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Bo Han, Jamie M. Fitzgerald, Lukas Lackner, Roberto Rosati, Martin Esmann, Falk Eilenberger, [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), Marcin Syperek, Ermin Malic, Christian Schneider

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[Infrared Magnetopolaritons in <math display="inline">  <mrow>    <msub>      <mrow>        <mi>MoTe</mi>      </mrow>      <mrow>        <mn>2</mn>      </mrow>    </msub>  </mrow></math> Monolayers and Bilayers](https://mdr.nims.go.jp/datasets/a15fbd59-df3b-4674-8991-05ecc6a3744a)

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Infrared Magnetopolaritons in MoTe2 Monolayers and BilayersInfrared Magnetopolaritons in MoTe2 Monolayers and BilayersBo Han ,1 Jamie M. Fitzgerald ,2 Lukas Lackner ,1 Roberto Rosati,2 Martin Esmann ,1 Falk Eilenberger ,3,4,5Takashi Taniguchi ,6 Kenji Watanabe ,7 Marcin Syperek,8 Ermin Malic ,2 and Christian Schneider1,*1Institut für Physik, Fakultät V, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany2Department of Physics, Philipps-Universität Marburg, Mainzer Gasse 33, D-35032 Marburg, Germany3Fraunhofer-Institute for Applied Optics and Precision Engineering IOF, 07745 Jena, Germany4Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller Universität Jena, 07745 Jena, Germany5Max Planck School of Photonics, 07745 Jena, Germany6International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan7Research Center for Functional Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan8Department of Experimental Physics, Faculty of Fundamental Problems of Technology,Wrocław University of Science and Technology, Wyb.Wyspiańskiego 27, 50-370 Wrocław, Poland(Received 17 July 2024; revised 6 December 2024; accepted 14 January 2025; published 20 February 2025)MoTe2 monolayers and bilayers are unique within the family of van der Waals materials since they pavethe way toward atomically thin infrared light-matter quantum interfaces, potentially reaching the importanttelecommunication windows. Here, we report emergent exciton polaritons based on MoTe2 monolayersand bilayers in a low-temperature open microcavity in a joint experiment-theory study. Our experimentsclearly evidence both the enhanced oscillator strength and enhanced luminescence of MoTe2 bilayers,signified by a 38% increase of the Rabi splitting and a strongly enhanced relaxation of polaritons to low-energy states. The latter is distinct from polaritons in MoTe2 monolayers, which feature a bottlenecklikerelaxation inhibition. Both the polaritonic spin valley locking in monolayers and the spin-layer locking inbilayers are revealed via the Zeeman effect, which we map and control via the light-matter composition ofour polaritonic resonances.DOI: 10.1103/PhysRevLett.134.076902Introduction—Two-dimensional semiconductors oftransition metal dichalcogenides (TMDCs) are an excellentresearch platform for solid-state cavity quantum electro-dynamics due to their strong light-matter interactions andintriguing spin-valley locking [1–3]. Their optical proper-ties hinge on very robust valley excitons with bindingenergies of hundreds of meV [4–6]. Composite quasipar-ticles such as exciton polaritons in TMDC microcavitysystems can inherit physical properties from both the cavitymodes and the optically active material, including theultralight effective mass [7], magnetic responses [8,9],and nonlinearities due to exchange correlation [10,11],dipolar interaction [12], phase space filling [13], and moiréconfinement [14]. Therefore, they are remarkable systemsto explore collective phenomena such as bosonic conden-sation [15,16], coherent light emission [17–20], polaritonblockade [21,22], and correlated magnetism [23].Among the TMDC family members, MoTe2 features aunique band structure with both the monolayer (ML) andbilayer (BL) exhibiting a direct band gap [24–29].The ground-state excitonic resonances lie in the nearinfrared spectral range ∼1.1 μm [29,30], making MoTe2a good candidate for optoelectronic [31] and quantumoptical applications [32] in the optical telecommunicationwindow [33]. The extraordinary electronic properties[34,35] also render MoTe2 a promising material for studiesof integer and fractional (anomalous) (spin) quantum Halleffects [36–39]. However, the strong light-matter couplingregime of MoTe2 has not received notable attention.In this Letter, we demonstrate the first experimentalmeasurements on the strong coupling of excitons in MoTe2ML and BL with discretized cavity modes in a low-temperature open optical microcavity. Our Letter revealsthat the BL features an increase in Rabi splitting andcoupling strength by 38% compared to the ML, whilemaintaining otherwise identical conditions. Interestingly,we observe a bottlenecklike inhibition of relaxation inML structures, effectively enhancing the luminescencefrom the upper polariton branch (UPB), while, in starkcontrast, the majority of the population relaxes to the lowerpolariton branch (LPB) in the BL. Our experiments arecomplemented by a many-particle theory revealing the*Contact author: christian.schneider@uni-oldenburg.dePublished by the American Physical Society under the terms ofthe Creative Commons Attribution 4.0 International license.Further distribution of this work must maintain attribution tothe author(s) and the published article’s title, journal citation,and DOI.PHYSICAL REVIEW LETTERS 134, 076902 (2025)Editors' Suggestion0031-9007=25=134(7)=076902(7) 076902-1 Published by the American Physical Societyhttps://orcid.org/0000-0002-6562-6333https://orcid.org/0000-0003-3652-0676https://orcid.org/0000-0002-7970-0450https://orcid.org/0000-0002-2329-9696https://orcid.org/0000-0002-4646-2484https://orcid.org/0000-0002-1467-3105https://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0003-1434-9003https://ror.org/033n9gh91https://ror.org/01rdrb571https://ror.org/02afjh072https://ror.org/05qpz1x62https://ror.org/026v1ze26https://ror.org/026v1ze26https://ror.org/008fyn775https://crossmark.crossref.org/dialog/?doi=10.1103/PhysRevLett.134.076902&domain=pdf&date_stamp=2025-02-20https://doi.org/10.1103/PhysRevLett.134.076902https://doi.org/10.1103/PhysRevLett.134.076902https://doi.org/10.1103/PhysRevLett.134.076902https://doi.org/10.1103/PhysRevLett.134.076902https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/microscopic mechanisms behind this qualitatively differentbehaviour in MoTe2 ML and BL. Using systematicmagneto-optics measurements, we explore the polaritonicZeeman effect and reveal g-factors controlled by the cavity-exciton detuning, manifesting the valley and layer degreesof freedom in the ML and BL, respectively. We alsodiscover an unconventional enhancement of the couplingstrength of both the ML and BL in the magnetic field.Strong Coupling and Quasiparticle Relaxation—TheMoTe2 ML and BL are encapsulated [40] with thinhexagonal boron nitride flakes and deposited on a distrib-uted Bragg reflector (DBR) with a stop band centered at1050 nm, see Figs. S1(a), S1(b), and S1(e) of theSupplemental Material [41]. The samples are loaded in aclosed-cycle low-temperature cryostat (3.5 K) equippedwith a superconducting magnet. First, we perform thephotoluminescence (PL) and differential reflectivity (DR)measurements on the encapsulatedMoTe2 flakes by using alinearly polarized 765 nm continuous wave laser and atungsten-halogen lamp, respectively. The indiscernibleStokes shift between the PL and DR proves the highquality of our samples [see Figs. S1(f–i) [41] ]. Moreexperimental details are summarized in Section III of [41].For strong coupling measurements, we use a top mirrorthat is a gold-coated silica mesa with a premanufacturedspherical-cap shaped lens structure of 6 μm diameter and300 nm depth [see Figs. S1(c) and S1(d) [41] ]. A schematicof the cavity setting is shown in Fig. 1(a). The lens andbottom DBR form discretized Tamm-plasmon lens modes(Q factors ∼400) that can be readily measured in PL or DR.The focused excitation spots are comparable to thelens diameter. Our previous works have demonstratedthe capability of discretized Tamm modes in tuning theemitters’ spontaneous emission rates in the weak couplingregime [57,58]. A DC voltage applied to the actuator canchange the cavity length with sub-nm positioning resolu-tion. The PL and DR measurements are thus performedwith a fine detuning step size of 0.1 meV. The detuningΔ ¼ EC − EX is defined as the energetic differencebetween the cavity and exciton modes. Both measuredML and BL samples are deliberately tuned to couple withthe eighth longitudinal lens mode, corresponding to acavity length of approximately 4.28 μm at Δ ¼ 0.In cavity-length dependent DRmeasurements in Figs. 1(b)and 1(c), we observe clear anticrossing features. We applycoupled oscillators theory to calculate the energy ofboth polariton branches as a function of the cavity-excitondetuning via EUPBðLPBÞ ¼ ðEXþEC�ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiV2þΔ2pÞ=2, whereV is the coupling strength. The fitting of polariton resonancesin ML and BL are superimposed on the experimental DRresults in Figs. 1(b) and 1(c), as well as in the PL measure-ments in Figs. 2(a) and 2(b). This approach yields a couplingstrength of V0TML ¼ 13 meV for the MoTe2 ML (position 1)and V0TBL ¼ 18 meV for the BL. The superscript 0 Tindicates the absence of an external magnetic field. Weencounter a slight variation of the coupling strength fordifferent sample positions of the ML on the order of thepolariton linewidth (see Figs. S5 and S6 for measurementson different positions: P2 and P3 [41]). Indeed, theobserved increase of the Rabi splitting by a factor of1.38 for the BL is in agreement with the Tavis-Cummingsmodel, which predicts a scaling with the square root of thenumber of oscillators [59–61].A striking difference between ML and BL polaritonsbecomes apparent when comparing the PL intensitybetween the UPB and LPB in the two cases. Figure 2(a)depicts the PL from the polaritonic modes for the MLsample (P1), whereas the BL case is plotted in Fig. 2(b)with identical excitation conditions. For BL polaritons, theUPB emission is much weaker than the emission from theLPB, which is indicative of efficient relaxation of pop-ulation to the energetically lower state. In stark contrast,for ML polaritons, the UPB is generally more intense thanthe LPB (see Fig. S5(a) and Fig. S6(a) for other samplepositions [41]). We plot the emission intensity ratiobetween the UPB and LPB in Fig. 2(e) to quantify therelaxation strength for all detunings: in the BL case, theintensity ratio is generally smaller than 0.4, which isindicative of enhanced PL from the LPB, as a consequenceof efficient relaxation. However, in the case of the ML, theratio exceeds unity even for very red detuning and increasesdramatically toward the zero and blue detuning regimes.We model the polariton population and relaxation inour systems using a material-realistic many-particle−20 −10 0 10 201.151.161.171.181.19Detuning (meV)Energy (eV)cavityXML(P1)(b)VML=13 meV−20 −10 0 10 201.131.141.151.16−0.3−0.2−0.10Detuning (meV)Energy (eV)cavityXBL(c)V =18 meV(a)mesagoldMoTeDBRUPBLPBUPBLPBFIG. 1. (a) Schematic of the open cavity embedded with MoTe2MLandBL in amagnetic field. The valley Zeeman effect for layerswith inversion symmetry is sketched in the right panel. (b) DR as afunction of cavity detuning with a cavity loaded with a ML (P1),featuring exciton energyEMLX ¼ 1.1719 eV and a Rabi splitting ofV0TML ¼ 13 meV. (c) DR in BL as a function of cavity detuning,featuring EBLX ¼ 1.1513 eV and V0TBL ¼ 18 meV. Detuning ismodified with a change of cavity length. The color bar is identicalfor (b) and (c).PHYSICAL REVIEW LETTERS 134, 076902 (2025)076902-2theory [41]. Exciton polaritons are modeled within aWannier-Hopfield framework [62], using the experimen-tally extracted light-matter coupling parameters and a barecavity linewidth of 1.5 meV. Polariton-phonon scattering isdescribed via the deformation potential and second-orderBorn-Markov approximation [63,64]. In particular, weexplicitly account for the A1 homopolar phonon with anenergy of 21 meV, which strongly interacts with excitons inMoTe2 [30,65]. The values for the deformation potentialsare extracted from experimentally measured temperature-dependent linewidths of the 1s exciton in both ML and BLMoTe2 (see Fig. S7 [41]). We find an increased exciton-phonon coupling for the BL, in agreement with previousstudies [26]. The frequency-dependent PL at steady-stateconditions is given by the polariton Elliot formula [63]IðωÞ ¼Xn¼LPB;UPBγnΓnðEn − ℏωÞ2 þ ðγn þ ΓnÞ2N0n; ð1Þwhere γ and Γ are the polariton radiative and phonon-induced decay rates, respectively; En is the polaritonenergy; and N0n is the Boltzmann distribution of the quasiparticles. We fix the effective temperature of the exciton gasto 60 K to consider the realistic case of imperfect thermal-ization. The results of the model are plotted for the case ofML [Fig. 2(c)] and BL polaritons [Fig. 2(d)]. Strikingly, thedramatic increase of the lower polariton PL for the BL iswell captured in our microscopic description, which veri-fies the impact of the A1 phonon mode on the relaxationdynamics. The more efficient polariton relaxation observedfor the BL is attributed to the combined effect of theenhanced exciton-phonon coupling and larger Rabi split-ting. The BL polariton has a larger excitonic character atthe negative detunings where the scattering channel fromthe exciton reservoir opens up [see Fig. 2(f)], i.e.,ELPB þ EA1≈ EX, where EA1is the A1 phonon energy.This, together with the larger exciton-phonon scattering inthe BL, leads to a significantly larger occupation of the BLLPB at all detunings.Polaritonic magneto optics—Polaritons are light-matterhybrid quasiparticles whose magnetic responses stem fromtheir specific excitonic nature. The polaritonic g factor−20 −10 0 10 201.151.161.171.181.19Detuning (meV)Energy (eV)cavityX(a) ML(P1)VML=13 meV−20 −10 0 10 201.131.141.151.1601000Detuning (meV)Energy (eV)cavityXBL(b)counts/30 sVBL=18 meV−20 −10 0 10 201.151.161.171.181.19Detuning (meV)Energy (eV)cavityX(c) ML (sim.)VML=13 meVUPBLPB−20 −10 0 10 201.131.141.151.1600.51Detuning (meV)Energy (eV)cavityX(d) BL (sim.)VBL=18 meVUPBLPB−10 −5 0 50123Detuning (meV)I UPB/ILPBML (P1)BL(e)LPB LPBUPB UPB10−5 10−4 10−3 0.01 0.1 11.131.141.151.16Wavevector (nm-1)Energy (eV)(f)UPBLPBBL-Xlight coneK-K reservoircavityLPBBL-Xlight coneFIG. 2. PL spectra of exciton polaritons in (a) ML (P1) and (b) BL as a function of detuning. The ML polaritons feature a significant PLemission from the UPB, whereas BL polaritons exhibit substantial particle relaxation into the LPB. Note that the oscillatory intensity of thepolariton branches is caused by detector etalon effects (see Fig. S3 of [41] for more details). Polariton energies extracted from the DRspectra using the coupled oscillator model are superimposed on the PL anticrossings, demonstrating excellent consistency. Theoreticaldescription of the PL for (c) MoTe2 ML and (d) BL polaritons, based on the material-realistic parameters from the experiments. Bothabsolute intensities are normalized to the BL emission, sharing the same color bar of (d). (e) Experimentally extracted PL intensity ratiobetween the UPB and LPB in MoTe2 ML and BL as a function of the detuning. (f) Schematic of the polariton relaxation regime. Thedetuning is set to−17.5 meV to position the LPB (k ¼ 0) 21 meV below the BL exciton, matching the energy of the homopolar A1 opticalphonons. The coupling strength and exciton energy at k ¼ 0 are experimental values. The opening of relaxation to the LPB (k ¼ 0) ismarked by the blue dashed arrow.PHYSICAL REVIEW LETTERS 134, 076902 (2025)076902-3thus needs to be rescaled by the excitonic Hopfieldcoefficient: jXkj2 ¼ ðffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiΔ2k þ V2qþ ΔkÞ=2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiΔ2k þ V2q, aparameter characterizing the excitonic proportion in thepolariton. However, the polaritonic Zeeman phenomena inTMDCs have not been systematically studied with differentlight-matter compositions.Due to time-reversal symmetry, the spin, orbital, andvalley indices in the ML take opposite signs betweenadjacent K valleys, leading to a locking of spin and valleydegrees of freedom in bands with strong spin-orbit coupling.In contrast, the BL retains the inversion symmetry, whichleads to the intriguing phenomenon of spin-layer locking[66–68]. Both phenomena reveal distinctive spectral signa-tures in polarization spectroscopy in the presence of externalmagnetic fields, as sketched in Fig. 1(a). To extract theexciton out-of-plane g factor, magneto-DR measurementsare performed between �9 T in a Faraday geometry in theabsence of the top mirror, ensuring weak coupling condi-tions. We utilize linearly polarized excitation, and measurecounter-circularly polarized signals (σ�). The results areshown in Fig. S4 [41]. The out-of-plane excitonic g factors(gx) are calculated by fitting the Zeeman splitting of thevalley excitons by usingΔE ¼ gxμBB, where μB is the Bohrmagneton and B is the magnetic flux density. The values ofgMLX ¼ −4.6 and gBLX ¼ −4.1 are in excellent agreementwithprevious reports [69–71].We notice that the modified sample position (P3) whichis chosen for the magneto-optical study of the ML polar-itons features a slightly larger coupling strength of 16 meVmeasured at zero field [see Fig. S3(a) and Figs. S5(a) andS5(b) [41] ], which we attribute to locally varying dielectricscreening and charging effects in the ML. PolaritonicZeeman effects in both the MoTe2 ML and BL are thenextracted from magneto-PL measurements (Fig. 3).We utilize the same polarization configuration for thepolaritonic magneto-optics measurements. The polaritonicZeeman splitting as a function of the detuning is thenstraightforwardly calculated via the energetic differencesbetween σþ and σ− resonances at þ9 T.We first plot the spectrally resolved detuning-dependentpolarization patterns for ML and BL polaritons in Figs. 3(a)and 3(b), which are obtained by subtracting theσ− polarized spectrum from the σþ polarized spectrumat the same cavity detuning. The same effects are alsorevealed in the color-coded magneto-DR difference spectrathat are compiled in Figs. S5(d) and S5(f) [41]. We canimmediately see the detuning-dependent dichroism, which−20 −10 0 10 201.151.161.171.181.19−5000500Detuning (meV)Energy (eV)counts/60 s(a) ML(P3) UPBLPB−20 −10 0 10 201.131.141.151.16−10010Detuning (meV)Energy (eV)counts/60 s(b) BL UPBLPB1.15 1.16 1.17 1.18 1.1905001000Energy (eV)PL Intensity (a.u.)(c) ML(P3)+ - (meV)          +5            0           -5UPBLPBV+9T=17.5 meV1.13 1.14 1.15 1.16 1.17010002000Energy (eV)PL Intensity (a.u.)(d) BL+ - (meV)          +5            0           -5UPBLPBV+9T=19.5 meV−20 −10 0 10 20−4−3−2−10Detuning (meV)Polariton g-factors(e) ML(P3)−20 −10 0 10 20−4−3−2−10Detuning (meV)Polariton g-factors(f) BLEq.(2) Eq.(2)UPBLPBUPBLPBMLBLEq.(2) Eq.(2)FIG. 3. Polariton Zeeman effect in spectrally and polarization-resolved PL measurements at þ9 T. The color-coded Zeeman plots in(a) ML (P3) and (b) BL are obtained by subtracting the σ− polarized spectrum from the σþ polarized spectrum at the same cavitydetuning. The high polarizaton of LPB around Δ ¼ −10 meV is due to trion states that couple to the exciton polaritons via the cavityresonance (see discussion in Section III of [41]). (c) ML (P3) and (d) BL representative PL spectra of polariton Zeeman splits at Δ ¼ 0and �5 meV, corresponding to the dashed lines in (a) and (b). The Rabi splittings are Vþ9TML ¼ 17.5 meV for the ML and Vþ9TBL ¼19.5 meV for the BL. Experimental (dots) and theoretical (dashed lines) polariton g-factors in (e) ML (P3) and (f) BL. The error bars arederived by summing up the energetic error bars of the fitted polariton peaks in Figs. S5(c) and S5(e) [41].PHYSICAL REVIEW LETTERS 134, 076902 (2025)076902-4becomes especially prominent in the excitonic regime ofthe polariton branches, for example, at Δ ¼ �20 meVfor the LPB and UPB, respectively. Magneto-PL and DRdifference spectra from another sample position (P2) of theML, which display the same polaritonic Zeeman effects,are presented in Fig. S6 [41].The PL spectra at detunings of 0 and �5 meV are alsoshown in Fig. 3(c) for the ML case and Fig. 3(d) for the BLcase. The Zeeman splitting becomes very apparent in thisrepresentation and acquires a similar magnitude for the MLand BL polaritons for comparable detunings. From thedetuning-dependent Zeeman effect, we can model the UPBand LPB g factors as a function of detuning asgUPBðLPBÞ ¼gx2�ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiV2 þ Δ21p2μBB∓ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiV2 þ Δ22p2μBB; ð2Þwhere Δ1 ¼ EC − EσþX and Δ2 ¼ EC − Eσ−X are the actualcavity detunings with respect to each excitonic Zeemansplit, and Δ ¼ ðΔ1 þ Δ2Þ=2. The zero detunings of Δ1 andΔ2 are marked by double-sided arrows in Figs. S5(c) andS5(e) [41] that present the Lorentzian fitting results ofthe polariton Zeeman splits in ML and BL at þ9 T. Theexperimentally extracted polaritonic g factors of eachbranch in the ML [Fig. 3(e)] and BL [Fig. 3(f)] are inexcellent agreement with our theoretically derived valuesfrom Eq. (2). The degeneracy of the valley as well as thelayer-locked polaritons in the ML and BL is thus lifted,while the strong coupling effect is verified as a viable toolto tune the resulting optical dichroism.It is furthermore worth noting that, comparing thecoupling strength at þ9 T [Figs. 3(c) and 3(d)] tothe scenario without the magnetic field (Figs. S3(b) andS3(h) [41]), the Rabi splittings are enhanced by 1.5 meVfor both the ML and BL, corresponding to an effectiveenhancement of the coupling strength by approximately8–9%. This behavior occurs consistently for various samplepositions [see Figs. S6(e) and S6(f) [41] ]. The couplingstrength enhancement by magnetic field was previouslyreported for polaritons in III–V semiconductor quantumwells embedded in monolithic cavities [72], where themagnetic compression of exciton wave function increasesthe exciton oscillator strength and consequently enhancesthe vacuum-field Rabi splitting [73]. Our observation isthus very unconventional, since the exciton Bohr radius(aB ∼ 1–2 nm) is significantly smaller than the estimatedmagnetic length LB ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiℏ=ðe · BÞp≈ 8.6 nm.Conclusions—We report the first optical microscopymeasurements on the emergence of exciton polaritons inMoTe2 monolayer and bilayer. In contrast to the bilayerthat exhibits an efficient population relaxation to the lowerpolariton branch, the relaxation in the monolayer featuresa pronounced bottleneck phenomenon, which has beenmodeled using a microscopic many-particle theory describ-ing the scattering of exciton polaritons with A1 opticalphonons. We have also verified the strong couplings viamagneto-optics measurements, where the polariton valleyand layer degeneracies are lifted in the monolayer andbilayer, respectively. We can thus extract the polaritonic gfactors as a function of the cavity-exciton detuning. OurLetter paves the way for further research involving cavity-mediated phenomena in MoTe2-based van der Waalsheterostructures, including the study of correlated phenom-ena, Telluride-based dipolaritons, and polariton lasersoperated at telecommunication wavelengths.Acknowledgments—The project is funded by DeutscheForschungsgemeinschaft (DFG) Lantern project (fundingnumbers: Schn1376 11.1). C. S. acknowledges DFG withinthe initiative for major equipment (Project INST184-220).B. H. acknowledges Alexander von Humboldt-Stiftung fora fellowship grant. M. E. acknowledges funding fromthe Carl von Ossietzky Universität Oldenburg through aCarl von Ossietzky Young Researchers’ Fellowship. F. E.acknowledges support by DFG SFB 1375 (NOA) andBMBF FKZs 16KISQ087K and 13XP5053A. J. F, R. R.,and E. M. acknowledge funding from DFG via SFB 1083and the regular project 524612380. K.W. and T. T.acknowledge support from the JSPS KAKENHI (GrantNo. 21H05233 and 23H02052) and World PremierInternational Research Center Initiative (WPI), MEXT,Japan. M. S. acknowledges funding from ProjectNo. 2019/35/B/ST5/04308 financed by the PolishNational Science Center (NCN).[1] G. Wang, A. Chernikov, M. M. Glazov, T. F. Heinz, X.Marie, T. Amand, and B. Urbaszek, Rev. Mod. Phys. 90,021001 (2018).[2] C. Schneider, M.M. Glazov, T. Korn, S. Höfling, and B.Urbaszek, Nat. Commun. 9, 2695 (2018).[3] T. Mueller and E. Malic, npj 2D Mater. Appl. 2, 29 (2018).[4] K. F. Mak, C. Lee, J. Hone, J. Shan, and T. F. Heinz, Phys.Rev. Lett. 105, 136805 (2010).[5] A. Chernikov, T. C. Berkelbach, H. M. Hill, A. Rigosi, Y. Li,B. Aslan, D. R. Reichman, M. S. Hybertsen, and T. F. Heinz,Phys. Rev. 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