Self-Trapped Interlayer Excitons in van der Waals Heterostructures

Abstract

The self-trapped state (STS) of the interlayer exciton (IX) has aroused enormous interest owing to its significant impact on the fundamental properties of the van der Waals heterostructures (vdWHs). Nevertheless, the microscopic mechanisms of STS are still controversial. Herein, we study the corrections of the binding energies of the IXs stemming from the exciton−interface optical phonon coupling in four kinds of vdWHs and find that these IXs are in the STS for the appropriate ratio of the electron and hole effective masses. We show that these self-trapped IXs could be classified into type  with the increasing binding energy in the tens of millielectronvolts range, which are very agreement with the red-shift of the IX spectra in experiments, and type  with the decreasing binding energy, which provides a possible explanation for the blue-shift and broad line width of the IX's spectra at low temperatures. Moreover, these two types of exciton states could be transformed into each other by adjusting the structural parameters of vdWHs. These results not only provide an in-depth understanding for the self-trapped mechanism but also shed light on the modulations of IXs in vdWHs.

Interlayer Exciton–Phonon Bound State in Bi2Se3/Monolayer WS2 van der Waals Heterostructures

“…It should be noted that the FCP can be applied to crystalline solids when excitons self-localize and a strong electron–phonon coupling is present. , Evidence is emerging that conditions in TMD-based van der Waals heterostructures may be conducive to self-localized excitons, , raising the prospect that the free-excitons in WS 2 are self-trapping when forming the exciton–phonon bound state. Further research is required to determine the model that best describes the system.…”

Self-trapped excitons in soft semiconductors

“…The formation of different interlayer exciton types originated from the different decay rates of the Coulomb potential correction (Δ E c ), self-trapping energy (Δ E s ), and the total correction of the binding energy (Δ E b ) (shown in Fig. 6B); 118 the STEs in van der Waals heterojunctions have already been experimentally proved. 158,159 More specifically, in the epitaxial grown SnSe 2 /STO heterojunction, a nearly flat in-gap band that correlated with a significant charge modulation in real space was systematically observed by performing angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) measurements (Fig.…”

“…STEs have been observed in a variety of materials, such as perovskite, 3,24 Metal chalcogenides, 43,114–117 van der Waals heterostructures, 118 and two-dimensional organic semiconductors. 119–122 Normally, the amorphization, disorder, and lattice expansion are ascribed to the formation of STEs.…”

“…150,154–156 However, in 2D materials with soft lattices, the strong EPC could also trigger the formation of STEs. 80,118,157–160 Deng et al theoretically studied the properties of STS, which were imposed by the interlayer excitons in the MoS 2 /hBN van der Waals heterostructures with four different kinds of configurations. 118 The interlayer excitons had three types due to the energy-shifting effect (Fig.…”

Self‐Trapped Exciton States in Metal Halide Perovskites van der Waals Heterostructures

“… is the phonon energy with the ν th branch of the effective frequency . In the frame of the dielectric continuum model, [ 33–36 ] these effective IOP modes, coupling strongly with excitons in this kind of vdW heterostructure, are determined by in which these IOP are actually the joint phonon modes depending on the intrinsic longitudinal optical (LO) and transverse optical (TO) phonon modes of the monolayer MHP (, ) and encapsulation layers (, ). Since there are two branches for LO and TO phonons in each encapsulation layer and thus four different IOP modes () are obtained from Equation ().…”