X-ray Free electron lasers (XFELs) produce intense coherent femtosecond pulses in a large energy range, extending the capabilities of laser-based sources. The soft X-ray regime is of paramount importance since it allows resonant studies of many materials with prospective technological applications. Photon-in/photon-out techniques at XFELs have been successfully implemented to study ultrafast...
The interaction of light beams with magnetic materials defines the rich set of analytical tools in magneto-optics, covering photon energies from infra-red to hard x-rays. In addition to the spin angular momentum (SAM) associated to the light polarization, Laguerre-Gaussian (LG) beams carry also an orbital angular momentum (OAM) of ℓℏ/photon [1] associated to an azimuthal dependence exp(iℓϕ) of...
Collective dynamics at the nanoscale in condensed matter is important for advancing both fundamental science and modern technology. The study of heat transport processes, vibrational modes or magnetization dynamics in the sub-100 nm length-scales can greatly benefit from the development of experimental tools for probing such dynamics and on the relevant timescale (i.e. ps and sub-ps) without...
A well-known problem of FELs is the shot-to-shot instability of several parameters of the XUV pulses, which is usually mitigated with single-shot diagnostics and data sorting in post-processing, based on the available metadata. When such data sorting is crucial, the verification on the outcome of the experiment can be sensitively delayed with respect to the data acquisition, so that potential...
The electronic and structural modifications occurring in photocatalysts after photoexcitation largely determine the light-induced functionality of such materials. Cerium oxide is a relevant catalyst with enhanced redox properties, due to its ability to easily and reversibly release oxygen atoms from its lattice.
In a pump-probe optical spectroscopy experiment on cerium oxide films we...
Black phosphorus is a unique two-dimensional (2D) material with a tunable infrared band gap and anisotropic conduction properties. We investigate the ambient pressure nonlinear terahertz (THz) electrodynamics of black phosphorus and found that its THz saturable-absorption properties can be understood within a thermodynamic model by assuming a fast thermalization of the electron bath. While...
The analysis of the polarization status of electromagnetic waves is fundamental for a large number of fields of research and technological applications. Intense magnetic fields modify the polarization of the emitted thermal radiation in white dwarf stars. Atomic displacements in solids -phonons- can be detected by Raman scattering with the use of light polarization analysis. Magnetic layers,...
The manipulation of the magnetization is essential for our society as it is applied in transformers, radio frequency components and data storage media. Magnetic random access memory (MRAM) devices may combine the advantages of static RAM and flash memory as it is fast and non-volatile. In MRAM a spin current is used to read and write the state of the memory cells. Therefore, it is one of the...
The development of quantum simulators, artificial platforms where the predictions of many-body theories of correlated quantum materials can be tested in a controllable and tunable way, is one of the main challenges of condensed matter physics. Here we introduce artificial lattices made of lead halide perovskite nanocubes as a new platform to simulate and investigate the physics of correlated...
The CeSb magnetic phase diagram contains at least 16 different magnetic phases in the H-T plane [1] comprising different sequences of ferromagnetic and paramagnetic (001) planes stacked along the c-axis. The complexity is thought to arise from the interplay of Kondo, spin-orbit and crystal-field effects. [1, 2] Lattice modulation in the magnetic phases was also observed [3].
The phase diagram...
MoS2 belongs to the class of graphene-like, layered materials called transition metal dichalcogenides (TMDs). Semiconducting TMDs, like MoS2, show an indirect to direct bandgap transition when the system is exfoliated down to the monolayer structure, which makes them promising materials for future applications in optoelectronics and related fields [1]. Unravelling the relaxation pathways of...
Long-range electronic order descending from a metallic parent state constitutes a rich playground to study the intricate interplay of structural and electronic degrees of freedom. Kagome materials appeared as the perfect stage for such explorations. Specifically, RV6Sn6 (R = rare earth atom) bilayer kagome metals are topological systems with Dirac-like itinerant states, van Hove singularities...
Two dimensional (2D) transition metal dichalcogenides (TMDs) have received increasing attention because of their optical and electronic properties, including enhanced light-matter interaction, strongly bound excitons, exciton Rydberg states, multiparticle excitonic complexes, and valley-selective circular dichroism [1]. Some of these properties are exploited in the realization of prototypical...
Hybrid quasi-particles in condensed matter systems are observed at the degeneracy points between different degrees of freedom exhibiting non-zero coupling. These solid-state chimeras could be exploited in a wealth of applications, from transducers to sensors, to memory and logic units [1]. In particular, magneto-elastic coupling allows for efficient magnon-phonon hybridization in the few...
Hybrid-polaritons are energy states obtained from the strong coupling between matter excitons and optically confined photons [1]. In case of donor-acceptor microcavity system, when both excitons are coupled with the same cavity mode three polariton states are formed. Such states are named: Upper Polariton Branch (UPB) energetically higher with respect to the donor exciton, Lower Polariton...
The interaction of very short and intense laser pulses with noble gases generates high-order harmonics, which creates coherent Extreme UltraViolet (EUV) and Soft-X Ray radiation on a tabletop scale. This allows ultrafast spectroscopy to achieve extreme temporal resolutions, reaching the attosecond level, and site and chemical selectivity. These unique features enable the observation of...
*Thomas Vasileiadis, Shuo Dong, Samuel Beaulieu, Maciej Dendzik, Daniela Zahn, Sang-Eun Lee, Hélène Seiler, Yinpeng Qi, Rui Patrick Xian, Julian Maklar (Fritz-Haber-Institut der MPG, Berlin, Germany), Michael Schüler (Paul Scherrer Institut, Villigen, Switzerland), Emerson Coy (NanoBioMedical Centre, Adam Mickiewicz University, Poznan, Poland), Niclas S. Mueller, Yu Okamura, Stephanie Reich...
The wealth of information that is encoded in the spectra of core level photoelectrons, like binding energies, line shapes, and diffraction-induced intensity modulations, makes this type of spectroscopy an attractive tool for the study of out-of-equilibrium quantum materials.
Ultrafast structural manipulation can for example manifest hidden or metastable phases. Time-resolved core-level...
Complex materials encompassing different phases of matter can display new photoinduced metastable states differing from those attainable under equilibrium conditions.
These states can be realized when energy is injected in the material following a non-equilibrium pathway, unbalancing the unperturbed energy landscape of the material.
Guided by the fact that photoemission experiments allow...
Comprehension of anisotropic materials is crucial for developing polarization-sensitive photodetectors and polarizers [1]. Binary II-V semiconductors are among the most promising candidates to reach this goal, exhibiting anisotropic optical and electronic responses [2]. As a part of this family, ZnAs2 has an energy absorption edge that varies by more than 30 meV when light polarization is...
Coherent light matter interaction plays a pivotal role in future quantum technologies. The dephasing of electronic excitations in condensed matter system proceed on ultrashort time scales due to microscopy many body interactions and can only be indirectly measured by linear spectroscopies, whereas nonlinear optical methods do no provide momentum resolution. In this talk I will discuss ARPES...
In the attosecond molecular dynamics community, there is great interest in the development of light sources capable of producing tunable ultraviolet (UV) pulses with few femtoseconds duration. Indeed, the ability to excite resonantly (usually in the UV range) allows one to study the electronic processes of molecules in their neutral state, i.e., without ionizing it. Big strides in this...
The coexistence of strong electron-phonon coupling and non-trivial topological physics in quantum materials can lead to new exciting phenomena, and the study of the interplay of these multiple quantum orders constitute a new paradigm in condensed matter. Here, by combining time and angle-resolved photoemission spectroscopy (TR-ARPES) and broadband time resolved optical spectroscopy (TR-OS), we...
Among the materials hosting Charge Density Wave (CDW) phases, transition metal tri-chalcogenides have attracted considerable attention thanks to their quasi-one-dimensional (1D) nature. ZrTe3 is of particular interest because its Fermi surface comprises both a 3D hole like pocket centered at $\Gamma$ and quasi 1D bands at the zone edges [1,2]. Extensive ARPES studies have shown that the CDW...
Chirality has emerged as a trend topic in condensed matter, as it enforces special symmetries in collective excitations [1, 2] and magnetic ordering [3] and it is responsible for novel quasiparticles beyond Dirac, Weyl and Majorana fermions [4]. The physics of chiral crystals is further enriched by the unique spin arrangements in momentum space [5], by non-linear optical and transport...
The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the ultrafast dynamical control and creation of novel ordered states of matter, not accessible in thermodynamic equilibrium, is receiving much attention. Among those, the theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of...
The appearance of hot-phonons states in pump-probe experiments as a powerful tool for characterizing the time-dynamics of the energy flows, as well in perspective of engineering on/off switchs based on the lattice degrees of freedom and for heat transport. While these features were initially thought to be specific of semiconductors, hot-phonons has been recently predicted and observed as well...
Magnons, which are quanta of magnetic excitations, have been extensively studied due to their importance in both fundamental research and technological applications. Specifically, magnons with frequencies in the GHz range are of particular interest as they are utilized in modern communication systems. Here, we introduce a novel all-optical method for exciting magnons in the GHz range with...
We investigated by means of the ultrafast time-resolved magneto-optical Kerr effect (MOKE) spectroscopy [1] the effect of the interface between organic molecular semiconductors and cobalt on the magnetic anisotropy of polycrystalline Co thin films. Comparison of the effect was measured on interfaces of Co with: nonmagnetic metal (Al), metalorganic complexes tris(8-hydroxyquinoline)gallium...
We employed the time-resolved magneto-optical setup described in [1] to study the optically driven lattice and spin dynamics of a 380 nm thick exfoliated flake of the antiferromagnetic van der Waals semiconductor FePS$_3$ as a function of excitation photon energy, sample temperature and external magnetic field [2]. We found evidence of a coherent optical lattice mode with a frequency of 3.2...
With its direct correspondence to the electronic structure, angle-resolved photoemission spectroscopy (ARPES) is a ubiquitous tool for the study of quantum materials. When ex-tended to the temporal domain, time-resolved ARPES offers the potential to move beyond equilibrium properties, exploring both the unoccupied electronic structure as well as its dy-namical response under ultrafast...
