arXiv subjects

Gian Parusa

Publications and source records attributed to Gian Parusa.

3 recordsLinked to original sources

arXiv2026

Hierarchical quasiparticle dynamics in antiferromagnets revealed by time- and momentum-resolved X-ray scattering

Energy flows among coupled subsystems are essential for ultrafast dynamics and high-speed technologies. In magnetic materials, spin fluctuations -- magnons -- mediate these flows in ultrafast magnetism. Yet momentum-resolved access to low-energy magnons governing the microscopic dynamics has been lacking. Using time-resolved resonant diffuse scattering alongside complementary time-resolved X-ray techniques and quantum-kinetic simulations, we unveil the hierarchical energy pathways among correlated systems in the photoexcited antiferromagnet CuO. Above-bandgap excitation triggers near-instantaneous spin disorder, generating non-thermal magnons throughout reciprocal space within femtoseconds. Real-time momentum-resolved tracking reveals picosecond magnon quasi-thermalization, followed by nanosecond recovery via momentum-selective magnon-phonon scattering. The quasiparticle dispersion mismatch creates recovery bottlenecks that control non-equilibrium lifetimes. This microscopic framework transcends phenomenological models and generalizes across materials, establishing design principles for ultrafast control of material properties.

cond-mat.str-el↗

arXiv2026

Accurate and efficient simulation of photoemission spectroscopy via Kohn-Sham scattering states

We introduce an efficient first-principles framework for simulating angle-resolved photoemission spectroscopy (ARPES) based on the direct computation of photoelectron states as solutions of the Kohn-Sham equation with scattering boundary conditions. While the one-step theory of photoemission has a long and successful history, existing implementations are often tied to specialized electronic-structure formalisms. Our approach is formally equivalent to the Lippmann-Schwinger formulation, and it is directly compatible with standard plane-wave and real-space density functional theory codes, enabling seamless integration with advanced exchange-correlation functionals and modern electronic-structure workflows. By providing explicit photoelectron wave functions, the method allows for a transparent analysis of matrix-element effects, multiple scattering, and experimental geometry. We demonstrate the accuracy and predictive power of the framework through circular-dichroism ARPES simulations for monolayer graphene and bulk $2H$-WSe$_2$, achieving excellent agreement with experimental data over a wide photon-energy range. Our results establish a robust and accessible route toward quantitative ARPES modeling, opening the door to systematic studies of orbital textures, many-body effects, and nonequilibrium phenomena within widely used ab initio platforms.

cond-mat.mtrl-sci↗

arXiv2024

First-principle tight-binding approach to angle-resolved photoemission spectroscopy simulations: importance of light-matter gauge and ubiquitous interference effects

Angle-resolved photoemission spectroscopy (ARPES) is one of the most powerful techniques to study the electronic structure of materials. To go beyond the paradigm of band mapping and extract aspects of the Bloch wave-functions, the intricate interplay of experimental geometry, crystal structure, and photon polarization needs to be understood. In this work we discuss several model approaches to computing ARPES signals in a unified fashion. While we represent the Bloch wave-functions by first-principle Wannier functions, we introduce different approximations to the final states and discuss the implications for the predictive power. We also introduce various light-matter gauges and explain the role of the inevitable breaking of gauge invariance.Finally, we benchmark the different models for the two-dimensional semiconductor WSe$_2$, known for its strong Berry curvature, orbital angular momentum (OAM), and nontrivial orbital texture. The models are compared based on their ability to simulate photoemission intensity and interpret circular dichroism in ARPES (CD-ARPES). We show that interference effects are crucial to understanding the circular dichroism, and explain their photon-energy dependence. Our in-depth analysis provides insights into the advantages and limitations of various model approaches in clarifying the complex interplay between experimental observables and underlying orbital texture in materials.

cond-mat.mtrl-sci↗