Strong coupling between excitons in transition metal dichalcogenides and optical bound states in the continuum

Abstract

Being motivated by recent achievements in the rapidly developing fields of optical bound states in the continuum (BICs) and excitons in monolayers of transition metal dichalcogenides, we analyze strong coupling between BICs in Ta2O5 periodic photonic structures and excitons in WSe2 monolayers. We demonstrate that giant radiative lifetime of BICs allow to engineer the exciton-polariton lifetime enhancing it three orders of magnitude compared to a bare exciton. We show that maximal lifetime of hybrid light-matter state can be achieved at any point of k-space by shaping the geometry of the photonic structure. Our findings open new route for the realization of the moving exciton-polariton condensates with non-resonant pump and without the Bragg mirrors which is of paramount importance for polaritonic devices.Monolayers of transition metal dichalcogenides (TMDCs) are a certain class of post-graphene two-dimensional materials [1], attracting vast research interest in recent years. TMDC are direct-gap semiconductors, exhibiting strong light-matter coupling [2]. Moreover, these structures support excitons characterized by both large binding energies and sufficiently large Bohr radii [3]. While the former leads to the existence of strong excitonic response at room temperature, the latter provides strong optical nonlinearity due to the exciton-exciton interactions [4]. Another important property of the TMDC excitons is the large oscillator strength leading to the substantial exciton-photon interaction in these structures. These properties allow the observation of the so-called strong coupling regime, leading to the emergence of the new quasiparticles, exciton-polaritons [5] at room temperatures in structures comprising TMDC monolayer and an optical cavity.Excitons-polaritons have been extensively studied in last two decades both due to their fascinating fundamental properties, such as high-temperature Bose condensation and superfluidity [6,7] as well as well as emerging applications such as virtually thresholdless polariton lasers [8] and energy effective all optical logic gates [9]. Strong coupling of TMDC excitons to light has been observed in the structures resembling the conventional microcavities, where the monolayer was sandwiched between two Bragg mirrors [10][11][12][13]. At the same time, since fabrication of high quality TMDC monolayers is based on the mechanical exfoliation techniques, and thus not compatible with the standard epitaxial techniques used for the Bragg mirror fabrication, the realization of the structures considered in [10-13] is quite technologically demanding. It would be thus extremely useful to realize high quality optical resonances without the requirement for the growth of the upper mirror. As an alternative, a whispering gallery mode (WGM) in a disc resonator could be used for the realization of the strong coupling [14]. However, this approach also requires sophisticated fabrication techniques and the precise positioning of the monolayer over the region of the disc resonator where the WGM mo...

Nonlinear polaritons in a monolayer semiconductor coupled to optical bound states in the continuum

“…17 Coupling TMD excitons to optical BICs in photonic crystals thus will not only boost the potentially achievable nonlinearities but also provide control on the resonant BIC properties through the excitonic fraction in the polariton, as has been proposed theoretically. 18 Here we experimentally demonstrate and investigate polaritons formed via strong coupling of excitons in monolayer MoSe 2 and optical BIC in a 1D photonic crystal slab, with Rabi splitting of > 27 meV and BIC-like radiation suppression in surface-normal direction.…”

“…1d, with an optical BIC state formed on the antisymmetric mode at Γ point. 18 We measure the PCS band structure via angle-resolved reflectance spectroscopy in a back focal plane setup with a slit spectrometer coupled to a liquid nitrogen cooled imaging CCD camera (Princeton Instruments), using white light from a halogen lamp for illumination (see Supplement for details). Fig.…”

Ridge Resonance in Silicon Photonics Harnessing Bound States in the Continuum

“…Due to the single resonance over a broad wavelength range, this shift can be unambiguously detected unlike other types of resonators that exhibits multiple resonances with small free spectral ranges, resulting in increasing sensing dynamic range. Strong evanescent field is also attractive for strong light–matter coupling and nonlinear optic interaction in BIC's …”

Polarization-based branch selection of bound states in the continuum in dielectric waveguide modes anti-crossed by a metal grating

“…In this case, a mode anti-crossing occurs, and the BIC appears on one of the two split-branches. Such a type of BIC is reported in cylindrical resonator system [37][38][39] and the periodic structures such as photonic [12,28,29,31] or plasmonic structures [33]. As is pointed out by Friedrich and Wintgen [40], the regime where the Q factor is kept high around the BIC becomes larger as the near-field coupling becomes stronger.…”