Quek Su Ying

@article{ISI:001466592300001,
title = {Defect Engineering in Hexagonal Boron Nitride: Optical Properties of Stable Defect Complexes Arising from Boron Interstitials},
author = {Nicholas Lin Quan Cheng and Kanchan Ajit Ulman and Su Ying Quek},
doi = {10.1021/acsami.4c19034},
times_cited = {0},
issn = {1944-8244},
year = {2025},
date = {2025-04-14},
journal = {ACS APPLIED MATERIALS & INTERFACES},
volume = {17},
number = {16},
pages = {24058-24070},
publisher = {AMER CHEMICAL SOC},
address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA},
abstract = {Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor that is promising as a host material for solid-state quantum technologies through defect engineering. It has been shown that boron atoms can be removed from the lattice upon irradiation by electrons or light ions, creating boron vacancies and boron interstitials. While the optical properties of boron-vacancy-derived defects have been studied extensively, little is known about the optical properties of boron-interstitial-derived defects. In this work, we use state-of-the-art first-principles calculations to predict the electronic and optical properties of boron interstitials (Bint) and defect complexes comprising Bint and substitutional carbon impurities at boron and nitrogen sites (CB and CN). These carbon impurities can be present in as-grown hBN and can also be introduced intentionally. We demonstrate that these complexes are expected to be stable at room temperature. Our GW-Bethe-Salpeter equation (BSE) calculations show that Bint-CB and Bint-CN have low-energy optical transitions that are isolated in energy, making them suitable as single-photon emitters. Together with constrained density functional theory calculations to capture the red shift due to emission, we predict that Bint-CB and Bint-CN have zero phonon lines at similar to 2.0 eV and similar to 2.6 eV, respectively. Defects involving Bint are likely to be the source of blue emitters recently observed in regions several microns away from ion-irradiated parts of hBN. Our work sheds light on these recent experiments and introduces a fresh perspective to the field of quantum emitters in hBN-we show that defects related to Bint are potential single-photon emitters that can be intentionally created in hBN.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001465855100001,
title = {Site-Selective Creation of Blue Emitters in Hexagonal Boron Nitride},
author = {Haidong Liang and Yuan Chen and Leyi Loh and Nicholas Lin Quan Cheng and Dmitrii Litvinov and Chengyuan Yang and Yifeng Chen and Zhepeng Zhang and Kenji Watanabe and Takashi Taniguchi and Maciej Koperski and Su Ying Quek and Michel Bosman and Goki Eda and Andrew Anthony Bettiol},
doi = {10.1021/acsnano.5c03423},
times_cited = {0},
issn = {1936-0851},
year = {2025},
date = {2025-04-12},
journal = {ACS NANO},
volume = {19},
number = {15},
pages = {15130-15138},
publisher = {AMER CHEMICAL SOC},
address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA},
abstract = {Hexagonal boron nitride (hBN) has been of great interest due to its ability to host several bright quantum emitters at room temperature. However, the identification of the observed emitters remains challenging due to spectral variability, as well as the lack of atomic defect structure information. In this work, we demonstrate the site-selective creation of blue emitters in exfoliated hBN flakes with high-energy ion irradiation. With the correlation analysis of cryogenic and temperature-dependent photoluminescence (PL) spectroscopy, we observe two zero phonon lines (ZPLs) at similar to 432.8 and 454.3 nm. Photoluminescence excitation (PLE) measurements further confirm the emission origins of the two prominent lines. Scanning transmission electron microscopy (STEM) reveals that the dominant defect structures present in ion-irradiated samples are vacancy-type (V x ) and adatom(intercalant)-type (A x ). Together with first-principles GW-BSE (Bethe-Salpeter equation) calculations, we deduce that the observed blue emissions are likely related to boron intercalants (Bint). Our results not only discover a group of blue emissions in hBN but also provide insights into the physical origin of the emissions with local atomic structures in hBN.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001360396900001,
title = {Nb impurity-bound excitons as quantum emitters in monolayer WS_{2}},
author = {Leyi Loh and Yi Wei Ho and Fengyuan Xuan and Andres Granados del Aguila and Yuan Chen and See Yoong Wong and Jingda Zhang and Zhe Wang and Kenji Watanabe and Takashi Taniguchi and Paul J Pigram and Michel Bosman and Su Ying Quek and Maciej Koperski and Goki Eda},
doi = {10.1038/s41467-024-54360-5},
times_cited = {2},
year = {2024},
date = {2024-11-20},
journal = {NATURE COMMUNICATIONS},
volume = {15},
number = {1},
publisher = {NATURE PORTFOLIO},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {Point defects in crystalline solids behave as optically addressable individual quantum systems when present in sufficiently low concentrations. In two-dimensional (2D) semiconductors, such quantum defects hold potential as versatile single photon sources. Here, we report the synthesis and optical properties of Nb-doped monolayer WS2 in the dilute limit where the average spacing between individual dopants exceeds the optical diffraction limit, allowing the emission spectrum to be studied at the single-dopant level. We show that these individual dopants exhibit common features of quantum emitters, including narrow emission lines (with linewidths <1 meV), strong spatial confinement, and photon antibunching. These emitters consistently occur within a narrow spectral range across multiple samples, distinct from common quantum emitters in van der Waals (vdW) materials that show large ensemble broadening. Analysis of the Zeeman splitting reveals that they can be attributed to bound exciton complexes comprising dark excitons and negatively charged Nb.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001251520000012,
title = {Exciton-Enhanced Spontaneous Parametric Down-Conversion in Two-Dimensional Crystals},
author = {Fengyuan Xuan and Mingrui Lai and Yaze Wu and Su Ying Quek},
doi = {10.1103/PhysRevLett.132.246902},
times_cited = {10},
issn = {0031-9007},
year = {2024},
date = {2024-06-14},
journal = {PHYSICAL REVIEW LETTERS},
volume = {132},
number = {24},
publisher = {AMER PHYSICAL SOC},
address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
abstract = {We show that excitonic resonances and interexciton transitions can enhance the probability of spontaneous parametric down -conversion, a second -order optical response that generates entangled photon pairs. We benchmark our ab initio many -body calculations using experimental polar plots of second harmonic generation in NbOI 2 , clearly demonstrating the relevance of excitons in the nonlinear response. A strong double-exciton resonance in 2D NbOCl 2 leads to giant enhancement in the second order susceptibility. Our work paves the way for the realization of efficient ultrathin quantum light sources.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{ISI:001237790900002,
title = {Evidence for electron-hole crystals in a Mott insulator},
author = {Zhizhan Qiu and Yixuan Han and Keian Noori and Zhaolong Chen and Mikhail Kashchenko and Li Lin and Thomas Olsen and Jing Li and Hanyan Fang and Pin Lyu and Mykola Telychko and Xingyu Gu and Shaffique Adam and Su Ying Quek and Aleksandr Rodin and Castro A H Neto and Kostya S Novoselov and Jiong Lu},
doi = {10.1038/s41563-024-01910-3},
times_cited = {8},
issn = {1476-1122},
year = {2024},
date = {2024-06-03},
journal = {NATURE MATERIALS},
volume = {23},
number = {8},
publisher = {NATURE PORTFOLIO},
address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY},
abstract = {The coexistence of correlated electron and hole crystals enables the realization of quantum excitonic states, capable of hosting counterflow superfluidity and topological orders with long-range quantum entanglement. Here we report evidence for imbalanced electron-hole crystals in a doped Mott insulator, namely, alpha-RuCl3, through gate-tunable non-invasive van der Waals doping from graphene. Real-space imaging via scanning tunnelling microscopy reveals two distinct charge orderings at the lower and upper Hubbard band energies, whose origin is attributed to the correlation-driven honeycomb hole crystal composed of hole-rich Ru sites and rotational-symmetry-breaking paired electron crystal composed of electron-rich Ru-Ru bonds, respectively. Moreover, a gate-induced transition of electron-hole crystals is directly visualized, further corroborating their nature as correlation-driven charge crystals. The realization and atom-resolved visualization of imbalanced electron-hole crystals in a doped Mott insulator opens new doors in the search for correlated bosonic states within strongly correlated materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}