MPSD Exchange

Interfaces between different material phases or materials of different chemical composition often define or allow tuning the properties of a system of interest. An atomistic level of understanding such interfaces provides an invaluable insight into the electronic properties and microscopic mechanisms that lead to interfacial reactions, atomic restructuring, and emergent electronic properties. In the first part of this seminar, I will introduce several fundamental concepts of the methodology our group uses in its research, such as the Born—Oppenheimer approximation for the dynamics of nuclei and the notion of the first-principles potential energy surface, the efficient and rigorous treatment of nuclear quantum effects via the imaginary-time path-integral formulation, and the representation of first-principles electronic structure by machine learning models. I will then discuss in more detail how one can connect to experiments by using such simulations, in particular regarding the simulation of Raman scattering signals. I will discuss our developments of first-principles simulations of tip-enhanced Raman spectroscopy (TERS) images of molecular adsorbates on metal substrates. The results demonstrate that accurate simulations are capable of reproducing experimental measurements and serve as a powerful interpretative tool that allows us to shed light on the role of the metal substrate in shaping TERS images and discuss the underlying physics. To reach beyond the harmonic approximation, we demonstrate that the methods of molecular dynamics and machine learning can be seamlessly integrated into the TERS simulations and enable efficient, large-scale, quantitative predictions of nuclear quantum and finite-temperature effects on such spectra. [more]

Surface Acoustic Waves (SAWs) are directed phonon modes whose amplitude, wavelength, andfrequency can be precisely controlled via nanofabrication techniques. From transportmeasurements in 2D quantum materials to optical spectroscopy, SAWs represent a tool forexploring and manipulating light-matter-phonon coupling in low-dimensional condensed mattersystems.This talk will introduce the fundamental concept of SAW generation and propagation,highlighting how piezoelectric transduction enables coherent phonon control. We will showcaseopportunities for interdisciplinary collaboration across the Max Planck Institute for the Structureand Dynamics of Matter, where SAW technology bridges multiple experimental domains:modeling phonon-driven dynamics and strain-engineered band structures, optical spectroscopyof SAW-induced modulation in 2D materials, and tailored microfabrication for ultra-shortwavelength devices. [more]

When an intense laser is emitted on a solid, the material can emit light at many multiples of the laser’s color, so‑called high harmonics. These harmonics act like fingerprints of how electrons move and interact on an extremely short timescale. We review recent theoretical advances for describing the all-optical spectroscopic technique of high-order harmonic spectroscopy in condensed matter systems. Theoretical methods for characterizing the underlying ultrafast electron processes, their interactions beyond the electric dipole, and the presence of excitons will be discussed. With it, predictions are made concerning the spectroscopic signatures of beyond-electric-dipole interactions, exciton processes, phase transitions, or other aspects of the ultrafast generation process. [more]

UTe2 displays a tantalizing phase diagram under high magnetic fields, featuring multipleunconventional superconducting and magnetic phases with distinct order parameters. In thisMPSD exchange seminar, I will present our recent experimental results on probing nonlinearelectronic transport in these non-trivial states.First, I will discuss the field-reinforced superconducting state and its strongly anisotropic vortexresponse with respect to both current and magnetic-field orientation. These results reveal anunexpected quasi-2D superconducting state in a non-layered material. Next, I will provideevidence for a first-order transition modulated by high current densities in the high-field region,emphasizing its direct connection to a hidden order within the field-polarized phase. [more]

Chirality is a fundamental symmetry property of materials. Beyond the conventional classification of crystal systems as chiral or achiral, there exists a distinct subclass of achiral systems known as antiferrochiral. In this kick-off seminar of the MPSD internal seminar series, I will discuss the novel properties of such systems, including linear and nonlinear responses, as well as quasiparticle excitations.The concept of higher-order chirality will be introduced as a unified framework to describe these systems. Building on this perspective, new opportunities for chirality engineering will be highlighted, focusing on two recent experimental demonstrations from the Cavalleri department: light control of chirality and strain control of chirality. [more]