https://scholar.dgist.ac.kr/handle/20.500.11750/75 2026-06-04T05:57:52Z 2026-06-04T05:57:52Z Choi, Youngchan Bae, Gimin Lee, J. D. https://scholar.dgist.ac.kr/handle/20.500.11750/60357 2026-05-22T01:40:12Z 2026-02-28T15:00:00Z

Title: Pseudospin-selective polarimetric singularities in high-harmonic generation of black phosphorus Author(s): Choi, Youngchan; Bae, Gimin; Lee, J. D. Abstract: Black phosphorus (BP) exhibits net opposite pseudospin polarizations for the electron and hole states. The pseudospin structure of BP causes a selectivity in the optical excitation engaging the symmetry between the optical pump polarization and the pseudospin state, which is confirmed in a simulation of the time-resolved angle-resolved photoemission spectroscopy (tr-ARPES). Further, the pseudospin selectivity is found to drive a unique polarimetric singularity in the high-harmonic generation (HHG). Given the nth-order high-harmonic signal, we reveal that the singularity arises predominantly through the multiphoton interband pathway and thereby becomes markedly substantial at n omega pump >= Eg. omega pump is the pump photon energy and Eg the energy gap of BP. This permits a coherent understanding of the pseudospin selectivity from tr-ARPES to HHG. In particular, the pseudospin-selective polarimetric singularity suggests a potential for the pseudospintronics to be integrated into the intrinsic dynamics due to the light-matter interaction in two-dimensional materials.

2026-02-28T15:00:00Z Park, Hyosub Lee, JaeDong https://scholar.dgist.ac.kr/handle/20.500.11750/58574 2025-07-25T02:46:47Z 2025-04-30T15:00:00Z

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.

2025-04-30T15:00:00Z Katiyar, Ajit Kumar Kim, Youngjae Kim, Beom Jin Choi, Jonggyu Hoang, Anh Tuan Lee, JaeDong Ahn, Jong-Hyun https://scholar.dgist.ac.kr/handle/20.500.11750/58295 2025-07-25T02:44:50Z 2025-04-30T15:00:00Z

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.

2025-04-30T15:00:00Z 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 https://scholar.dgist.ac.kr/handle/20.500.11750/58267 2025-07-25T02:44:51Z 2025-05-31T15:00:00Z

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.

2025-05-31T15:00:00Z