The physical response of condensed matter is determined by the microscopic interactions between internal degrees of freedom, such as charge, spin, or lattice. Ultrafast methods provide insights into these interactions by studying a materials ultrafast nonequilibrium response, which helps us to understand how macroscopic material properties arise from oftentimes complex microscopic...
Charged aqueous interfaces are the subject of extensive investigation due to their prevalence in both natural and industrial processes, with importance ranging across the biological, environmental, and chemical sciences. At such phase boundaries, the excess surface charge generates an electric field that penetrates through the electrolyte, perturbing the ion distributions and electric...
Liquid-vapor interfaces play a crucial role in the atmosphere. Their composition can alter compared to the bulk. We investigate complex acid-base equilibria, including tautomers and short-lived species, at the liquid-vapor interface with photoelectron spectroscopy.
The angular momentum of lattice vibrations — phonon angular momentum — is a largely unexplored degree of freedom in solid-state systems, playing a key role in the understanding of ultrafast demagnetization processes and offering new pathways for phonon-driven ultrafast material control, particularly relevant to spintronics and valleytronics. While this research area is rapidly growing, phonon...
The geometry of atoms in molecules and materials governs their properties. The controlled manipulation of their arrangement on the atomic scale is however limited with current technology.
This work explores non-contact atomic force microscopy (NC-AFM) as one possible tool to achieve this goal. Individual molecules of nonahelicene ([9]H) and coronene (Cor) are studied on a Ag(110)-surface and...
Cavity electrodynamics offers a unique avenue for tailoring ground-state material properties, excited-state engineering, and versatile control of quantum matter. Merging these concepts with high-field physics in the terahertz (THz) spectral range opens the door to explore low-energy, field-driven cavity electrodynamics, emerging from fundamental resonances or order parameters. Despite this...
*Tommaso Pincelli, Lawson T. Lloyd, Alessandro de Vita, Tania Mukherjee, Túlio de Castro, Amine Wahada, Roberto Sant$^a$, Srdjan Stavrič$^b$, Silvia Picozzi$^b$, Nathan P. Wilson$^c$, Zdeněk Sofer$^d$, Martin Wolf, Laurenz Rettig, Ralph Ernstorfer
$^a$Politecnico di Milano, Milano, Italy
$^b$Consiglio Nazionale delle Ricerche, Chieti, Italy
$^c$Walter Schottky Institute, Technische...
Surface phonon polaritons (SPhPs) are quasiparticles resulting from the hybridisation of IR photons with transverse optical phonons. The extreme light confinement, the low losses due to the long phonon lifetimes and the high directionality that can result from low crystal symmetries are among the factors that have made phonon polaritons so attractive to the nanophotonics community in the last...
Delving the rich dynamics of many-body quantum systems represents a profound challenge in both fundamental and applied science. This challenge arises due to the intricate correlation between carriers and nuclei, which entails complex dynamic processes occurring across timescales ranging from attoseconds to picoseconds. These processes include electronic and structural phase transitions, Mott...
Aqueous solution-vapor interfaces play a major role in atmospheric processes, for example in the interaction of the oceans or of aqueous aerosols with trace gases [1]. The largest contiguous aqueous-vapor interface is that of the oceans with air, covering more than 70% of the Earth’s surface [2]. Studies have shown that the ocean-air interface is covered by a thin film of amphiphilic...
1T-TaS$_2$ is a strongly correlated material characterized by a rich phase diagram
hosting a commensurate charge density wave (C-CDW) phase at low temperatures
accompanied by the opening of an insulating gap. These properties arise from the
interaction between electronic and lattice degrees of freedom, making 1T-TaS$_2$ a
prototype material for studying the complex quantum...
Antiferromagnetic (AF) spintronics is a promising route towards more efficient and stable devices, because antiferromagnets are less susceptible to external fields and foster a broad range of magnetic interactions with the potential for higher speeds and energy efficient manipulation. However, their self-cancelling magnetic moment makes the interaction with magnetic order challenging. One way...
Tommaso Pincelli, Lawson T. Lloyd, Amine Wahada, Zoè de Granrut, Alexander Enders, Tania Mukhejee, Túlio de Castro, Alessandro de Vita, Samuel Beaulieu, Maciej Dendzik, Shuo Dong, Holger Oertel, Martin Wolf, Laurenz Rettig, Ralph Ernstorfer.
We present our progress in developing the new paradigm of multidimensional photoemission spectroscopy (MPES) to probe quasiparticle wavefunctions. By...
Ultrathin ZnO on Ag(111) has emerged as an interesting material platform for the atomic-scale investigation of light-matter interaction in plasmonic tunnel junctions. As ultrathin layers, ZnO forms a two-dimensional hexagonal lattice with a layer-thickness dependent electronic structure. In addition, an interface state (IS) is formed at the ZnO/Ag(111) interface, whose coupling to the ZnO-CBE...
Hydrogen-bonded (H-bonded) molecular networks are ubiquitous in nature, appearing in systems such as DNA, proteins, and ice, to name a few. Achieving a comprehensive understanding of chemical reactions within these networks requires spatial resolution at the molecular level, which has been particularly challenging for photochemical studies. In this poster, we present our recent investigation...
Inhomogeneous molecular assemblies at interfaces play a critical role in both natural and industrial systems, with examples ranging from lipid rafts in biological membranes to lab-on-a-chip technologies. Investigating these assemblies at the molecular level, particularly their composition, arrangement, and packing structure, is a subject of great scientific interest. However, achieving such...
The air-water interface is one of the most prevalent interfaces on Earth and is central to a vast range of natural and industrial processes. The sheer presence of the interface induces significant changes in its properties such as density and dielectric function, as well as the distribution of molecular orientations and interconnectivity of the H-bond network. The widespread importance of...
Metal-halide perovskites (MHPs) emerged as exciting novel semiconductors with outstanding optoelectronic properties for applications in photovoltaics and light emission. More recently, these semiconductors also attract interest as promising candidates for spintronics. In the absence of inversion symmetry, spin-orbit coupling (SOC) leads to the Rashba-Dresselhaus effect, offering outlook for...
We report on tip-enhanced Raman spectroscopy (TERS) of H$_2$ and D$_2$ molecules physisorbed on Ag(111) at cryogenic temperatures (around 10 K). The intense Raman peaks resulting from the rotational and vibrational transitions are observed at sub-nanometer gap distances of the junction formed by a Ag tip and the Ag surface. Our results suggest that TERS based on low-temperature scanning...
Phonon polaritons are hybrid light-matter particles in solid-state materials that enable waveguiding of light on length scales much smaller than the photon wavelength. Here, we introduce HfSe$_2$ as a new van der Waals material that supports phonon polaritons in the terahertz (THz) spectral range. We image the propagation of these polaritons with a near-field optical microscope that is...
The Kagome lattice offers a plethora of interesting physics ranging from van-Hove singularities to Dirac points and flat bands. In particular, the Kagome metals family AV3Sb5 (A=K, Rb, Cs) features an unconventional superconducting phase, coexisting with a parent charge density wave (CDW) phase. The origin of the CDW is still under debate. Moreover, this family exhibit a flat band below the...
Femtosecond electron diffraction (FED) allows direct observation of a crystal lattice’s response to laser excitation. It is ideally suited to study the ultrafast energy flow from electrons to phonons as well as other photo-induced changes of the lattice, such as structural phase transitions, coherent phonons, and lattice distortions.
We have employed FED to probe lattice dynamics in 2d...
We present an ambient pressure X-ray photoelectron spectroscopy investigation of the adsorption of ammonia on ice over the temperature range of -23 °C to -50 °C. Previous flow tube studies showed significant uptake of ammonia at these temperatures to ice, which was linked to the incorporation of ammonium into the ice crystal lattice. Our present investigation shows a significant uptake of...
