain has also been proposed as an effective way to trap IX, in which the band structures of TMDC heterostructures are modified by strain, resulting in the static potential well [16,[36][37][38]. The spatially varying electric fields enable the localization of IX due to its permanent dipole moment [10,39,40], where the deterministic placement and control of a single trapped IX has been achieved [39].…”

“…The interlayer excitons (IXs) are formed by bound pairs of electrons and holes spatially separated in two different two-dimensional (2D) semiconductor materials of van der Waals heterostructures (vdWHs) [1][2][3][4][5][6][7][8][9][10][11][12], such as those in 2D transition metal dichalcogenides (TMDC) bilayer with a type-II band alignment. The spatial separation between the electron and hole allows achieving long IX lifetimes, orders of magnitude longer than lifetimes of intralayer excitons in TMDC monolayers [8,11,[13][14][15][16][17][18]. This longer lifetime, combined with the large binding energy, has enabled the exploration of the rich many-body physics of IX and their applications in tunable photonic and optoelectronic devices [8,17,[19][20][21][22].…”