arXiv subjects

Martin Pavelka

Publications and source records attributed to Martin Pavelka.

3 recordsLinked to original sources

arXiv2026

Exciton-induced magnons carrying orbital angular momentum in CrI3

Magnons are collective spin excitations that contain and transport spin angular momentum in magnetic materials. It has been suggested that they can also carry orbital angular momentum in analogy to the electronic motion around the nucleus. We explore the real-space topology of magnon wave-packets emanating from atomic-like excitons in the ferromagnetic insulator CrI3 and demonstrate the existence of orbital angular momentum in such wave-packets. We reveal that orbital angular momentum of magnons is nearly equal to their spin angular momentum and compensates the latter. This illustrates the existence of an unexplored internal angular momentum balance and demonstrates that the magnetization can be quenched without the need of angular momentum exchange with the lattice.

cond-mat.mtrl-sci↗

arXiv2025

Femtosecond charge and spin dynamics in CoPt alloys

The use of advanced X-ray sources plays a key role in the study of dynamic processes in magnetically ordered materials. The progress in X-ray free electron lasers enables the direct and simultaneous observation of the femtosecond evolution of electron and spin systems through transient X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD), respectively. Such experiments allow us to resolve the response seen in the population of the spin-split valence states upon optical excitation. Here, we utilize circularly polarized ultrashort soft X-ray pulses from the new helical afterburner undulator at the free-electron laser FLASH in Hamburg to study the femtosecond dynamics of a laser-excited CoPt alloy at the Co $L_{3}$ absorption edge. Despite employing a weaker electronic excitation level we find a comparable demagnetization for the Co $3d$-states in CoPt compared to previous measurements on CoPd. This is attributed to distinctly different orbital hybridization and spin-orbit coupling between $3d$ and $4d$ vs. $3d$ and $5d$ elements in the corresponding alloys and multilayers.

cond-mat.mtrl-sci↗

arXiv2021

Strain Engineering of Epitaxial Pt/Fe Spintronic Terahertz Emitter

Spin-based terahertz (THz) emitters, utilizing the inverse spin Hall effect, are ultra-modern sources for the generation of THz electromagnetic radiation. To make a powerful emitter having large THz amplitude and bandwidth, fundamental understanding in terms of microscopic models is essential. This study reveals important factors to engineer the THz emission amplitude and bandwidth in epitaxial Pt/Fe emitters grown on MgO and MgAl$_2$O$_4$ (MAO) substrates, where the choice of the substrate plays an important role. The THz amplitude and bandwidth are affected by the induced strain in the Fe spin source layer. On the one hand, the THz electric field amplitude is found to be larger when Pt/Fe is grown on MgO even though the crystalline quality of the Fe film is superior when grown on MAO. This is because of the larger defect density, smaller electron relaxation time, and lower electrical conductivity in the THz regime when Fe is grown on MgO. On the other hand, the bandwidth is found to be larger for Pt/Fe grown on MAO and is explained by the uncoupled/coupled Lorentz oscillator models. This study provides an insightful pathway to further engineer metallic spintronic THz emitters in terms of the proper choice of substrate and microscopic properties of the emitter layers.

cond-mat.mtrl-sci↗