Browsing by Author "Horng, Jason"

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Engineering radiative coupling of excitons in 2D semiconductors
(2019-11-20)
Horng, Jason
;
Chou, Yu-Hsun
;
Chang, Tsu-Chi
;
Hsu, Chu-Yuan
;
Lu, Tien-Chang
The resonance energy and the transition rate of atoms, molecules, and solids were understood as their intrinsic properties in classical electromagnetism. It was later realized that these quantities are linked to the radiative coupling between the transition dipole and photon modes. Such effects can be greatly amplified in macroscopic many-body systems from virtual photon exchange between dipoles, but are often masked by inhomogeneity and pure dephasing, especially in solids. Here, we observe in both absorption and emission spectroscopy the renormalization of the exciton resonance and the radiative decay rate in transition metal dichalcogenides monolayers due to their radiative interactions. Tuning the photon mode density near the monolayer, we demonstrate control of cooperative Lamb shift, radiative decay, and valley polarization of the excitons as well as control of the charged exciton emission. Our work establishes a technologically accessible and robust experimental system for engineering cooperative matter-light interactions. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Perfect Absorption by an Atomically Thin Crystal
(2020-08-05)
Horng, Jason
;
Martin, Eric W.
;
Chou, Yu-Hsun
;
Courtade, Emmanuel
;
Chang, Tsu-chi
Optical absorption is one of the most fundamental processes in light-matter interactions. The ability to achieve and control high absorption is crucial for a broad range of modern photonic technologies. In nanomaterials of length scales much smaller than a wavelength, optical absorption is typically a weak perturbation. To achieve high absorption, exquisite techniques and structures have been developed, such as coherent interference of multiple laser beams and plasmonic metasurfaces. Here, we show that a robust critical-coupling condition exists to allow perfect absorption of light by a subnanometer-thick two-dimensional semiconductor, when the radiative-decay rate of the exciton resonance balances with its loss rate. We measure an absorption up to 99.6% in a monomolecular MoSe2 crystal placed in front of a flat mirror. We furthermore demonstrate control of the perfect absorption by tuning the exciton-phonon, exciton-exciton, and exciton-photon interactions with temperature, pulsed laser excitation, and a movable mirror, respectively. Our work suggests a mechanism to achieve and control critical coupling in two-dimensional excitonic systems, enabling photonic applications including ultrafast low-power light modulators and sensitive optical sensing.