Strong light–matter coupling in two-dimensional atomic crystals

Abstract

interaction that 2D materials have demonstrated has made them highly attractive for practical device applications. Graphene, the archetype 2D material was explored extensively for a wide array of photonic applications 1 . However, due to the lack of direct bandgap in graphene, considerable attention has shifted towards 2D materials known as layered transition metal dichalcogenides (TMDs) 2,3 . These TMDs are a group of naturally abundant material with a MX 2 stoichiometry, where M is a transition metal element from group VI (M = Mo, W); and X is a chalcogen (M = S, Se, Te). One of the most intriguing aspect of TMDs is the emergence of fundamentally distinct electronic and optoelectronic properties as the material transitions from bulk to the 2D limit (monolayer) [4][5][6][7][8] . For example, the TMDs evolve from indirect to direct bandgap semiconductors spanning the energy range of 1.1 to 1.9 eV in the 2D limit 4-6 .Among the TMDs, molybdenum disulphide (MoS 2 ) is one of the most widely studied systems used to demonstrate 2D light emitters 9 , transistors 10,11 , valleytronics 12-15 and photodetectors 16,17 . The novel excitonic properties of 2D MoS 2 that make it very interesting for both fundamental studies and applications include: (i) the enhanced direct band gap photoluminescence (PL) quantum yield of the monolayer compared with the bulk counterpart 7,8 , (ii) the small effective exciton Bohr radius (0.93 nm) and associated large exciton binding energy (0.897 eV) 18,19 providing the opportunity for excitonic devices that operate at room temperature (RT) and (iii) the 2D nature of the dipole orientation making the excitonic emission highly anisotropic 20 . 3The interaction of a dipole with light can be modified by altering the surrounding dielectric environment. The most widely studied and technologically relevant phenomenon in this context is the Purcell enhancement wherein the spontaneous emission rate of the dipole is enhanced using an optical cavity by altering the photon density of states. Here the coupling between the dipole and the cavity photon is defined to be in the weak coupling regime since the interaction strength is weaker than the dissipation rates of the dipole and the photon. This regime has been demonstrated in the 2D materials using photonic crystal cavities coupled to 2D layers of MoS 2 21 , and WSe 2 22 . It resulted in an enhancement of the spontaneous emission rate and highly directional photon emission.When the interaction between the dipole and the cavity photons occur at a rate that is faster than the average dissipation rates of the cavity photon and dipole, one enters the strong coupling regime resulting in the formation of new eigenstates that are half-light -half-matter bosonic quasiparticles called cavity polaritons. Since with the pioneering work of Weisbuch et al. 23 there have been numerous demonstrations of cavity polariton formation and associated exotic phenomena in solid state systems using microcavities and quantum wells that support quasi 2D excitons [24][25][26] . H...

Photo-FETs: Phototransistors Enabled by 2D and 0D Nanomaterials

“…Next to plasmonics 62 and optical cavities 69 for enhanced absorption, another very encouraging method is to sensitize a thin channel material with strongly absorbing semiconductors (sensitizers) of opposite doping polarity to The concept of sensitized high mobility materials does not only apply to 2D layered materials.…”

Exciton-plasmon coupling interactions: from principle to applications

“…The strong coupling of exciton-plasmon is achieved when the energy that transfers between the light and exciton is larger than their average dissipation, with the formation of a matter-light hybrid state and a new quasi-particle (plexciton) with distinct properties possessed by neither original particle [73]. In strong coupling regime, the new model, which has different properties of the two resonators involved (the resonators are photons and excitons, respectively, where we assume in the semiconductor resonator), results in a series of interesting phenomenon and shows great value in different areas of application [74].…”

“…Plasmons in the first 1-100 fs [73] follow landau damping. The thermal distribution of electron-hole pairs decays either through the reemission of photons or through carrier multiplication caused by electron-electron interactions [139].…”

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

“…51 Time-resolved PL and second-order correlation experiments from single emission lines will provide further insight into the nature of the discrete emitters. An open question is whether the QD like emitters inherit the valley selection rules.…”