The combination of nontrivial band topology & magnetism results in a wide variety of exotic electronic phases that -if realised at high temperatures- could revolutionise fields like spintronics or low-power consumption electronics. The new, second-generation ferrimagnetic compound Mn$_{1+x}$Sb$_{2-x}$Te$_4$ (0.1 ≤ x ≤ 1, abbreviated here as MST) promises to host the quantum anomalous Hall...
One of the limitations in exploiting the spin injection and transport properties of graphene is its strong electronic interaction with magnetic contacts. The π-states form complex and non-linear hybrid states when graphene is interfaced with 3d magnetic materials, such as Fe, Co, and Ni. Using density functional theory calculations and angle- and spin-resolved photoemission spectroscopy, I...
Large gap atomic quantum spin Hall insulators (QSHIs) grown epitaxially on SiC(0001) are promising candidates for spintronics at room temperature. The newly discovered QSHI indenene, a triangular monolayer of indium, exhibits a 120 meV gap and substrate-matched monodomainic growth yielding high quality films on the technologically relevant 𝜇m scale. Orbital interference on the lattice triangle...
The increasing interest in quantum technologies calls for purpose-designed nanoscale structures at surfaces. In my talk I will focus on tailored-made molecular structures that are made for two very different purposes: firstly, self-assembled molecular layers engineered for orbital cinematography, i.e., spatial and temporal imaging of electron dynamics in molecules at their intrinsic time...
The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked enormous research interest. However, despite the dedication of intensive experimental efforts and the proposal of several possible pairing mechanisms, the origin of its superconductivity remains elusive. Here, using angle-resolved photoemission spectroscopy with micrometer spatial...
Two-dimensional (2D) materials offer a versatile platform for exploring novel quantum phenomena and designing nanostructures with tailored functionalities. However, techniques such as photoemission spectroscopy, commonly used in 2D material studies, impose strict requirements for sample quality, uniformity, surface cleanliness, and size. Achieving these standards via traditional mechanical...
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...
High field THz-pulses allow accessing the Higgs mode, the amplitude mode of the order parameter, in superconductors. Using a phase-resolved THz-high-harmonics-spectroscopy we perform a complex Higgs-spectroscopy of the order parameter dynamics, symmetry and interaction with other collective modes [1,2]. In high-Tc cuprates and NbSe2 this allows investigating the interplay of charge density...
In the fields of optoelectronics and photochemistry, there is growing interest in studying the response to optical excitation of hybrid heterojunctions involving organic molecules. These systems are critical for developing the next generation of environmentally sustainable optoelectronic devices and catalysts. To investigate charge and lattice dynamics in hybrid heterojunctions at the...
Interplay of superconductivity and density wave orders has been at the forefront of research of correlated electronic phases for a long time. The balance between these two competing orders can be tuned by means of lattice deformation, i.e. pressure or strain. 2H-NbSe$_2$ is considered to be an ideal system for studying this interplay, but the origin of charge density wave in this material is...
We study the electronic structure of bulk 1T-TaSe$_2$ in the charge density wave (CDW) phase at low temperature. Our spatially and angle resolved photoemission (ARPES) data show insulating areas coexisting with metallic regions characterised by a chiral Fermi surface and weakly correlated low energy quasiparticle bands. Additionally, high-resolution laser ARPES reveals strong variations in the...
On the example of graphene, we will discuss various contributions to circular dichroism in angle-resolved photoemission (CD-ARPES) [1,2] which include phase shifts of the participating partial waves [3], the interatomic phase shifts [4], and the CD due to elastic scattering of an excited electron [5]. Multiple scattering calculations are performed using the EDAC cluster code [6] and the...
Flatband systems have attracted quite some interests due to their peculiar transport properties. The vanishing of the group velocity in the flatband makes the standard theory of transport not applicable. In recent years it has been shown that the underlying mechanism which allows transport in these system might be related to quantum geometric effects. In our work we study the transport through...
Recently, alloys and intermetallic compounds have gained significant attention due to their unique electronic and geometric structure, which are favourable for efficient catalytic applications. They offer promising alternatives to traditional monometallic catalysts, particularly in terms of cost, activity, stability, and selectivity. In this context, Ni-Ga bimetallic based catalysts...
Significant efforts in fundamental research have been dedicated to the study of two-dimensional metal-organic frameworks (2D MOFs) due to their potential in technological applications. These materials combine the structural flexibility of molecular systems with the ordered crystalline arrangement of solids. However, in metal-supported 2D MOFs, interactions with the substrate can significantly...
Topological superconductors are of great interest in the study of quantum materials due to their unique properties and potential applications in the fields like quantum computation and spintronics. Pd$_₃$Bi$_₂$Se$_₂$, a topological superconductor with a superconducting transition temperature of 0.80 K, is a promising candidate. Although it has been theoretically identified as a nontrivial...
We show first-principles calculations and angle- and spin- resolved photoemission spectroscopy studies of a two-dimensional bilayer of 𝛽-antimonene supported on bulk bismuth selenide. The trivial insulator 𝛽-antimonene inherits the topological surface state of the substrate as a result of the topological proximity effect. The new topological state exhibits an unusually high, almost complete...
The study of transient, far-from-equilibrium states in complex materials can offer profound insights into their microscopic properties, particularly when multiple observables are examined simultaneously. A central question in this field is whether atomic lattice displacements can be accurately tracked and controlled.
In this work, we investigate the ultrafast dynamics of Tellurium (Te) and...
The intrusion of transition metals (TMs) into two-dimensional (2D) layers of organic molecules self-assembled over metallic substrates significantly affects the properties of the resulting metal-organic frameworks (MOFs). A previous study demonstrated the impactful effect of Ni adsorption on the geometrical arrangement and electronic properties of a 1,2,4,5-tetracyanobenzene (TCNB) monolayer...
Charge-density-wave (CDW) materials, in which electrons and phonons cooperatively interact to form a new symmetry-broken state, stand as ideal candidates to study the mechanisms governing the melting of a macroscopically ordered phase. Furthermore, given their sensitivity to external stimuli, CDW materials constitute a promising platform to investigate the possibility of controlling their...
MXenes, the two-dimensional class of nanomaterials consisting of transition metal carbides, nitrides, or carbonitrides, have been spotlighted in the last decade due to their exceptional properties allowing them to be applicable in different fields. In particular, the Ti3C2Tx MXene phase has been paid a great deal of attention from the whole scientific community due to its unique...
Bi2Se3 belongs to a class of compounds known as tetradymites, is a well-known thermoelectric material that has also come into focus in recent years for its topological insulating properties. A three dimensional (3D) topological insulator (TI) is a material that is an insulator in the bulk and has metallic conductivity at the surface. The surface conductivity of TI arises from spin-orbit...
Tuning the electronic properties of a 2D crystal by the interaction with its support is the key to design well-controlled nanoelectronic devices based on transition metal dichalcogenides (TMDCs). In particular, the establishing of a low resistance between a metallic contact and the TMDC has been challenging and different strategies for this have been introduced. It was suggested that a low...
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 for...
Elettra 2.0 represents the latest evolution of Italy's third-generation synchrotron radiation facility, which has served scientific and industrial communities since 1993. Approved by the Italian Government in 2017, the Elettra 2.0 project involves replacing the current machine with a low-emittance storage ring, marking a significant milestone in synchrotron research. With enhanced brightness...
Kagome lattice is one of the most fertile geometric motifs in condensed matter physics, where a unique interplay between topology, correlation, and frustration gives rise to a plethora of quantum phenomena. Charge ordering is an example of quantum states prevalently observed in various Kagome lattice materials, including AV3Sb5, ScV6Sn6, and FeGe, and is found to be intertwined with...
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...
The wide family of 2D materials (2DMs) includes metals, semiconductors, superconductors, dielectrics, ferroics and more, each displaying novel phenomena due to the qualitatively different nature of interactions in 2D. However, the real delight is in the ability to combine different 2D materials into atomically defined heterostructures by simply stacking layers, engineering interactions between...
The study of chiral crystals is one of the frontiers in the field of topological materials. Weyl fermions with unique properties emerge in the absence of inversion and mirror symmetries [1]. Kramers-Weyl fermions, for example, are pinned at different high-symmetry points and surface arcs can connect them spanning over the entire Brillouin zone [2 - 4]. The physics of chiral crystals is further...
Surface experimental probes, such as angle-resolved photoelectron spectroscopy provide researchers access to the electronic structure of solids. Despite the advances in the field, recently, new forms of surface local magnetism completely different from standard descriptions have appeared. One example of such forms of magnetism are the one generated by the so-called loop currents, generated by...
During the past four years, I had the opportunity to participate in and contribute to the development of new techniques that expand the capabilities of the DiProI beamline at the FERMI free-electron laser (FEL) source. In particular, I will present a few results related (i) to the properties of light beams possessing orbital angular momentum (OAM) and (ii) to the magnetic dynamics triggered by...
