Dynamics of Correlated Materials
Dynamics of Correlated Materials
Emmy Noether Group Laurenz Rettig
Emmy Noether Group Laurenz Rettig


Welcome to the Dynamics of Correlated Materials group!

    We are an experimental research group focusing on the investigation of ultrafast processes in strongly correlated materials. Our goal is the understanding of the fundamental interactions at play on the microscopic level in such materials, leading to complex behavior. We develop and employ complementary ultrafast techniques such as time- and angle-resolved photoelectron spectroscopy (trARPES) and time-resolved diffraction techniques to study those elementary interaction processes and couplings across ultrafast phase transitions.




    New Preprint: Observation of interfacial Meitner-Auger energy transfer
    Aug 2021
    Interlayer charge- and energy transfer processes in atomically thin, layered van der Waals heterostructures are of fundamental importance for determining their properties in novel device concepts based on single active crystalline layers. In our recent preprint (arXiv link) we study the ultrafast excitation, relaxation and transfer processes in an epitaxial grown monolayer WSe2/graphene heterostructure using time- and angle-resolved photoemission spectroscopy. By measuring the non-equilibrium electronic structure, we identify a novel interfacial energy transfer mechanism: Meitner-Auger energy transfer, which describes the conversion of an exciton in the semiconductor to an intraband electron-hole pair in graphene, characterized by the excitation of deep-lying valence holes [more...]
    Paper Published: Nonequilibrium Charge-Density-Wave Order Beyond the Thermal Limit
    May 2021
    Phase transitions under quasi-equilibrium conditions, e.g., induced by a slow variation of temperature, are well described by Landau theory. In contrast, the situation far from equilibrium, e.g., after ultrafast laser excitation, differs fundamentally from a thermodynamic scenario, and it remains an open question how our understanding of static phase transitions in complex matter has to be adapted to capture a dynamical, photoinduced melting and recovery of order. In particular, even the thermal critical temperature might not provide a valid description in a system exhibiting strong non-equilibrium between different degrees of freedom, such as electrons and lattice.
    In our study which was published in Nature Communications, we investigate an ultrafast charge-density-wave-to-metal transition after optical excitation by combining state-of-the-art time-resolved electronic and structural [more...]
    New paper: Ultrafast modulation of a material's Fermi surface topology
    Apr 2021
    The transport of electrons is governed by the shape of the Fermi surface. We found that the topology of the Fermi surface of a semimetal can be manipulated on ultrafast timescales through optical excitation. A change in the Fermi surface topology, also called Lifshitz transition, can lead to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. Combining time-resolved multidimensional photoemission spectroscopy and TDDFT+U simulations, we introduce a scheme for driving an ultrafast Lifshitz transition in the correlated type-II Weyl semimetal Td-MoTe2. We show that this non-equilibrium topological transition finds its microscopic origin in the dynamical modification of the electronic correlations.
    Beaulieu et al., Science Advances 7, eabd9275 (2021). Link [more...]
    A link between exchange striction and nonthermal Lattice Dynamics
    Apr 2021
    Our recent study of ultrafast lattice dynamics in NiO has demonstrated the existance of a nonthermal phonon population, and that this is directly linked to change in the antiferromagnetically-induced lattice distortion, known as “exchange striction”. The study was enabled by combining unique capabilities of two institutions: growth of a 20nm-thick free-standing NiO single crystal at the university of Halle, and state-of-the-art femtosecond electron diffraction at the Fritz Haber Instititue. The study open a new avenue towards ultrafast control of antiferromagnets via the crystal lattice.
    Windsor et al, Phys. Rev. Lett. 126, 147202 (2021)
    New preprint: Bloch Wavefunction Reconstruction using Multidimensional Photoemission Spectroscopy
    Mar 2021
    The most advanced experimental technique to measure the electronic band structure of solids is angle-resolved photoemission spectroscopy (ARPES). While ARPES directly maps the momentum-resolved electronic eigenvalues (energy bands), topological properties are often hidden in the complex-valued Bloch wavefunction, which is not directly accessible in standard photoemission experiments. In a recent joint experimental and theoretical work in collaboration with Dr. Michael Schüler and Prof. Thomas Devereaux from Stanford University, we have found a novel approach to reconstruct the Bloch wavefunction of WSe2 from polarization-modulated ARPES, with minimal theory input (arXiv:2103.17168).