Xueqi Chen

All Publications

• Roadmap for Photonics with 2D Materials. ACS photonics de Abajo, F. J., Basov, D. N., Koppens, F. H., Orsini, L., Ceccanti, M., Castilla, S., Cavicchi, L., Polini, M., Gonçalves, P. A., Costa, A. T., Peres, N. M., Mortensen, N. A., Bharadwaj, S., Jacob, Z., Schuck, P. J., Pasupathy, A. N., Delor, M., Liu, M. K., Mugarza, A., Merino, P., Cuxart, M. G., Chávez-Angel, E., Švec, M., Tizei, L. H., Dirnberger, F., Deng, H., Schneider, C., Menon, V., Deilmann, T., Chernikov, A., Thygesen, K. S., Abate, Y., Terrones, M., Sangwan, V. K., Hersam, M. C., Yu, L., Chen, X., Heinz, T. F., Murthy, P., Kroner, M., Smolenski, T., Thureja, D., Chervy, T., Genco, A., Trovatello, C., Cerullo, G., Dal Conte, S., Timmer, D., De Sio, A., Lienau, C., Shang, N., Hong, H., Liu, K., Sun, Z., Rozema, L. A., Walther, P., Alù, A., Marini, A., Cotrufo, M., Queiroz, R., Zhu, X. Y., Cox, J. D., Dias, E. J., Echarri, Á. R., Iyikanat, F., Herrmann, P., Tornow, N., Klimmer, S., Wilhelm, J., Soavi, G., Sun, Z., Wu, S., Xiong, Y., Matsyshyn, O., Krishna Kumar, R., Song, J. C., Bucher, T., Gorlach, A., Tsesses, S., Kaminer, I., Schwab, J., Mangold, F., Giessen, H., Sánchez, M. S., Efetov, D. K., Low, T., Gómez-Santos, G., Stauber, T., Álvarez-Pérez, G., Duan, J., Martín-Moreno, L., Paarmann, A., Caldwell, J. D., Nikitin, A. Y., Alonso-González, P., Mueller, N. S., Volkov, V., Jariwala, D., Shegai, T., van de Groep, J., Boltasseva, A., Bondarev, I. V., Shalaev, V. M., Simon, J., Fruhling, C., Shen, G., Novko, D., Tan, S., Wang, B., Petek, H., Mkhitaryan, V., Yu, R., Manjavacas, A., Ortega, J. E., Cheng, X., Tian, R., Mao, D., Van Thourhout, D., Gan, X., Dai, Q., Sternbach, A., Zhou, Y., Hafezi, M., Litvinov, D., Grzeszczyk, M., Novoselov, K. S., Koperski, M., Papadopoulos, S., Novotny, L., Viti, L., Vitiello, M. S., Cottam, N. D., Dewes, B. T., Makarovsky, O., Patanè, A., Song, Y., Cai, M., Chen, J., Naveh, D., Jang, H., Park, S., Xia, F., Jenke, P. K., Bajo, J., Braun, B., Burch, K. S., Zhao, L., Xu, X. 2025; 12 (8): 3961-4095

  Abstract

  Triggered by advances in atomic-layer exfoliation and growth techniques, along with the identification of a wide range of extraordinary physical properties in self-standing films consisting of one or a few atomic layers, two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and other van der Waals (vdW) crystals now constitute a broad research field expanding in multiple directions through the combination of layer stacking and twisting, nanofabrication, surface-science methods, and integration into nanostructured environments. Photonics encompasses a multidisciplinary subset of those directions, where 2D materials contribute remarkable nonlinearities, long-lived and ultraconfined polaritons, strong excitons, topological and chiral effects, susceptibility to external stimuli, accessibility, robustness, and a completely new range of photonic materials based on layer stacking, gating, and the formation of moiré patterns. These properties are being leveraged to develop applications in electro-optical modulation, light emission and detection, imaging and metasurfaces, integrated optics, sensing, and quantum physics across a broad spectral range extending from the far-infrared to the ultraviolet, as well as enabling hybridization with spin and momentum textures of electronic band structures and magnetic degrees of freedom. The rapid expansion of photonics with 2D materials as a dynamic research arena is yielding breakthroughs, which this Roadmap summarizes while identifying challenges and opportunities for future goals and how to meet them through a wide collection of topical sections prepared by leading practitioners.

  View details for DOI 10.1021/acsphotonics.5c00353

  View details for PubMedID 40861258

  View details for PubMedCentralID PMC12371959

• Quantum control of exciton wave functions in 2D semiconductors. Science advances Hu, J., Lorchat, E., Chen, X., Watanabe, K., Taniguchi, T., Heinz, T. F., Murthy, P. A., Chervy, T. 2024; 10 (12): eadk6369

  Abstract

  Excitons-bound electron-hole pairs-play a central role in light-matter interaction phenomena and are crucial for wide-ranging applications from light harvesting and generation to quantum information processing. A long-standing challenge in solid-state optics has been to achieve precise and scalable control over excitonic motion. We present a technique using nanostructured gate electrodes to create tailored potential landscapes for excitons in 2D semiconductors, enabling in situ wave function shaping at the nanoscale. Our approach forms electrostatic traps for excitons in various geometries, such as quantum dots, rings, and arrays thereof. We show independent spectral tuning of spatially separated quantum dots, achieving degeneracy despite material disorder. Owing to the strong light-matter coupling of excitons in 2D semiconductors, we observe unambiguous signatures of confined exciton wave functions in optical reflection and photoluminescence measurements. This work unlocks possibilities for engineering exciton dynamics and interactions at the nanometer scale, with implications for optoelectronic devices, topological photonics, and quantum nonlinear optics.

  View details for DOI 10.1126/sciadv.adk6369

  View details for PubMedID 38507493

• Moiré-Assisted Strain Transfer in Vertical van der Waals Heterostructures. Nano letters Hu, J., Yu, L., Chen, X., Lee, W., Mate, C. M., Heinz, T. F. 2023

  Abstract

  Strain provides a powerful method to study 2D monolayers and to tune their properties. The same approach also has great potential for van-der-Waals (vdW) heterostructures. However, we need to understand how strain can be applied to vertically stacked vdW structures, for which strain transfer from one layer to the next remains little explored. In our experiment, we fabricated vertical heterostructures consisting of transition metal dichalcogenides (TMDCs) monolayers that were deposited on a flexible substrate. These TMDC heterostructures allowed us to read out separately the strain in each monolayer by photoluminescence measurements. We find that, in TMDC heterostructures with large twist angles (>5°), strain transfer is limited. However, for aligned heterostructures with small twist angles (≤5°), near unity strain transfer efficiency is observed. We correlate this finding with the moiré domains formed in the aligned heterostructures by reconstruction.

  View details for DOI 10.1021/acs.nanolett.3c03388

  View details for PubMedID 37903015

• Optical absorption of interlayer excitons in transition-metal dichalcogenide heterostructures. Science (New York, N.Y.) Barre, E., Karni, O., Liu, E., O'Beirne, A. L., Chen, X., Ribeiro, H. B., Yu, L., Kim, B., Watanabe, K., Taniguchi, T., Barmak, K., Lui, C. H., Refaely-Abramson, S., da Jornada, F. H., Heinz, T. F. 2022; 376 (6591): 406-410

  Abstract

  Interlayer excitons, electron-hole pairs bound across two monolayer van der Waals semiconductors, offer promising electrical tunability and localizability. Because such excitons display weak electron-hole overlap, most studies have examined only the lowest-energy excitons through photoluminescence. We directly measured the dielectric response of interlayer excitons, which we accessed using their static electric dipole moment. We thereby determined an intrinsic radiative lifetime of 0.40 nanoseconds for the lowest direct-gap interlayer exciton in a tungsten diselenide/molybdenum diselenide heterostructure. We found that differences in electric field and twist angle induced trends in exciton transition strengths and energies, which could be related to wave function overlap, moire confinement, and atomic reconstruction. Through comparison with photoluminescence spectra, this study identifies a momentum-indirect emission mechanism. Characterization of the absorption is key for applications relying on light-matter interactions.

  View details for DOI 10.1126/science.abm8511

  View details for PubMedID 35446643