Magnetic fields can have profound effects on the motion of electrons in quantum materials. Two-dimensional electron systems subject to strong magnetic fields are expected to exhibit quantized Hall conductivity, chiral edge currents and distinctive collective modes referred to as magnetoplasmons and magnetoexcitons. Generating these propagating collective modes in charge-neutral samples and imaging them at their native nanometre length scales have thus far been experimentally elusive. Here we visualize propagating magnetoexciton polaritons at their native length scales and report their magnetic-field-tunable dispersion in near-charge-neutral graphene. Imaging these collective modes and their associated nano-electro-optical responses allows us to identify polariton-modulated optical and photo-thermal electric effects at the sample edges, which are the most pronounced near charge neutrality. Our work is enabled by innovations in cryogenic near-field optical microscopy techniques that allow for the nano-imaging of the near-field responses of two-dimensional materials under magnetic fields up to 7 T. This nano-magneto-optics approach allows us to explore and manipulate magnetopolaritons in specimens with low carrier doping via harnessing high magnetic fields.
This is a preview of subscription content, access via your institution
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Rent or buy this article
Prices vary by article type
Prices may be subject to local taxes which are calculated during checkout
All codes underlying this study are available from the corresponding authors upon reasonable request.
Peres, N. M. R., Guinea, F. & Castro Neto, A. H. Electronic properties of disordered two-dimensional carbon. Phys. Rev. B Condens. Matter Mater. Phys. 73, 125411 (2006).
Sadowski, M. L., Martinez, G., Potemski, M., Berger, C. & De Heer, W. A. Landau level spectroscopy of ultrathin graphite layers. Phys. Rev. Lett. 97, 266405 (2006).
Jiang, Z. et al. Infrared spectroscopy of Landau levels of graphene. Phys. Rev. Lett. 98, 197403 (2007).
Gusynin, V. P., Sharapov, S. G. & Carbotte, J. P. Magneto-optical conductivity in graphene. J. Phys. Condens. Matter 19, 026222 (2007).
Crassee, I. et al. Giant Faraday rotation in single- and multilayer graphene. Nat. Phys. 7, 48–51 (2011).
Crassee, I. et al. Multicomponent magneto-optical conductivity of multilayer graphene on SiC. Phys. Rev. B Condens. Matter Mater. Phys. 84, 035103 (2011).
Goerbig, M. O. Electronic properties of graphene in a strong magnetic field. Rev. Mod. Phys. 83, 1193 (2011).
Orlita, M. et al. Approaching the Dirac point in high-mobility multilayer epitaxial graphene. Phys. Rev. Lett. 101, 267601 (2008).
Kallin, C. & Halperin, B. I. Excitations from a filled Landau level in the two-dimensional electron gas. Phys. Rev. B 30, 5655 (1984).
Lozovik, Y. E. & Sokolik, A. A. Influence of Landau level mixing on the properties of elementary excitations in graphene in strong magnetic field. Nanoscale Res. Lett. 7, 134 (2012).
Wang, W., Apell, S. P. & Kinaret, J. M. Edge magnetoplasmons and the optical excitations in graphene disks. Phys. Rev. B Condens. Matter Mater. Phys. 86, 125450 (2012).
Andreev, I. V., Muravev, V. M., Semenov, N. D., Zabolotnykh, A. A. & Kukushkin, I. V. Magnetodispersion of two-dimensional plasmon polaritons. Phys. Rev. B 104, 195436 (2021).
Petković, I., Williams, F. I. B. & Glattli, D. C. Edge magnetoplasmons in graphene. J. Phys. D: Appl. Phys. 47, 094010 (2014).
Poumirol, J. M. et al. Electrically controlled terahertz magneto-optical phenomena in continuous and patterned graphene. Nat. Commun. 8, 14626 (2017).
Slipchenko, T. M., Poumirol, J. M., Kuzmenko, A. B., Nikitin, A. Y. & Martín-Moreno, L. Interband plasmon polaritons in magnetized charge-neutral graphene. Commun. Phys. 4, 110 (2021).
Iyengar, A., Wang, J., Fertig, H. A. & Brey, L. Excitations from filled Landau levels in graphene. Phys. Rev. B Condens. Matter Mater. Phys. 75, 125430 (2007).
Keilmann, F. & Hillenbrand, R. Near-field microscopy by elastic light scattering from a tip. Phil. Trans. R. Soc. A 362, 787–805 (2004).
Chen, X. et al. Modern scattering-type scanning near-field optical microscopy for advanced material research. Adv. Mater. 31, 1804774 (2019).
Dapolito, M. et al. Scattering-type scanning near-field optical microscopy with Akiyama piezo-probes. Appl. Phys. Lett. 120, 013104 (2022).
Fei, Z. et al. Edge and surface plasmons in graphene nanoribbons. Nano Lett. 15, 8271–8276 (2015).
Sunku, S. S. et al. Photonic crystals for nano-light in moiré graphene superlattices. Science 362, 1153–1156 (2018).
Lundeberg, M. B. et al. Thermoelectric detection and imaging of propagating graphene plasmons. Nat. Mater. 16, 204–207 (2017).
Jing, R. et al. Terahertz response of monolayer and few-layer WTe2 at the nanoscale. Nat. Commun. 12, 5594 (2021).
Qazilbash, M. M. et al. Mott transition in VO2 revealed by infrared spectroscopy and nano-imaging. Science 318, 1750–1753 (2007).
McLeod, A. S. et al. Nanotextured phase coexistence in the correlated insulator V2O3. Nat. Phys. 13, 80–86 (2017).
Post, K. W. et al. Coexisting first- and second-order electronic phase transitions in a correlated oxide. Nat. Phys. 14, 1056–1061 (2018).
Stinson, H. T. et al. Imaging the nanoscale phase separation in vanadium dioxide thin films at terahertz frequencies. Nat. Commun. 9, 3604 (2018).
Sunku, S. S. et al. Nano-photocurrent mapping of local electronic structure in twisted bilayer graphene. Nano Lett. 20, 2958–2964 (2020).
Woessner, A. et al. Near-field photocurrent nanoscopy on bare and encapsulated graphene. Nat. Commun. 7, 10783 (2016).
Shao, Y. et al. Nonlinear nanoelectrodynamics of a Weyl metal. Proc. Natl Acad. Sci. USA 118, e2116366118 (2021).
Sunku, S. S. et al. Hyperbolic enhancement of photocurrent patterns in minimally twisted bilayer graphene. Nat. Commun. 12, 1641 (2021).
Nedoliuk, I. O., Hu, S., Geim, A. K. & Kuzmenko, A. B. Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material. Nat. Nanotechnol. 14, 756–761 (2019).
Kotov, V. N., Uchoa, B., Pereira, V. M., Guinea, F. & Castri Neto, A. H. Electron-electron interactions in graphene: current status and perspectives. Rev. Mod. Phys. 84, 1067 (2012).
Shizuya, K. Many-body corrections to cyclotron resonance in monolayer and bilayer graphene. Phys. Rev. B 81, 075407 (2010).
Henriksen, E. A. et al. Interaction-induced shift of the cyclotron resonance of graphene using infrared spectroscopy. Phys. Rev. Lett. 104, 067404 (2010).
Xu, X., Gabor, N. M., Alden, J. S., Van Der Zande, A. M. & McEuen, P. L. Photo-thermoelectric effect at a graphene interface junction. Nano Lett. 10, 562–566 (2010).
Checkelsky, J. G. & Ong, N. P. Thermopower and Nernst effect in graphene in a magnetic field. Phys. Rev. B 80, 081413(R) (2009).
Wei, P., Bao, W., Pu, Y., Lau, C. N. & Shi, J. Anomalous thermoelectric transport of Dirac particles in graphene. Phys. Rev. Lett. 102, 166808 (2009).
Lundeberg, M. B. & Koppens, F. H. L. Thermodynamic reciprocity in scanning photocurrent maps. Preprint at https://arxiv.org/abs/2011.04311 (2020).
Cao, H. et al. Photo-Nernst current in graphene. Nat. Phys. 12, 236–239 (2016).
Olbrich, P. et al. Giant photocurrents in a Dirac fermion system at cyclotron resonance. Phys. Rev. B Condens. Matter Mater. Phys. 87, 235439 (2013).
Fei, Z. et al. Gate-tuning of graphene plasmons revealed by infrared nano-imaging. Nature 486, 82–85 (2012).
Alonso-González, P. et al. Acoustic terahertz graphene plasmons revealed by photocurrent nanoscopy. Nat. Nanotechnol. 12, 31–35 (2016).
Giubileo, F. & Di Bartolomeo, A. The role of contact resistance in graphene field-effect devices. Prog. Surf. Sci. 92, 143–175 (2017).
Chen, X. et al. Rapid simulations of hyperspectral near-field images of three-dimensional heterogeneous surfaces—part II. Opt. Express 30, 11228 (2022).
Maissen, C., Chen, S., Nikulina, E., Govyadinov, A. & Hillenbrand, R. Probes for ultrasensitive THz nanoscopy. ACS Photonics 6, 1279–1288 (2019).
Xin, N. et al. Giant magnetoresistance of Dirac plasma in high-mobility graphene. Nature 616, 270–274 (2023).
Li, Q. et al. Chiral magnetic effect in ZrTe5. Nat. Phys. 12, 550–554 (2016).
Tseng, C. C. et al. Gate-tunable proximity effects in graphene on layered magnetic insulators. Nano Lett. 22, 8495–8501 (2022).
Bloch, J., Cavalleri, A., Galitski, V., Hafezi, M. & Rubio, A. Strongly correlated electron–photon systems. Nature 606, 41–48 (2022).
Ma, C. et al. Moiré band topology in twisted bilayer graphene. Nano Lett. 20, 6076–6083 (2020).
Yu, J. et al. Correlated Hofstadter spectrum and flavour phase diagram in magic-angle twisted bilayer graphene. Nat. Phys. 18, 825–831 (2022).
Hu, B., Tao, J., Zhang, Y. & Wang, Q. J. Magneto-plasmonics in graphene-dielectric sandwich. Opt. Express 22, 21727 (2014).
Yan, H. et al. Infrared spectroscopy of tunable Dirac terahertz magneto-plasmons in graphene. Nano Lett. 12, 3766–3771 (2012).
Kim, R. H. J., Park, J.-M., Haeuser, S. J., Luo, L. & Wang, J. A sub-2 Kelvin cryogenic magneto-terahertz scattering-type scanning near-field optical microscope (cm-THz-sSNOM). Rev. Sci. Instrum. 94, 043702 (2023).
Fei, Z. et al. Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface. Nano Lett. 11, 4701–4705 (2011).
Knoll, B. & Keilmann, F. Enhanced dielectric contrast in scattering-type scanning near-field optical microscopy. Opt. Commun. 182, 321–328 (2000).
Purdie, D. G. et al. Cleaning interfaces in layered materials heterostructures. Nat. Commun. 9, 5387 (2018).
Wang, L. et al. One-dimensional electrical contact to a two-dimensional material. Science 342, 614–617 (2013).
M.D., M.K.L. and Q.L. acknowledge support from the DOE, Office of Science, Basic Energy Sciences, Division of Materials Sciences and Engineering (Contract No. DE-SC0012704) for the construction of infrared optics and sample characterization. X.C., M.K.L and D.N.B. acknowledge the support of m-SNOM scanner construction as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the DOE, Office of Science, Basic Energy Sciences (Award DE-SC0019443). M.D., L.W., G.L.C, X.C, D.N.B. and M.K.L. acknowledge support of the Akiyama probe design from the US Department of Energy (DOE), Office of Science, National Quantum Information Science Research Centers, Co-design Center for Quantum Advantage (Contract No. DE-SC0012704). X.D. acknowledges support from the National Science Foundation (Award DMR-1808491). A.B.K. and A.B. are supported by the Swiss National Science Foundation (Grant No. 200020_201096). We are grateful for the helpful discussion and technical support from X. Xu at Lehigh University, D. Martien from Quantum Design, J. Li and W. Wang from Ithatron Optics, X. Wu from the Institute of Physics, Chinese Academy of Sciences, Q. Yang from Jilin University and Q. Sun from Tsinghua University.
M.D., X.C., M.K.L. and A.G. have a patent pending related to the design of the m-SNOM. The other authors declare no competing interests.
Peer review information
Nature Nanotechnology thanks the anonymous reviewers for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
OAP: off-axis parabolic mirror. Tip: Akiyama probe. Light enters the chamber in the horizontal direction (into the field of view) and is focused onto the sample with an OAP.
About this article
Cite this article
Dapolito, M., Tsuneto, M., Zheng, W. et al. Infrared nano-imaging of Dirac magnetoexcitons in graphene. Nat. Nanotechnol. (2023). https://doi.org/10.1038/s41565-023-01488-y