arXiv subjects

Torstein Hegstad

Publications and source records attributed to Torstein Hegstad.

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

Picosecond localization dynamics following ultrafast nanoscale magnetic switching

Ultrashort laser pulses provide the fastest known way to switch magnetic order. Such excitation commonly creates nanometer-scale domains, even after homogeneous illumination when the position of nucleated domains is not externally defined. However, the physics of domain localization during such ultrafast phase transitions remains unresolved. Here, we use shot-resolved pump-probe resonant x-ray scattering together with a material featuring a periodically modulated magnetic anisotropy landscape to track, in real time, the laser-driven nucleation and localization of nanometer-scale spin textures. We find that nucleation and localization are two distinct processes. Nucleation occurs homogeneously via fluctuations at early times, whereas spatially periodic structures emerge only later and, under suitable conditions, localize in less than one nanosecond. Real-space simulations show that this localization is governed by strong lateral variations in spin-texture lifetimes. Our results demonstrate that ultrafast phase-transition dynamics fundamentally differ from conventional transitions, yet still can be controlled through moderate nanometer-scale tailoring of the energy landscape.

cond-mat.mes-hall↗

arXiv2025

Ultrafast coherent magnon spin currents in antiferromagnets

Generating coherent magnon spin currents with the highest frequencies and shortest wavelengths is a key challenge in ultrafast spintronics and magnonics. A promising route is to excite counter-propagating magnon pairs. In antiferromagnets, such pairs can be accessed in the ultrafast regime, where coherent dynamics are dominated by magnons at the edge of the Brillouin zone. However, it has seemed impossible to generate a net spin current from coherent magnon pairs. Here we show that a coherent superposition of multiple magnon-pair modes can produce such a current in parity-time symmetric antiferromagnets. The ultrafast coherent spin currents are excited with linearly polarized light, with the light polarization steering the current direction. Finally, by superposing two orthogonal spin currents, circular spin currents can be generated, which have not been discussed for steady-state currents.

cond-mat.mes-hall↗