arXiv subjects

Eva Paprotzki

Publications and source records attributed to Eva Paprotzki.

5 recordsLinked to original sources

arXiv2026

Floquet X-Ray Scattering as a Probe of Hidden Electronic Orders

We develop a theoretical framework for Floquet resonant X-ray scattering, using Floquet theory combined with the ultrashort core-hole lifetime expansion. We obtain a compact expression for the Floquet components of the resonant inelastic X-ray scattering operator, which shows that Floquet X-ray scattering provides direct access to bond and current correlations that do not directly produce charge Bragg peaks in conventional diffraction. Applying this framework to charge-ordered states on the Kagome lattice, we demonstrate that different symmetry-breaking orders exhibit distinct polarization fingerprints in the Floquet Bragg peaks. Moreover, the relative weight of bond and current contributions can be tuned through the drive frequency. These results establish Floquet X-ray scattering as a symmetry-resolved probe of hidden electronic order or fluctuations in quantum materials.

cond-mat.str-el↗

arXiv2025

High order strong-coupling expansion for X-ray absorption on a dynamically screened impurity

Time-resolved X-ray absorption can reveal the dynamical screening of the local Coulomb interaction in strongly correlated photo-excited materials. Here, we focus on the theoretical prediction of X-ray absorption in the presence of dynamical screening using the strong coupling expansion, i.e., an expansion around the isolated absorption site in terms of the retarded interaction. The evaluation of higher order diagrams is made numerically feasible by an approach based on the decomposition of the retarded interaction into complex exponentials. With this, we evaluate the strong coupling series to third order on an electron-boson model of Holstein type. We demonstrate that in relevant coupling regimes, even low orders of the strong coupling expansion can give a significant correction over the previously used lowest order approximation.

cond-mat.str-el↗

arXiv2024

Measuring the ultrafast screening of $U$ in photo-excited charge-transfer insulators with time-resolved X-ray absorption spectroscopy

Recent seminal experiments have utilized time-resolved X-ray absorption spectroscopy (XAS) to investigate the ultrafast photo-induced renormalization of the electron interaction (''Hubbard $U$'') in Mott and charge transfer insulators. In this paper, we analyze the change of interactions due to dynamical screening as it is encoded in the XAS signal, using the non-equilibrium GW+EDMFT formalism. Our study shows that XAS is well-suited for measuring this change, but two aspects should be kept in mind if the screening processes are not substantially faster than the valence electron dynamics: (i) Screening in a photo-excited system can affect both the position and the lineshape of the absorption lines. (ii) In general, the effect cannot be captured by the modification of a single interaction parameter. Specifically, an estimate for $ΔU$ extracted from the shift of the XAS lines does not necessarily describe the related shift of the the upper Hubbard band. We clarify these aspects using a minimal cluster model and the three-band Emery model for a charge transfer insulator.

cond-mat.str-el↗

arXiv2024

Quench dynamics in higher-dimensional Holstein models: Insights from Truncated Wigner Approaches

Charge-density wave phases in quantum materials stem from the complex interplay of electronic and lattice degrees of freedom. Nowadays, various time-resolved spectroscopy techniques allow to actively manipulate such phases and monitor their dynamics in real time. Modeling such nonequilibrium dynamics theoretically is a great challenge and exact methods can usually only treat a small number of atoms and finitely many phonons. We approach the melting of charge-density waves in a Holstein model after a sudden switch-on of the electronic hopping from two perspectives: We prove that in the non-interacting and in the strong-coupling limit, the CDW order parameter on high-dimensional hypercubic lattices obeys a factorization relation for long times, such that its dynamics can be reduced to the one-dimensional case. Secondly, we present numerical results from semiclassical techniques based on the Truncated Wigner Approximation for two spatial dimensions. A comparison with exact data obtained for a Holstein chain shows that a semiclassical treatment of both the electrons and phonons is required in order to correctly describe the phononic dynamics. This is confirmed, in addition, for a quench in the electron-phonon coupling strength.

cond-mat.str-el↗

arXiv2020

From entropic to energetic barriers in glassy dynamics: The Barrat-Mézard trap model on sparse networks

Trap models describe glassy dynamics as a stochastic process on a network of configurations representing local energy minima. We study within this class the paradigmatic Barrat-Mézard model, which has Glauber transition rates. Our focus is on the effects of the network connectivity, where we go beyond the usual mean field (fully connected) approximation and consider sparse networks, specifically random regular graphs. We obtain the spectral density of relaxation rates of the master operator using the cavity method, revealing very rich behaviour as a function of network connectivity $c$ and temperature $T$. We trace this back to a crossover from initially entropic barriers, resulting from a paucity of downhill directions, to energy barriers that govern the escape from local minima at long times. The insights gained are used to rationalize the relaxation of the energy after a quench from high $T$, as well as the corresponding correlation and persistence functions.

cond-mat.dis-nn↗