Interlayer Exciton–Polaron in Atomically Thin Semiconductors (original) (raw)
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Exciton–phonon interactions in nanocavity-integrated monolayer transition metal dichalcogenides
npj 2D materials and applications, 2020
Cavity-integrated transition metal dichalcogenide excitons have recently emerged as a promising platform to study strong light-matter interactions and related cavity quantum electrodynamics phenomena. While this exciton-cavity system is typically modeled as coupled harmonic oscillators, to account for the rich solid-state environment the effect of excitonphonon interaction needs to be incorporated. We model the system by including a phenomenological deformation potential for exciton-phonon interactions and we elucidate the experimentally measured preferential coupling of the excitonic photoluminescence to the cavity modes reddetuned with respect to the exciton resonance. Furthermore, we predict and experimentally confirm the temperature dependence of this preferential coupling. By accurately capturing the exciton-phonon interaction, our model illuminates the potential of cavity-integrated transition metal dichalcogenides for development of low-power classical and quantum technologies.
Nature Communications, 2021
Monolayer transition metal dichalcogenide crystals (TMDCs) hold great promise for semiconductor optoelectronics because their bound electron-hole pairs (excitons) are stable at room temperature and interact strongly with light. When TMDCs are embedded in an optical microcavity, excitons can hybridise with cavity photons to form exciton polaritons, which inherit useful properties from their constituents. The ability to manipulate and trap polaritons on a microchip is critical for applications. Here, we create a non-trivial potential landscape for polaritons in monolayer WS2, and demonstrate their trapping and ballistic propagation across tens of micrometers. We show that the effects of dielectric disorder, which restrict the diffusion of WS2 excitons and broaden their spectral resonance, are dramatically reduced for polaritons, leading to motional narrowing and preserved partial coherence. Linewidth narrowing and coherence are further enhanced in the trap. Our results demonstrate the...
Exciton condensate in bilayer transition metal dichalcogenides: Strong coupling regime
Physical Review B, 2017
Exciton condensation in an electron-hole bilayer system of monolayer transition metal dichalcogenides is analyzed at three different levels of theory to account for screening and quasiparticle renormalization. The large effective masses of the transition metal dichalcogenides place them in a strong coupling regime. In this regime, mean field (MF) theory with either an unscreened or screened interlayer interaction predicts a room temperature condensate. Interlayer and intralayer interactions renormalize the quasiparticle dispersion, and this effect is included in a GW approximation. The renormalization reverses the trends predicted from the unscreened or screened MF theories. In the strong coupling regime, intralayer interactions have a large impact on the magnitude of the order parameter and its functional dependencies on effective mass and carrier density.
Ju l 2 01 7 Exciton condensate in bilayer transition metal dichalcogenides : strong coupling regime
2018
Bishwajit Debnath, Yafis Barlas, Darshana Wickramaratne, Mahesh R. Neupane, and Roger K. Lake Department of Electrical and Computer Engineering, University of California, Riverside, CA 92521, USA Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA Materials Department, University of California, Santa Barbara, CA 93106, USA Electronics Technology Branch, Sensors and Electron Devices Directorate, U. S. Army Research Laboratory, Adelphi, MD 20783, USA
Colloquium : Excitons in atomically thin transition metal dichalcogenides
Reviews of Modern Physics
Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here we review recent progress in our understanding of the excitonic properties in monolayer TMDs and lay out future challenges. We focus on the consequences of the strong direct and exchange Coulomb interaction, discuss exciton-light interaction and effects of other carriers and excitons on electron-hole pairs in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.
Excitons in atomically thin transition-metal dichalcogenides
CLEO: 2014, 2014
Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here we review recent progress in our understanding of the excitonic properties in monolayer TMDs and lay out future challenges. We focus on the consequences of the strong direct and exchange Coulomb interaction, discuss exciton-light interaction and effects of other carriers and excitons on electron-hole pairs in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.
Nature Nanotechnology, 2021
Two-dimensional semiconducting systems, such as quantum wells and transition metal dichalcogenides, are the foundations to investigate low dimensional light-matter interactions 1,2. To date, the study of elementary photoexcitation, namely the exciton, in 2D semiconductors with intrinsic magnetic order remains a challenge due to the lack of suitable material platforms 3,4. Here, we report an observation of excitons coupled to zigzag antiferromagnetic order in the layered antiferromagnetic insulator NiPS3 using both photoluminescence and optical reflection spectroscopy. The exciton exhibits a linewidth as narrow as ~350 µeV with near unity linear polarization in the photoluminescence spectrum. As the thicknesses of samples is reduced from five layers to bilayers, the photoluminescence intensity is drastically suppressed and eventually vanishes in monolayers, consistent with the calculated bandgap being highly indirect for both bilayer and monolayer 5. Furthermore, we observed strong linear dichroism over a broad spectra range, which shares the same optical anisotropy axis, being locked to the zigzag direction, as the exciton photoluminescence. Both linear dichroism and the degree of linear polarization in the exciton photoluminescence decrease as the temperature increases and become negligible above the Néel temperature. These observations suggest both optical quantities are probes of the symmetry breaking magnetic order parameter. In addition, a sharp resonance in the linear dichroism spectrum is observed with an energy near the exciton photoluminescence. There exist over ten exciton-A1g phonon bound states on its high energy side, which likely result from the strong modulation of the ligand-to-metal charge transfer energy by strong electron-lattice interactions. Our work establishes NiPS3 as a new 2D platform for exploring magnetoexciton physics with strong correlations, as well as a building block for 2D heterostructures for engineering physical phenomena with time reversal symmetry breaking.
Crystal phases of charged interlayer excitons in van der Waals heterostructures
Communications physics, 2021
Throughout the years, strongly correlated coherent states of excitons have been the subject of intense theoretical and experimental studies. This topic has recently boomed due to new emerging quantum materials such as van der Waals (vdW) bound atomically thin layers of transition metal dichalcogenides (TMDs). We analyze the collective properties of charged interlayer excitons observed recently in bilayer TMD heterostructures. We predict strongly correlated phases-crystal and Wigner crystal-that can be selectively realized with TMD bilayers of properly chosen electron-hole effective masses by just varying their interlayer separation distance. Our results can be used for nonlinear coherent control, charge transport and spinoptronics application development with quantum vdW heterostuctures.
Exciton-phonon interaction in crystals and quantum size structures
Journal of Physics: Conference Series, 2007
In this report, the problem of electron-phonon interaction (EPI) in bulk semiconductors and quantum dots (QDs) is considered. It is shown that the model of strong EPI developed for organic molecular crystals can be successfully applied to bulk and nanosized semiconductors. The idea of the approach proposed is to describe theoretically the experimental Raman (IR) spectra, containing the phonon replicas, by varying the EPI constant. The main parameter of the theoretical expression ( S ) is the ratio of EPI constant ( S ) to the frequency of the corresponding phonon mode ( S ). The theoretical results show that variation of the QD size can change the value of S .
npj 2D Materials and Applications, 2022
The multivalley band structure of monolayer transition metal dichalcogenides (TMDs) gives rise to intravalley and intervalley excitons. Much knowledge of these excitons has been gained, but fundamental questions remain, such as how to describe them all in a unified picture with their correlations, how are those from different valleys coupled to form the intervalley biexciton? To address the issues, we derive an exciton Hamiltonian from interpair correlations between the constituent carriers-fermions of two excitons. Identifying excitons by irreducible representations of their point symmetry group, we find their pairwise interaction depending on interacting excitons’ symmetry. It is generally repulsive, except for the case excitons from different valleys, which attract each other to form the intervalley biexciton. We establish a semianalytical relationship between the biexciton binding energy with exciton mass and dielectric characteristics of the material and surroundings. Overall, ...