Periodic Reporting for period 4 - UpTEMPO (Ultrafast tunneling microscopy by optical field control of quantum currents)
Période du rapport: 2024-03-01 au 2025-02-28
In this project, we implemented a scanning tunnelling microscope (STM) fully driven by the electric field of single cycle light pulses. In this way, we aim at measuring ultrafast phenomena occurring on a timescale of few femtoseconds with a spatial resolution down to individual atoms.
This goal was achieved by generating light pulses that consist in a single cycle of the electromagnetic oscillation. These transients can be focused on an STM tip to act as the source of the bias that drives the current through the sample under investigation with atomic resolution. The ultrafast STM can then be used in combination with other ultrashort pulses employed to excite the samples to probe and derive movies of the charge motions in molecules and nanostructures. The final goal that will be pursued beyond the dureation of funding is to better understand and harness fundamental processes like charge localization and germination with applications that range from sensing to photovoltaics.
This goal was achieved by generating light pulses that consist in a single cycle of the electromagnetic oscillation. These transients can be focused on an STM tip to act as the source of the bias that drives the current through the sample under investigation with atomic resolution. The ultrafast STM can then be used in combination with other ultrashort pulses employed to excite the samples to probe and derive movies of the charge motions in molecules and nanostructures. The final goal that will be pursued beyond the dureation of funding is to better understand and harness fundamental processes like charge localization and germination with applications that range from sensing to photovoltaics.
The novel technique developed in this project, requires the setup of a suitable laser source and of a scanning tunnelling microscope (STM) capable of being coupled with the ultrashort light pulses. These tasks were successfully completed (main publications: Nature Physics 16 (3), 341-345 and Nanophotonics 13 (15), 2803-2809 with several other technological papers and conference proceedings). We are being able to generate ultrabroadband spectra supporting durations down to a single cycle and the STM has been tested in combination with an optical pulse train. The two subsystems have been combined and we are able to generate sub-optical-cycle currents in the in the STM. The STM has also been equipped to operate at cryogenic temperature (a paper is under preparation). This approach will improve the demodulation of the signal is as the last step before proceeding to the final goal of measuring ultrafast dynamics with atomic resolution.
The task of performing pump-probe experiments has not been possible given the extreme difficulties in the optimization of the system. However, there are no fundamental limitations and the efforts will continue.
The task of performing pump-probe experiments has not been possible given the extreme difficulties in the optimization of the system. However, there are no fundamental limitations and the efforts will continue.
We developed an innovative laser platform for the generation of single cycle pulses and achieved the all-optical drive of a scanning tunnelling microscope at near-IR frequencies and at low temperature.