Stanford Advisors

Current Research and Scholarly Interests

My current research focuses on light-matter interactions on extremely fast time scales (femto- and attoseconds). This includes ultrafast current injection and the generation of high harmonics in two-dimensional materials like TMDCs and layered heterostructures.

All Publications

  • Strong-Field Bloch Electron Interferometry for Band-Structure Retrieval. Physical review letters Weitz, T., Heide, C., Hommelhoff, P. 2024; 132 (20): 206901


    When Bloch electrons in a solid are exposed to a strong optical field, they are coherently driven in their respective bands where they acquire a quantum phase as the imprint of the band shape. If an electron approaches an avoided crossing formed by two bands, it may be split by undergoing a Landau-Zener transition. We here employ subsequent Landau-Zener transitions to realize strong-field Bloch electron interferometry, allowing us to reveal band structure information. In particular, we measure the Fermi velocity (band slope) of graphene in the vicinity of the K points as (1.07±0.04)nmfs^{-1}. We expect strong-field Bloch electron interferometry for band structure retrieval to apply to a wide range of material systems and experimental conditions, making it suitable for studying transient changes in band structure with femtosecond temporal resolution at ambient conditions.

    View details for DOI 10.1103/PhysRevLett.132.206901

    View details for PubMedID 38829079

  • Giant room-temperature nonlinearities in a monolayer Janus topological semiconductor. Nature communications Shi, J., Xu, H., Heide, C., HuangFu, C., Xia, C., de Quesada, F., Shen, H., Zhang, T., Yu, L., Johnson, A., Liu, F., Shi, E., Jiao, L., Heinz, T., Ghimire, S., Li, J., Kong, J., Guo, Y., Lindenberg, A. M. 2023; 14 (1): 4953


    Nonlinear optical materials possess wide applications, ranging from terahertz and mid-infrared detection to energy harvesting. Recently, the correlations between nonlinear optical responses and certain topological properties, such as the Berry curvature and the quantum metric tensor, have attracted considerable interest. Here, we report giant room-temperature nonlinearities in non-centrosymmetric two-dimensional topological materials-the Janus transition metal dichalcogenides in the 1 T' phase, synthesized by an advanced atomic-layer substitution method. High harmonic generation, terahertz emission spectroscopy, and second harmonic generation measurements consistently show orders-of-the-magnitude enhancement in terahertz-frequency nonlinearities in 1 T' MoSSe (e.g., > 50 times higher than 2H MoS2 for 18th order harmonic generation; > 20 times higher than 2H MoS2 for terahertz emission). We link this giant nonlinear optical response to topological band mixing and strong inversion symmetry breaking due to the Janus structure. Our work defines general protocols for designing materials with large nonlinearities and heralds the applications of topological materials in optoelectronics down to the monolayer limit.

    View details for DOI 10.1038/s41467-023-40373-z

    View details for PubMedID 37587120

    View details for PubMedCentralID 8282873

  • High-harmonic generation from artificially stacked 2D crystals NANOPHOTONICS Heide, C., Kobayashi, Y., Johnson, A. C., Heinz, T. F., Reis, D. A., Liu, F., Ghimire, S. 2023
  • Floquet engineering of strongly driven excitons in monolayer tungsten disulfide NATURE PHYSICS Kobayashi, Y., Heide, C., Johnson, A. C., Tiwari, V., Liu, F., Reis, D. A., Heinz, T. F., Ghimire, S. 2023
  • Intense infrared lasers for strong-field science ADVANCES IN OPTICS AND PHOTONICS Chang, Z., Fang, L., Fedorov, V., Geiger, C., Ghimire, S., Heide, C., Ishii, N., Itatani, J., Joshi, C., Kobayashi, Y., Kumar, P., Marra, A., Mirov, S., Petrushina, I., Polyanskiy, M., Reis, D. A., Tochitsky, S., Vasilyev, S., Wang, L., Wu, Y., Zhou, F. 2022; 14 (4): 652-782

    View details for DOI 10.1364/AOP.454797

    View details for Web of Science ID 000917420400001

  • In-Situ Nanoscale Focusing of Extreme Ultraviolet Solid-State High Harmonics PHYSICAL REVIEW X Korobenko, A., Rashid, S., Heide, C., Naumov, A., Reis, D. A., Berini, P., Corkum, P. B., Vampa, G. 2022; 12 (4)
  • Probing topological phase transitions using high-harmonic generation NATURE PHOTONICS Heide, C., Kobayashi, Y., Baykusheva, D. R., Jain, D., Sobota, J. A., Hashimoto, M., Kirchmann, P. S., Oh, S., Heinz, T. F., Reis, D. A., Ghimire, S. 2022
  • Probing electron-hole coherence in strongly driven 2D materials using high-harmonic generation OPTICA Heide, C., Kobayashi, Y., Johnson, A. C., Liu, F., Heinz, T. F., Reis, D. A., Ghimire, S. 2022; 9 (5): 512-516
  • Light-field control of real and virtual charge carriers. Nature Boolakee, T., Heide, C., Garzon-Ramirez, A., Weber, H. B., Franco, I., Hommelhoff, P. 2022; 605 (7909): 251-255


    Light-driven electronic excitation is a cornerstone for energy and information transfer. In the interaction of intense and ultrafast light fields with solids, electrons may be excited irreversibly, or transiently during illumination only. As the transient electron population cannot be observed after the light pulse is gone, it is referred to as virtual, whereas the population that remains excited is called real1-4. Virtual charge carriers have recently been associated with high-harmonic generation and transient absorption5-8, but photocurrent generation may stem from real as well as virtual charge carriers9-14. However, a link between the generation of thecarrier types and their importance for observables of technological relevance is missing. Here we show that real and virtual charge carriers can be excited and disentangled in the optical generation of currents in a gold-graphene-gold heterostructure using few-cycle laser pulses. Depending on the waveform used for photoexcitation, real carriers receive net momentum and propagate to the gold electrodes, whereas virtual carriers generate a polarization response read out at the gold-graphene interfaces. On the basis of these insights, we further demonstrate a proof of concept of a logic gate for future lightwave electronics. Our results offer a direct means to monitor and excite real and virtual charge carriers. Individual control over each type of carrier will markedly increase the integrated-circuit design space and bring petahertz signal processing closer to reality15,16.

    View details for DOI 10.1038/s41586-022-04565-9

    View details for PubMedID 35546189

  • Electronic Coherence and Coherent Dephasing in the Optical Control of Electrons in Graphene. Nano letters Heide, C., Eckstein, T., Boolakee, T., Gerner, C., Weber, H. B., Franco, I., Hommelhoff, P. 2021


    Electronic coherence is of utmost importance for the access and control of quantum-mechanical solid-state properties. Using a purely electronic observable, the photocurrent, we measure a lower bound of the electronic coherence time of 22 ± 4 fs in graphene. The photocurrent is ideally suited to measure electronic coherence, as it is a direct result of coherent quantum-path interference, controlled by the delay between two ultrashort two-color laser pulses. The maximum delay for which interference between the population amplitude injected by the first pulse interferes with that generated by the second pulse determines the electronic coherence time. In particular, numerical simulations reveal that the experimental data yields a lower bound on the electronic coherence time, masked by coherent dephasing due to the broadband absorption in graphene. We expect that our results will significantly advance the understanding of coherent quantum control in solid-state systems ranging from excitation with weak fields to strongly driven systems.

    View details for DOI 10.1021/acs.nanolett.1c02538

    View details for PubMedID 34735774

  • Optical current generation in graphene: CEP control vs. omega + 2 omega control NANOPHOTONICS Heide, C., Boolakee, T., Eckstein, T., Hommelhoff, P. 2021; 10 (14): 3701-3707
  • Light field-driven electron dynamics in 2D-materials Boolakee, T., Heide, C., Weber, H. B., Hommelhoff, P., IEEE IEEE. 2021
  • The effect of photo-carrier doping on the generation of high harmonics from MoS2 Heide, C., Kobayashi, Y., Liu, F., Ghimire, S., Heinz, T. F., Reis, D. A., IEEE IEEE. 2021