Femtosecond dynamics in layered materials
Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Final Report Abstract
In the framework of this project we developed a cutting-edge experimental setup that employs advanced concepts of nonlinear and ultrafast optics for the generation of ultrashort optical pulses in a spectral window that spans from the UV to the mid-infrared (multi-THz) range. The 50 kHz repetition rate of this system appeared to be an extremely beneficial compromise of high pulse energies and counting statistics, enabling sensitive measurements with samples of reduced dimension. With an advanced modulation and detection scheme, we achieved exceptional sensitivity in the experiments, higher than comparable commercial and scientific systems. Ultrashort optical pulses across the spectrum were exploited for the study of fundamental ultrafast processes occurring in condensed matter in general and layered materials in particular. Some of the physical aspects that we investigated deal with carrier scattering mechanisms at the femtosecond timescale in graphene, carbon nanotubes, semiconductors and high-temperature superconductors, underlining the need for extraordinary specifications achieved by the setup. Based on the PI’s experience in the field of two-dimensional spectroscopy, we implemented the possibility of three-pulse experiments to study many-body effects and energetic correlations of electronic excitations as well as their influence on low energy physics. A particular experiment that exemplifies the research line established with this project shows how few-layer GaSe exhibits optical properties that can be finely tuned by controlling the number of layers in the flakes themselves. In particular, our findings are counterintuitive and set GaSe apart from other layered materials. We observe that in samples containing less than 8 layers the excitonic transitions are strongly suppressed. This is in contrast to the typical exciton enhancement that occurs in semiconductors when the dimensionality approaches an ideal 2D confinement of the electronic wavefunctions. We conclusively explain this peculiar phenomenon with the shaping of the valence band that takes the form of an inverted Mexican hat exactly at the layer number that in the experiments leads to the suppression of excitonic absorption. This understanding of electron-phonon coupling in the dependence of layers is a milestone for the investigation of novel materials and their potential application. We successfully implemented the combination of femtosecond visible spectroscopy with ultrashort THz pulses to study high- and low-energy correlations in a strongly asymmetric spectral configuration. Promising results from novel materials such as the high-temperature superconductor bismuth strontium calcium copper oxide unveil the capabilities of this method and pave the way towards future investigations. These measurements were complemented by a four-wave mixing interferometer in the multi-THz (mid-infrared) spectral region, which gives direct access to the coherent dynamics at low energy and resonant to the superconducting ground state. Field-resolution of the mid-infrared fields provides access to the complex-valued intraband conductivity of the material. The observation of high-order nonlinear processes with unprecedented sensitivity establishes multidimensional spectroscopy for the investigation of novel semiconductors and strongly correlated materials. Our discoveries open, on the one hand, new fundamental perspectives in the field of lightmatter interaction in layered 2D semiconductors. On the other hand, it paves the way for technological strategies for the investigation of functional materials with engineered topology for the development of advanced optoelectronic devices. Many peer-reviewed scientific publications resulted from the experiments performed in the scope of this project. Based on the experiences gained throughout the project, we will continue our investigations in the future.
Publications
- "Below-gap excitation of semiconducting single-wall carbon nanotubes”, Nanoscale 7, 18337 (2015)
G. Soavi, A. Grupp, A. Budweg, F. Scotognella, T. Hefner, T. Hertel, G. Lanzani, A. Leitenstorfer, G. Cerullo, and D. Brida
(See online at https://doi.org/10.1039/c5nr05218a) - "Ultrafast pseudospin dynamics in graphene", Phys. Rev. B 92, 165429 (2015)
M. Trushin, A. Grupp, G. Soavi, A. Budweg, D. De Fazio, U. Sassi, A. Lombardo, A. C. Ferrari, W. Belzig, A. Leitenstorfer, and D. Brida
(See online at https://doi.org/10.1103/PhysRevB.92.165429) - "Coherent Field Transients below 15 THz from Phase-Matched Difference Frequency Generation in 4H-SiC", Opt. Lett. 42, 2687 (2017)
M. P. Fischer, J. Bühler, G. Fitzky, T. Kurihara, S. Eggert, A. Leitenstorfer und D. Brida
(See online at https://doi.org/10.1364/OL.42.002687) - "Incoherent Pathways of Charge Separation in Organic and Hybrid Solar Cells”, J. Phys. Chem. Lett. 8, 4858 (2017)
A. Grupp, P. Ehrenreich, J. Kalb, A. Budweg, L. Schmidt-Mende, and D. Brida
(See online at https://doi.org/10.1021/acs.jpclett.7b01873) - "Broadly tunable ultrafast pump-probe system operating at multi-kHz repetition rate", J. Opt. 20, 014005 (2018)
A. Grupp, A. Budweg, M. P. Fischer, J. Allerbeck, G. Soavi, A. Leitenstorfer, and D. Brida
(See online at https://doi.org/10.1088/2040-8986/aa9b07) - “Plasmonic mid-infrared third harmonic generation in germanium nanoantennas”, Light: Science & Application 7, 106 (2018)
M. P. Fischer, A. Riede, K. Gallacher, J. Frigerio, G. Pellegrini, M. Ortolani, D. J. Paul, G. Isella, A. Leitenstorfer, P. Biagioni, D. Brida
(See online at https://doi.org/10.1038/s41377-018-0108-8) - “Control of excitonic absorption by thickness variation in few-layer GaSe”, Phys. Rev. B 100, 045404 (2019)
A. Budweg, D. Yadav, A. Grupp, A. Leitenstorfer, M. Trushin, F. Pauly, D. Brida
(See online at https://doi.org/10.1103/PhysRevB.100.045404) - “Pump-probe spectroscopy study of ultrafast temperature dynamics in nanoporous gold”, Phys. Rev. B 99, 035435 (2019)
M. Ortolani, A. Mancini, A. Budweg, D. Garoli, D. Brida, F. de Angelis
(See online at https://doi.org/10.1103/PhysRevB.99.035435) - “Ultrafast carrier recombination in highly n-doped Ge-on-Si films“, Appl. Phys. Lett. 114, 241104 (2019)
J. Allerbeck, A. J Herbst, Y. Yamamoto, G. Capellini, M. Virgilio, D. Brida
(See online at https://doi.org/10.1063/1.5088012) - “Ultrafast all-optical switching enabled by epsilon-near-zero-tailored absorption in metal-insulator nanocavities“, Comm. Phys. 3, 114 (2020)
J. Kuttruff, D. Garoli, J. Allerbeck, R. Krahne, A. De Luca, D. Brida, V. Caligiuri, N. Maccaferri
(See online at https://doi.org/10.1038/s42005-020-0379-2)
