https://scholar.dgist.ac.kr/handle/20.500.11750/75 Sat, 04 Apr 2026 12:46:21 GMT 2026-04-04T12:46:21Z https://scholar.dgist.ac.kr/handle/20.500.11750/58574 Title: Floquet engineering of excitons in monolayer MoS2 Author(s): Park, Hyosub; Lee, JaeDong Abstract: Floquet dynamics temporally deforms the band structure of the system, called Floquet engineering, under a strong optical field. Although a single resonant pulse simultaneously drives both exciton and Floquet dynamics, the Floquet engineering during exciton generation remains unexplored. We examine the Floquet engineering of excitons by a theoretical simulation of the time-resolved and angle-resolved photoemission spectroscopy in monolayer MoS2. Our finding reveals that the exciton experiences nontrivial engineering inducing a distinct asymmetry in the development of spectral splitting with the time delay and pump intensity, which are underlain by the electron-hole interaction inherent in the exciton binding. © 2025 American Physical Society. Wed, 30 Apr 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58574 2025-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58295 Title: Strain-Induced Bandgap Narrowing in Crumpled TMDs for NIR Light Detection Author(s): Katiyar, Ajit Kumar; Kim, Youngjae; Kim, Beom Jin; Choi, Jonggyu; Hoang, Anh Tuan; Lee, JaeDong; Ahn, Jong-Hyun Abstract: Transition metal dichalcogenides (TMDs) such as MoS2 and WS2 emerge as promising materials in optoelectronics, especially for flexible photo- /image-sensors due to their direct bandgap nature. However, the intrinsic bandgaps of these semiconductor monolayers (e.g., MoS2 ≈1.86 eV and WS2 ≈2.0 eV) restrict the operational wavelength range of developed photosensors in the visible spectrum. In addition, their ultrathin nature provides a limited optical absorption cross-section that restricts the device's performance. Exploiting the strong impact of strain on the electronic band structure, strain engineering has emerged as a promising approach for adjusting the electrical and optical characteristics of layered semiconductors. In particular, the application of tensile strain in MoS2 and WS2 can decrease their bandgaps, which potentially can extend the optical absorption toward the near-infrared (NIR) wavelength. Herein, a non-conventional crumpling approach is employed to incorporate uniaxial tensile strain into a graphene/TMD/graphene metal-semiconductor-metal photodetector (PD) array. The utilized crumpled geometry provides exclusive photon management with enhanced light scattering and trapping at the sinusoidal surface that results in increased light absorption in NIR wavelength range. © 2025 Wiley-VCH GmbH. Wed, 30 Apr 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58295 2025-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58267 Title: Wafer-scale AA-stacked hexagonal boron nitride grown on a GaN substrate Author(s): Moon, Seokho; Okello, Odongo Francis Ngome; Rousseau, Adrien; Choi, Chang-Won; Kim, Youngjae; Park, Yunjae; Kim, Jiye; Kim, Jaewon; Kim, Minhyuk; Valvin, Pierre; Cho, Jaehee; Watanabe, Kenji; Taniguchi, Takashi; Jeong, Hu Young; Fugallo, Giorgia; Desrat, Wilfried; Ding, Feng; Lee, JaeDong; Gil, Bernard; Cassabois, Guillaume; Choi, Si-Young; Kim, Jong Kyu Abstract: The stacking sequence of two-dimensional hexagonal boron nitride (hBN) is a critical factor that determines its polytypes and its distinct physical properties. Although most hBN layers adopt the thermodynamically stable AA ' stacking sequence, achieving alternative stacking configurations has remained a long-standing challenge. Here we demonstrate the scalable synthesis of hBN featuring unprecedented AA stacking, where atomic monolayers align along the c axis without any translation or rotation. This previously considered thermodynamically unfavourable hBN polytype is achieved through epitaxial growth on a two-inch single-crystalline gallium nitride wafer, using a metal-organic chemical vapour deposition technique. Comprehensive structural and optical characterizations, complemented by theoretical modelling, evidence the formation of AA-stacked multilayer hBN and reveal that hBN nucleation on the vicinal gallium nitride surface drives the unidirectional alignment of layers. Here electron doping plays a central role in stabilizing the AA stacking configuration. Our findings provide further insights into the scalable synthesis of engineered hBN polytypes, characterized by unique properties such as large optical nonlinearity. Sat, 31 May 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58267 2025-05-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58210 Title: Tunable Polariton Rabi Oscillation in Phase-Changing Perovskite Microcavities Author(s): Choi, Hyeon-Seo; Ko, Minjee; Lee, Taejin; Jung, Jin-Woo; Lee, Young-Jun; Jeong, Hyeonjong; Kim, Youngjae; Kim, Dongha; Heo, Jinhee; Lee, Shinbuhm; Lee, JaeDong; Cho, Chang-Hee Abstract: Exciton-polaritons are composite quasiparticles hybridized between excitons and photons, which are very promising to develop quantum information devices such as entangled photon pair sources and polariton qubit devices by utilizing the fascinating properties of strong nonlinearity, Bose-Einstein condensation, and superfluidity. Organic-inorganic hybrid lead halide perovskites have attracted much interest in cavity quantum electrodynamics due to their excellent excitonic properties, including strong exciton binding energy and high oscillation strength. Here, tunable Rabi oscillation of exciton-polaritons in the lead halide perovskite microcavity is demonstrated, which experiences a phase transition between orthorhombic, tetragonal, and cubic phases by varying the temperature. Over the phase transition, the Rabi frequency is probed by tracing the dispersion relation of the exciton-polaritons using Fourier plane spectroscopy. Due to the emergence of ferroelectricity in the tetragonal phase of the perovskites, the Rabi splitting can be tuned by approximate to 20%, while the corresponding exciton oscillator strength is varied by approximate to 44%. These results provide insight into novel functionalities of polariton devices by utilizing ferroic semiconductors, which can facilitate the development of tunable quantum devices. Wed, 30 Apr 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/58210 2025-04-30T15:00:00Z