Periodic Reporting for period 1 - QUMATTO (Quantum Materials Probed with Attosecond Optoelectronics)
Berichtszeitraum: 2021-10-15 bis 2023-10-14
The feasibility to sculpt light at the level of individual oscillations has allowed sub-femtosecond (1fs = 10-15s) monitoring and control of electron dynamics in gas phase [Rev. Mod. Phys. 81 (2009)]. Recently, such technology and the theory that underpins it is being transferred into the solid state.
The project QUMATTO combines theory and experiment to bring strong-field physics into lightwave control of quantum properties in crystals. One of the key aims of this project is the use of strong, polarization-tailored fields with spatial symmetry matching the symmetry of the crystal lattice in order to modify the electronic and topological properties of the crystal on ultrafast timescales. During the Action, we demonstrated few-femtosecond control over the bandstructure properties of hexagonal materials using trefoil-symmetric laser fields. In particular, we realized non-resonant control of the valley pseudospin in a hexagonal boron nitride monolayer [arXiv:2303.13044] as well as in bulk MoS2 [arXiv:2302.12564].
Probing of the electronic dynamics in the laser-modified material is achieved via high harmonic generation (HHG), where the sub-laser-cycle electron motion is mapped onto the properties of the light emitted by the oscillating dipole of the driven system [Nat. Phys. 15 (2019)]. Current theoretical modelling of HHG in solids is framed in the reciprocal space, and based on the generation of non-linear currents through intraband electron motion and interband electron-hole recombination processes [Phys. Rev. Lett. 113 (2014); Nature 523 (2015)]. Yet, this framework fails for materials with complex band structures, e.g. very dense or with multiple band crossings. During the Action, we performed HHG experiments in bulk ReS2, a complex material with a dense and flat band structure. The HHG yield showed a strong intensity-dependent anisotropy, in contrast to other prototypical materials like MgO or ZnO. To explain this, we developed an orbital-based framework of HHG in crystals that allowed us to interpret such sharp anisotropic features as interference of currents generated by the different atoms in the unit cell, as well as to show that the contribution of particular atoms to the HHG emission can be enhanced or suppressed by tuning the laser parameters [arXiv:2309.06290] providing an unprecedented atomic perspective of strong-field dynamics in crystals.
The duration of the Action was of 17.5 months due to an early termination of the Agreement.
The project QUMATTO combines theory and experiment to bring strong-field physics into lightwave control of quantum properties in crystals. One of the key aims of this project is the use of strong, polarization-tailored fields with spatial symmetry matching the symmetry of the crystal lattice in order to modify the electronic and topological properties of the crystal on ultrafast timescales. During the Action, we demonstrated few-femtosecond control over the bandstructure properties of hexagonal materials using trefoil-symmetric laser fields. In particular, we realized non-resonant control of the valley pseudospin in a hexagonal boron nitride monolayer [arXiv:2303.13044] as well as in bulk MoS2 [arXiv:2302.12564].
Probing of the electronic dynamics in the laser-modified material is achieved via high harmonic generation (HHG), where the sub-laser-cycle electron motion is mapped onto the properties of the light emitted by the oscillating dipole of the driven system [Nat. Phys. 15 (2019)]. Current theoretical modelling of HHG in solids is framed in the reciprocal space, and based on the generation of non-linear currents through intraband electron motion and interband electron-hole recombination processes [Phys. Rev. Lett. 113 (2014); Nature 523 (2015)]. Yet, this framework fails for materials with complex band structures, e.g. very dense or with multiple band crossings. During the Action, we performed HHG experiments in bulk ReS2, a complex material with a dense and flat band structure. The HHG yield showed a strong intensity-dependent anisotropy, in contrast to other prototypical materials like MgO or ZnO. To explain this, we developed an orbital-based framework of HHG in crystals that allowed us to interpret such sharp anisotropic features as interference of currents generated by the different atoms in the unit cell, as well as to show that the contribution of particular atoms to the HHG emission can be enhanced or suppressed by tuning the laser parameters [arXiv:2309.06290] providing an unprecedented atomic perspective of strong-field dynamics in crystals.
The duration of the Action was of 17.5 months due to an early termination of the Agreement.
During the reporting period we achieved the set scientific goals. A major breakthrough was the experimental demonstration of few-femtosecond controllable band structure engineering using polarization-tailored strong fields in hexagonal boron nitride (hBN) and MoS2. We used a light field composed of a circularly-polarized pulse and its counter-rotating second harmonic, generating a trefoil shape in space that matched the symmetry of the crystal lattice. By changing the time delay between the two pulses, the trefoil rotates in space, allowing to control fundamental symmetries of the dressed system, i.e. inversion and time-reversal (see Figure). In this way, we were able to: (i) realize the light-dressed analogue of the Haldane topological model in hBN, where the valley band gaps can be controlled on sub-laser-cycle timescales, (ii) demonstrate valley polarization in bulk MoS2, extending valleytronics to inversion-symmetric materials. These milestones were achieved in collaboration with the groups of, respectively, (i) Matthias Kling at Max Planck Institute for Quantum Optics (Munich, Germany) and (ii) Jens Biegert at the Institute of Photonic Sciences (ICFO, Barcelona, Spain).
Another milestone was achieved by combining angle-resolved HHG experiments performed on ReS2 flakes and a newly developed real-space framework of high harmonic generation in solids. This allowed us to resolve the attosecond dynamics responsible for high-harmonic emission on each atom of the unit cell of a ReS2 crystal, thus with picometer resolution. We demonstrated that interferences between the atomic currents in the lattice crucially determine the macroscopic emission, and can be manipulated with the parameters of the driving field (intensity and polarization), allowing to select high-harmonic emission from particular atomic orbitals.
Other highlights of this project included: (i) a theoretical proposal for a coherent control scheme that uses time and polarization-controlled short pulses to create an all-optical valley switch operating on less than 100fs, (ii) an extension of the reconstruction of attosecond beating by interference of two photon transitions (RABBIT) technique to solids, (iii, work in progress) HHG experiments on TiSe2 flakes to probe the (2x2x2) charge density wave transition occurring at cold temperatures (~200K). Also, we provided theoretical support to HHG measurements in atomic gases and solids using the codes developed in [R.E.F. Silva et al., Phys. Rev. B 100 (2019); S. Patchkovskii et al., Comput. Phys. Commun. 199 (2016)].
In the reporting period, we produced 5 peer-reviewed articles and another 5 that are currently under review. The results were disseminated in four scientific conferences, four seminars and two news reports.
Another milestone was achieved by combining angle-resolved HHG experiments performed on ReS2 flakes and a newly developed real-space framework of high harmonic generation in solids. This allowed us to resolve the attosecond dynamics responsible for high-harmonic emission on each atom of the unit cell of a ReS2 crystal, thus with picometer resolution. We demonstrated that interferences between the atomic currents in the lattice crucially determine the macroscopic emission, and can be manipulated with the parameters of the driving field (intensity and polarization), allowing to select high-harmonic emission from particular atomic orbitals.
Other highlights of this project included: (i) a theoretical proposal for a coherent control scheme that uses time and polarization-controlled short pulses to create an all-optical valley switch operating on less than 100fs, (ii) an extension of the reconstruction of attosecond beating by interference of two photon transitions (RABBIT) technique to solids, (iii, work in progress) HHG experiments on TiSe2 flakes to probe the (2x2x2) charge density wave transition occurring at cold temperatures (~200K). Also, we provided theoretical support to HHG measurements in atomic gases and solids using the codes developed in [R.E.F. Silva et al., Phys. Rev. B 100 (2019); S. Patchkovskii et al., Comput. Phys. Commun. 199 (2016)].
In the reporting period, we produced 5 peer-reviewed articles and another 5 that are currently under review. The results were disseminated in four scientific conferences, four seminars and two news reports.
The stacking and twisting of atom-thin structures with matching crystal symmetry has provided a unique handle to create new superlattice structures in which new quantum properties emerge. It is now widely accepted that atom-thin quantum materials will be key for quantum electronics. At the same time, the ability to manipulate coherent electron motion with strong light fields holds great potential in quantum electronics. Controlling electronic properties of quantum materials on ultrafast timescales paves the way to petahertz-speed devices operating at room temperature.
In this project, we established a tailored lightwave-driven analogue to twisted layer stacking. Twisting the lightwave relative to the lattice orientation enables switching between band configurations, providing unprecedented control over the magnitude and location of the band gap, and curvature. Our work marks a new direction towards ultrafast quantum devices, combining recent advances in laser and material engineering to manipulate the parameters of the laser-dressed material Hamiltonian on sub-laser-cycle timescales. We demonstrated that this grants universal (non-resonant), symmetry-driven, sub-femtosecond control of the electronic properties of 2D materials. Besides providing a novel building block for future quantum devices, our work also opens far reaching possibilities in fundamental studies, to name a few, real-time creation and monitoring of laser-driven (dynamical) topological phase transitions, control of laser-driven (anomalous) edge states or creation of laser-induced flat-bands.
At the same time, the newly developed real-space dynamical framework of high-harmonic emission from solids opens the way to sub-laser-cycle resolution and control of electron dynamics in solids at the picometer-scale. Far-reaching implications of this work include characterizing topological characteristics in the highly-non equilibrium regime, thanks to the possibility to resolve in real-time the orbital contribution in the high-harmonic spectrum, complementing X-ray/optical wave mixing experiments, or engineering more efficient, solid-state, harmonic sources.
In this project, we established a tailored lightwave-driven analogue to twisted layer stacking. Twisting the lightwave relative to the lattice orientation enables switching between band configurations, providing unprecedented control over the magnitude and location of the band gap, and curvature. Our work marks a new direction towards ultrafast quantum devices, combining recent advances in laser and material engineering to manipulate the parameters of the laser-dressed material Hamiltonian on sub-laser-cycle timescales. We demonstrated that this grants universal (non-resonant), symmetry-driven, sub-femtosecond control of the electronic properties of 2D materials. Besides providing a novel building block for future quantum devices, our work also opens far reaching possibilities in fundamental studies, to name a few, real-time creation and monitoring of laser-driven (dynamical) topological phase transitions, control of laser-driven (anomalous) edge states or creation of laser-induced flat-bands.
At the same time, the newly developed real-space dynamical framework of high-harmonic emission from solids opens the way to sub-laser-cycle resolution and control of electron dynamics in solids at the picometer-scale. Far-reaching implications of this work include characterizing topological characteristics in the highly-non equilibrium regime, thanks to the possibility to resolve in real-time the orbital contribution in the high-harmonic spectrum, complementing X-ray/optical wave mixing experiments, or engineering more efficient, solid-state, harmonic sources.