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Status and perspectives of the FERMI FEL facility (2019)
Luca Giannessi, E. Allaria, Laura Badano, S. Bassanese, Filippo Bencivenga, Carlo Callegari, Flavio Capotondi, Davide Castronovo, F. Cilento, Paolo Cinquegrana, Giovanni De Ninno, Primož Rebernik Ribič, 2019, objavljeni znanstveni prispevek na konferenci

Najdeno v: osebi
Ključne besede: free-electron lasers, harmonic generation
Objavljeno: 15.01.2020; Ogledov: 1215; Prenosov: 46
URL Polno besedilo (0,00 KB)
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Coupling of autoionizing states by a chirped laser pulse
Barbara Ressel, Jurij Urbančič, Primož Rebernik Ribič, Špela Krušič, Žiga Barba, Mateja Hrast, Klemen Bučar, Andrej Mihelič, Matjaž Žitnik, Matija Stupar, David Gauthier, Giovanni De Ninno, 2020, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: We have observed the autoionization of the laser-coupled 2s2p 1Po and 2p2 1Se resonances in helium. The ions were collected while varying the frequency and delay of the extreme-ultraviolet (EUV) excitation pulse with respect to the linearly chirped visible (VIS) laser pulse. From the measured frequency-delay map the Autler- Townes splitting, the EUV-VIS cross-correlation and the linear chirp parameter were extracted.
Najdeno v: osebi
Ključne besede: High Harmonic Generation
Objavljeno: 29.06.2020; Ogledov: 1175; Prenosov: 0
.pdf Polno besedilo (654,72 KB)

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Dissecting Mott and charge-density wave dynamics in the photoinduced phase of 1T-TaS[sub]2
Alberto Simoncig, Matija Stupar, Barbara Ressel, Tanusree Saha, Primož Rebernik Ribič, Giovanni De Ninno, 2021, izvirni znanstveni članek

Opis: The two-dimensional transition-metal dichalcogenide 1T−TaS2 is a complex material standing out for its puzzling low temperature phase marked by signatures amenable to both Mott-insulating and charge-density wave states. Electronic Mott states, coupled to a lattice, respond to coherent optical excitations via a modulation of the lower (valence) Hubbard band. Such dynamics is driven by strong electron-phonon coupling and typically lasts for tens of picoseconds, mimicking coherent structural distortions. Instead, the response occurring at the much faster timescale, mainly dominated by electronic many-body effects, is still a matter of intense research. By performing time- and angle-resolved photoemission spectroscopy, we investigated the photoinduced phase of 1T−TaS2 and found out that its lower Hubbard band promptly reacts to coherent optical excitations by shifting its binding energy towards a slightly larger value. This process lasts for a time comparable to the optical pump pulse length, mirroring a transient change of the onsite Coulomb repulsion energy (U). Such an observation suggests that the correction to the bare value of U, ascribed to the phonon-mediated screening which slightly opposes the Hubbard repulsion, is lost within an interval of a few tens of femtoseconds and can be understood as a fingerprint of electronic states largely decoupled from the lattice. Additionally, these results enforce the hypothesis, envisaged in the current literature, that the transient photoinduced states belong to a sort of crossover phase instead of an equilibrium metallic one.
Najdeno v: osebi
Ključne besede: ultrafast phenomena, time resolved photoemission, strongly correlated systems, transition metal dichalcogenide
Objavljeno: 13.04.2021; Ogledov: 455; Prenosov: 0
.pdf Polno besedilo (1,34 MB)

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Orbital selective dynamics in Fe-pnictides triggered by polarized pump pulse excitations
Kalobaran Maiti, A. Thamizhavel, Giovanni De Ninno, Jurij Urbančič, Barbara Ressel, Matija Stupar, Primož Rebernik Ribič, Tanusree Saha, Ganesh Adhikary, 2021, izvirni znanstveni članek

Opis: Quantum materials display exotic behaviours related to the interplay between temperature-driven phase transitions. Here, we study the electron dynamics in one such material, CaFe$_2$As$_2$, a parent Fe-based superconductor, employing time and angle-resolved photoemission spectroscopy. CaFe$_2$As$_2$ exhibits concomitant transition to spin density wave state and tetragonal to orthorhombic structure below 170 K. The Fermi surface of this material consists of three hole pockets ($\alpha$, $\beta$ and $\gamma$) around $\Gamma$-point and two electron pockets around $X$-point. The hole pockets have $d_{xy}$, $d_{yz}$ and $d_{zx}$ orbital symmetries. The $\beta$ band constituted by $d_{xz}$/$d_{yz}$ orbitals exhibit a gap across the magnetic phase transition. We discover that polarized pump pulses can induce excitations of electrons of a selected symmetry. More specifically, while $s$-polarized light (polarization vector perpendicular to the $xz$-plane) excites electrons corresponding to all the three hole bands, $p$-polarized light excites electrons essentially from ($\alpha$,$\beta$) bands which are responsible for magnetic order. Interestingly, within the magnetically ordered phase, the excitation due to the $p$-polarized pump pulses occur at a time scale of 50 fs, which is significantly faster than the excitation induced by $s$-polarized light ($\sim$ 200 fs). These results suggest that the relaxation of different ordered phases occurs at different time scales and this method can be used to achieve selective excitations to disentangle complexity in the study of quantum materials.
Najdeno v: osebi
Ključne besede: Electronic structure, Pnictides and chalcogenides, Time-resolved spectroscopy
Objavljeno: 13.10.2021; Ogledov: 136; Prenosov: 0
.pdf Polno besedilo (9,56 MB)

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