Excitons in atomically thin transition-metal dichalcogenides

Chernikov, Alexey; Berkelbach, Timothy C.; Hill, Heather M.; Rigosi, Albert F.; Li, Yilei; Aslan, Özgür Burak; Hybertsen, Mark S.; Heinz, Tony F.

doi:10.1364/cleo_qels.2014.ftu2b.6

Cited by 149 publications

(256 citation statements)

References 116 publications

(174 reference statements)

Supporting

Mentioning

233

Contrasting

Order By: Relevance

“…states of the hydrogen model. The numerically exact eigenstates of the Hamiltonian (1) have been found to be in excellent agreement with measured peak positions in high-quality monolayer WS 2 samples, 45 highlighting the particular form of the screened electron-hole interaction discussed here.…”

Section: Discussionsupporting

confidence: 68%

Theory of neutral and charged excitons in monolayer transition metal dichalcogenides

2013

Self Cite

View full text Add to dashboard Cite

We present a microscopic theory of neutral excitons and charged excitons (trions) in monolayers of transition metal dichalcogenides, including molybdenum disulfide. Our theory is based on an effective mass model of excitons and trions, parametrized by ab initio calculations and incorporating a proper treatment of screening in two dimensions. The calculated exciton binding energies are in good agreement with high-level many-body computations based on the Bethe-Salpeter equation. Furthermore, our calculations for the more complex trion species compare very favorably with recent experimental measurements, and provide atomistic insight into the microscopic features which determine the trion binding energy.2

show abstract

Section: Discussionsupporting

confidence: 68%

Theory of neutral and charged excitons in monolayer transition metal dichalcogenides

2013

Self Cite

View full text Add to dashboard Cite

show abstract

“…21,22,27,[34][35][36][37][38]40 In Table I, the dielectric constants for the IL and CT exciton are denoted by κ and κ = √ κ κ ⊥ , respectively, 8,[39][40][41] where κ and κ ⊥ represent the dielectric constants parallel and perpendicular to the layer, respectively. Accordingly, by using the binding energy of the IL exciton E b, directly measured from the experiments in ML TMDs, 27,34-38 the binding energy of the CT exciton E b,⊥ and the exciton Bohr radius a B (a B⊥ ) for the IL (CT) exciton are calculated, as shown in Table I.…”

Section: Model and Formalismmentioning

confidence: 99%

“…21,22 The experimentally measured energy gap between the lowest conduction band and highest valence band, 27,[34][35][36][37][38] and energy splitting for the valence bands are also listed in Table I. 21,22,27,35,36,38 Based on the material parameters in Table I, for the BL WS 2 , the energy levels E 1 and E 2 for the IL and CT excitons are further calculated, shown in Table II. In Table II, the two kinds of excimer states in BL TMDs are further represented by |IL A ; CT B and |IL B ; CT A , respectively.…”

Section: Model and Formalismmentioning

confidence: 99%

“…Whereas in BL TMDs, the experimentally measured exciton binding energy is much larger than the inter-layer hopping energy for the hole. 21,22,27,[34][35][36][37][38] Therefore, one should first deal with the Coulomb interaction and then the effect of the inter-layer hopping of the hole to get the correct picture for the excitation in BL TMDs, as we do in this study.…”

Section: 44-46mentioning

confidence: 99%

See 1 more Smart Citation

Theory of optical excitation spectra and depolarization dynamics in bilayerWS2from the viewpoint of excimers

2014

Phys. Rev. B

View full text Add to dashboard Cite

We investigate the optical excitation spectra and the photoluminescence depolarization dynamics in bilayer WS2. A different understanding of the optical excitation spectra in the recent photoluminescence experiment by Zhu et al. [arXiv:1403.6224] in bilayer WS2 is proposed. In the experiment, four excitations (1.68, 1.93, 1.99 and 2.37 eV) are observed and identified to be indirect exciton for the Γ valley, trion, A exciton and B exciton excitations, respectively, with the redshift for the A exciton energy measured to be 30∼50 meV when the sample synthesized from monolayer to bilayer. According to our study, by considering there exist both the intra-layer and charge-transfer excitons in the bilayer WS2, with inter-layer hopping of the hole, there exists excimer state composed by the superposition of the intra-layer and charge-transfer exciton states. Accordingly, we show that the four optical excitations in the bilayer WS2 are the A charge-transfer exciton, A ′ excimer, B ′ excimer and B intra-layer exciton states, respectively, with the calculated resonance energies showing good agreement with the experiment. In our picture, the speculated indirect exciton, which involves a high-order phonon absorption/emission process, is not necessary. Furthermore, the binding energy for the excimer state is calculated to be 40 meV, providing reasonable explanation for the experimentally observed energy redshift of the A exciton. Based on the excimer states, we further derive the exchange interaction Hamiltonian. Then the photoluminescence depolarization dynamics due to the electron-hole exchange interaction is studied in the pump-probe setup by the kinetic spin Bloch equations. We find that there is always a residual photoluminescence polarization that is exactly half of the initial one, lasting for an extremely long time, which is robust against the initial energy broadening and strength of the momentum scattering. This large steady-state photoluminescence polarization indicates that the photoluminescence relaxation time is extremely long in the steady-state photoluminescence experiment, and can be the cause of the anomalously large photoluminescence polarization, nearly 100% observed in the experiment by Zhu et al. in the bilayer WS2. This steady state is shown to come from the unique form of the exchange interaction Hamiltonian, under which the density matrix evolves into the one which commutes with the exchange interaction Hamiltonian.

show abstract

“…Similarly, a positive trion is prototyped by a helium cation where one electron is bound to two protons [1]. In semiconductors, and particularly two-dimensional transition metal dichalcogenide monolayers (2D-TMDs), trions arise from charging bound electron-hole pairs (excitons) [2][3][4][5][6][7][8][9]. After their predicted existence in bulk semiconductors in the late 1950s [4], the journey for observing them took almost two decades [9].…”

Section: Introductionmentioning

confidence: 99%

Observation of two distinct negative trions in tungsten disulfide monolayers

et al. 2015

View full text Add to dashboard Cite

Ultrafast pump-probe spectroscopy of two-dimensional tungsten disulfide monolayers (2D-WS 2 ) grown on sapphire substrates revealed two transient absorption spectral peaks that are attributed to distinct negative trions at ~2.02 eV (T 1 ) and ~1.98 eV (T 2 ). The dynamics measurements indicate that trion formation by the probe is enabled by photodoped electrons remaining after trapping of holes from excitons or free electron-hole pairs at defect sites in the crystal or on the substrate. Dynamics of the characteristic absorption bands of excitons X A and X B at ~2.03 and ~2.40 eV, respectively, were separately monitored and compared to the photoinduced absorption features. Selective excitation of the lowest exciton level X A using λ pump <2.4 eV forms only trion T 1 implying that the electron remaining from dissociation of exciton X A is involved in the creation of this trion with a binding energy ~ 10 meV with respect to X A . The absorption peak corresponding to trion T 2 appears when λ pump >2.4 eV, which is just sufficient to excite exciton X B . The dynamics of trion T 2 formation are found to correlate with the disappearance of the bleach of X B exciton, indicating the involvement of holes participating in the bleach dynamics of exciton X B . Static electrical-doping photoabsorption measurements confirm the presence of an induced absorption peak similar to that of T 2 . Since the proposed trion formation process here involves exciton dissociation through hole-trapping by defects in the 2D crystal or substrate, this discovery highlights the strong role of defects in defining optical and electrical properties of 2D metal chalcogenides, which is relevant to a broad spectrum of basic science and technological applications.

show abstract

Excitons in atomically thin transition-metal dichalcogenides

Cited by 149 publications

References 116 publications

Theory of neutral and charged excitons in monolayer transition metal dichalcogenides

Theory of neutral and charged excitons in monolayer transition metal dichalcogenides

Theory of optical excitation spectra and depolarization dynamics in bilayerWS2from the viewpoint of excimers

Observation of two distinct negative trions in tungsten disulfide monolayers

Contact Info

Product

Resources

About