Prof. Giancarlo Soavi Profile

Prof. Giancarlo Soavi

at Friedrich-Schiller Univ Jena

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Publications (3)

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Proceedings Article | 11 June 2024 Presentation

Tunable photonic nanostructures based on atomically thin semiconductors

Alexey Ustinov, Anna Fedotova, Katsuya Tanaka, Vipin Krishna, Duk-Yong Choi, Giancarlo Soavi, Frank Setzpfandt, Thomas Pertsch, Isabelle Staude

Proceedings Volume PC12990, PC129901F (2024) https://doi.org/10.1117/12.3017523

KEYWORDS: Photonic nanostructures, Nanophotonics, Semiconductors, Dielectrics, Transmittance, Transition metals, Solid state electronics, Photoluminescence, Optical circuits, Nanotechnology

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Hybrid nanophotonic systems consisting of resonant dielectric nanostructures integrated with single or few layers of transition metal dichalcogenides (2D-TMDs) offer important opportunities for active nanophotonic systems featuring an actively tunable response. While the resonant nanophotonic structures serve to enhance the light-matter interaction in the atomically thin membranes, the 2D-TMDs exhibit tunable excitonic properties. However, the experimental realization and demonstration of active functionalities in such hybrid systems remains challenging. Here, we experimentally realize resonant high-index dielectric meta-waveguides and metasurfaces integrated with various species of 2D-TMDs. We demonstrate voltage tuning of the systems’ transmittance and photoluminescent properties, as well as of their polarization dependence. Our results show that hybridization with 2D-TMDs can serve to render resonant photonic nanostructures tunable and time-variant – important properties for practical applications in optical analog computers and neuromorphic circuits.

Proceedings Article | 11 June 2024 Presentation

Nonlinear valleytronics in atomically thin semiconductors

Giancarlo Soavi

Proceedings Volume PC12991, PC1299107 (2024) https://doi.org/10.1117/12.3018153

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In monolayer Transition Metal Dichalcogenides (TMDs), the interplay between space-inversion and Time-Reversal (TR) symmetry defines the spin-valley degree of freedom: direct transitions at the ±K valleys are energetically degenerate but non-equivalent. Thus, engineering of TR symmetry naturally leads to the field of valleytronics, a new type of information technology that allows to manipulate data at the speed of ultrashort light pulses. However, all the methods that have been developed to date for the detection of a Valley Polarization (VP) are based on linear optics and suffer from severe limitations. In this talk, I will discuss a new method for the detection of broken TR symmetry and VP in TMDs based on nonlinear optics. I will show that the VP can be measured from a rotation in the polarization angle of the Second Harmonic (SH) signal emitted from the ±K valleys of a TMD monolayer. In addition, I will show signatures of valley polarization-electric dipole interference and demonstrate that this is a direct consequence of a phase-mismatch between the intrinsic (broken space-inversion symmetry) and valley (broken TR symmetry) terms of the second order nonlinear susceptibility.

Proceedings Article | 30 March 2020 Presentation

Ultrafast nonlinear optical properties of gated graphene (Conference Presentation)

Giancarlo Soavi

Proceedings Volume 11346, 113460M (2020) https://doi.org/10.1117/12.2559860

KEYWORDS: Ultrafast phenomena, Graphene, Nonlinear optics, Harmonic generation, Metalloids, Switches, Frequency converters, Scattering, Phonons

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The recent demonstration of gate tuneable third harmonic generation (THG) in single layer graphene (SLG) has sparked renewed interest in the study of the nonlinear optical properties of 2D materials and Dirac semimetals. Interestingly, our results also suggest new routes towards the realization of on-chip integrated nonlinear devices based on SLG, such as broadband gate tuneable nonlinear optical switches. However, a major limiting factor in this regard, which heavily suppresses the efficiency of such devices, is the increase of the SLG electronic temperature that follows from interaction with ultrashort (fs-ps) pulses. The study of the ultrafast hot electron dynamics in SLG is thus crucial both for the understanding of its nonlinear optical properties and for the realization of nonlinear optical devices such as frequency converters and saturable absorbers. In this talk I will discuss our current understanding of the interplay between hot electrons and nonlinear optics in SLG, focusing in particular on the process of THG. In SLG, the THG intensity can be tuned by over one order of magnitude by externally applied gate voltages. This enhancement is due to logarithmic resonances in the imaginary part of the nonlinear optical conductivity arising from multiphoton resonant transitions. However, both the THG intensity and its power dependence are heavily affected by an increase in the electronic temperature. I will demonstrate that hot electrons are responsible of a two-orders of magnitude reduction of the THG intensity and of a stark deviation from the cubic power law expected for THG. Finally, I will discuss possible configurations to control the hot electron recombination dynamics. These include interlayer electron-phonon interactions and gate tuning of the SLG chemical potential due to phase-space suppression of the hot electron scattering with optical phonons.

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