Larissa Boie

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Boie

First Name

Larissa

ORCID

0000-0002-1991-3980

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Publications 1 - 10 of 11

Coherent manipulation of the effective mass via phonon excitation in the compensated semimetal WTe2
Savoini, Matteo; Beaud, P.; Cilento, Federico; et al. (2023)
Photoinduced structural dynamics of multiferroic TbMnO3
Abreu, Elsa; Savoini, Matteo; Boie, Larissa; et al. (2022)
Physical Review B
We use time-resolved hard x-ray diffraction to investigate the structural dynamics of the multiferroic insulator TbMnO3 in the low-temperature antiferromagnetic and ferroelectrically ordered phase. The lattice response following photoexcitation at 1.55 eV is detected by measuring the (0 2 4) and (1 3 -5) Bragg reflections. A 0.022% tensile strain, normal to the surface, is seen to arise within 20-40 ps. The magnitude of this transient strain is over an order of magnitude lower than that predicted from laser-induced heating, which we attribute to a bottleneck in the energy transfer between the electronic and lattice subsystems. The timescale for the transient expansion is consistent with that of previously reported demagnetization dynamics. We discuss a possible relationship between structural and demagnetization dynamics in TbMnO3, in which photoinduced atomic motion modulates the exchange interaction, leading to a destruction of the magnetic order in the system.
Terahertz displacive excitation of a coherent Raman-active phonon in V2O3
Giorgianni, Flavio; Udina, Mattia; Cea, Tommaso; et al. (2022)
Communications Physics
Nonlinear processes involving frequency-mixing of light fields set the basis for ultrafast coherent spectroscopy of collective modes in solids. In certain semimetals and semiconductors, generation of coherent phonon modes can occur by a displacive force on the lattice at the difference-frequency mixing of a laser pulse excitation on the electronic system. Here, as a low-frequency counterpart of this process, we demonstrate that coherent phonon excitations can be induced by the sum-frequency components of an intense terahertz light field, coupled to intraband electronic transitions. This nonlinear process leads to charge-coupled coherent dynamics of Raman-active phonon modes in the strongly correlated metal V2O3. Our results show an alternative up-conversion pathway for the optical control of Raman-active modes in solids mediated by terahertz-driven electronic excitation.
Towards more efficient and specific driving and probing of coherent phonon dynamics in solids
Boie, Larissa (2022)
Ultrafast spectroscopy is a powerful tool to study materials and their microscopic interactions in non-equilibrium states. With ultrafast methods, it is possible to reveal how electrons and atoms move and interact on very short timescales. Revealing the underlying mechanisms helps to understand how macroscopic phases form, which interaction channels are available and how to control materials with external stimuli to design specific properties. Depending on the type of interaction, the excitation energy for efficient coupling between the material and an external electric field comes from very different regions of the electro-magnetic spectrum. Nowadays, from x-rays to microwaves, powerful sources for most spectral ranges have been developed. They even cover the range from 0.3 THz to 30 THz (commonly referred to as the Terahertz gap), where the interaction of phonons – modes of lattice vibrations – with an external electric field can be studied directly. This has been difficult historically because this is the part of the spectrum where the radiation changes from electronic to photonic treatment. These sources are applied either as the pump or the probe pulse in an ultrafast pump–probe experiment. Inventions like the quantum cascade laser, the use of photoconducting antennas or the process of optical rectification in suitable nonlinear crystals now lead to sources of low frequencies. Pushing the development of sources in the meV energy range to higher stability, higher powers, and table-top setups to enhance possible excitation schemes for more advanced material control is still an ongoing challenge. Furthermore, the need for narrowband sources (the counterpart of the established broadband sources) has grown, enabling elaborate pump–probe schemes while minimizing energy losses. With narrowband sources, it is possible to study specific vibrations in solids and gases with high energy specificity. This work focuses on the excitation and detection of coherent phonons on ultrafast timescales. The need for high pulse intensities to excite phonons efficiently into a nonlinear regime calls for new pump and probe schemes. I refine two aspects of the recent developments: In the first part, I present the characterisation of a new high-power narrowband source in the far- to mid-infrared spectral regime. The narrowband characteristic is achieved by chirping two infrared (IR) pulses used in a difference frequency generation (DFG) process. Varying the applied amount of chirp in each IR beam allows for sensitive tuning of the frequency sweep over the duration of the mid-IR pulse. This opens up new excitation schemes, e.g. with the concept of capture into resonance. A flexible table-top setup with tunable center frequency and chirp will enhance the efficiency of phonon driving, making nonlinear excitation regimes accessible. With the extensive characterisation of the setup constructed during my thesis project we can tune the electric field properties precisely and identify the maximum tuning range and pulse parameters. This became possible by a comprehensive study on the influence of certain parameters on the amount of chirp of the obtained mid-IR pulse and by modelling the electric field with large qualitative agreement. In addition to the development of new pulsed sources, the capabilities of structure-sensitive probes have increased significantly, driven by the improvement of x-ray free electron lasers (XFELs). Reduced temporal jitter and enhanced brightness allow for detailed analysis even in complex materials, where vibrational signatures can be small. Sophisticated data treatment and advanced experimental techniques have enabled an increased understanding on electron–phonon coupling in complex materials. The second part investigates ultrafast x-ray diffraction in a prototypical quasi-1D charge-density-wave (CDW) material, the blue bronze K0.3MoO3. With x-rays as a structure-sensitive probe, we are able to distinguish atoms involved in the excitation of specific phonon modes. With the aid of a simulation for the structure factors of individually distorted atoms in the crystal structure, we can decompose the atomic motion associated with CDW phonon modes for the first time: An amplitude mode at 1.68 THz is directed mostly along the y axis, and a 2.5 THz phonon mode has its main contribution along the z axis. This analysis can help towards the understanding of electron–phonon coupling mechanisms, especially for materials with larger unit cells, where calculations are currently still infeasible.
Comparison of coherent phonon generation by electronic and ionic Raman scattering in LaAlO3
Neugebauer, Martin J.; Juraschek, Dominik M.; Savoini, Matteo; et al. (2021)
Physical Review Research
In ionic Raman scattering, infrared-active phonons mediate a scattering process that results in the creation or destruction of a Raman-active phonon. This mechanism relies on nonlinear interactions between phonons and has in recent years been associated with a variety of emergent lattice-driven phenomena in complex transition-metal oxides, but the underlying mechanism is often obscured by the presence of multiple coupled order parameters in play. Here, we use time-resolved spectroscopy to compare coherent phonons generated by ionic Raman scattering with those created by more conventional electronic Raman scattering on the nonmagnetic and non-strongly-correlated wide-band-gap insulator LaAlO3. We find that the oscillatory amplitude of the low-frequency Raman-active Eg mode exhibits a sharp peak when we tune our pump frequency into resonance with the high-frequency infrared-active Eu mode, consistent with first-principles calculations. Our results suggest that ionic Raman scattering can strongly dominate electronic Raman scattering in wide-band-gap insulating materials. We also see evidence of competing scattering channels at fluences above 28mJ/cm2 that alter the measured amplitude of the coherent phonon response.
Correlation between electronic and structural orders in 1T−TiSe2
Ueda, Hiroki; Porer, Michael; Mardegan, José R.L.; et al. (2021)
Physical Review Research
The correlation between electronic and crystal structures of 1T−TiSe2 in the charge-density wave (CDW) state is studied by x-ray diffraction in order to clarify basic properties in the CDW state, transport properties, and chirality. Three families of reflections are used to probe atomic displacements and the orbital asymmetry in Se. Two distinct onset temperatures are found: T_CDW and a lower T* indicative for an onset of Se out-of-plane atomic displacements. T* coincides with a DC resistivity maximum and the onset of the proposed gyrotropic (chiral) electronic structure. However, no indication for chirality is found. The relation between the atomic displacements and the transport properties is discussed in terms of Ti 3d and Se 4p states that only weakly couple to the CDW order.
Kinetics of a Phonon-Mediated Laser-Driven Structural Phase Transition in Sn2P2Se6
Kubli, Martin; Savoini, Matteo; Abreu, Elsa; et al. (2019)
Applied Sciences
We investigate the structural dynamics of the incommensurately modulated phase of Sn 2 P 2 Se 6 by means of time-resolved X-ray diffraction following excitation by an optical pump. Tracking the incommensurable distortion in the time domain enables us to identify the transport effects leading to a complete disappearance of the incommensurate phase over the course of 100 ns. These observations suggest that a thin surface layer of the high-temperature phase forms quickly after photo-excitation and then propagates into the material with a constant velocity of 3.7 m/s. Complementary static structural measurements reveal previously unreported higher-order satellite reflection in the incommensurate phase. These higher-order reflections are attributed to cubic vibrational terms in the Hamiltonian.
Strong modulation of carrier effective mass in WTe2 via coherent lattice manipulation
Soranzio, Davide; Savoini, Matteo; Beaud, Paul; et al. (2022)
npj 2D Materials and Applications
The layered transition-metal dichalcogenide WTe2 is characterized by distinctive transport and topological properties. These properties are largely determined by electronic states close to the Fermi level, specifically to electron and hole pockets in the Fermi sea. In principle, these states can be manipulated by changes to the crystal structure. The precise impact of particular structural changes on the electronic properties is a strong function of the specific nature of the atomic displacements. Here, we report on time-resolved X-ray diffraction and infrared reflectivity measurements of the coherent structural dynamics in WTe2 induced by femtosecond laser pulses excitation (central wavelength 800 nm), with emphasis on a quantitative description of both in-plane and out-of-plane vibrational modes. We estimate the magnitude of these motions, and calculate via density functional theory their effect on the electronic structure. Based on these results, we predict that phonons periodically modulate the effective mass of carriers in the electron and hole pockets up to 20%. This work opens up new opportunities for modulating the peculiar transport properties of WTe2 on short time scales.
Phase transition driven by ultrashort laser pulses in the charge-density-wave material K0.3MoO3
Winkler, Rafael; Boie, Larissa; Deng, Yiwei; et al. (2023)
Formation of phase inverted domains in the charge density material blue bronze
Winkler, Rafael; Boie, Larissa; Deng, Yunpei; et al. (2022)

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Larissa Boie

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