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Ultrafast optical excitation is widely used to manipulate electronic and magnetic properties of materials on femtosecond timescales. In this study, we investigate the response of copper to circularly polarized femtosecond pulses using time-resolved magneto-optical Kerr effect measurements. We compare the dynamics induced by single-pulse excitation with those resulting from a dual-pump configuration, in which two pulses arrive simultaneously from different directions. Although the individual contributions of the two pumps are similar when applied separately, their combined effect leads to a marked change in the spin/orbital dynamics. Specifically, we observe an approximately 2.5-fold increase in the decay time of the spin/orbital imbalance signal under dual-pump excitation. This result indicates that the joint action of two optical pulses can qualitatively alter the relaxation pathways in the system, beyond a simple additive response. The observed behavior highlights a previously unexplored regime of light-induced dynamics and suggests new strategies for controlling ultrafast processes in solids.

Ultrafast control of lattice motion in metals is a central challenge for high-frequency strain engineering and spintronic applications. Coherent strain control at terahertz (THz) frequencies in metals has remained elusive because free electrons are expected to delocalize energy beyond the optical penetration depth, preventing rapid and efficient stress generation. Here we show that robust and cost-effective metal-metal superlattices (SLs), where periodic repetitions of bilayers - each layer a few atoms thick - are deposited by sputtering, constitute thermoacoustic metamaterials that overcome this limitation. We combine femtosecond X-ray diffraction with mode-resolved density-functional theory and two-temperature modeling to show that electron pressure, rather than phonon stress, drives a large-amplitude coherent terahertz (1 THz) lattice oscillation in sputtered Pt/Cu superlattices. We establish electron pressure as an engineerable, dominant actuation mechanism in metallic metamaterials which can be tailored by the pitch and the constituent materials of the sputtered SL structure, enabling applications such as ultrafast strain-mediated antiferromagnetic spintronic devices.

The ultrafast magnetization dynamics of an epitaxial Fe/CoObilayer on Ag(001) is examined in an element-resolved way by resonant soft-x-ray reflectivity. The transient magnetic linear dichroism at the Co 𝐿₂ edge and the magnetic circular dichroism at the Fe 𝐿₃ edge measured in reflection in a pump–probe experiment with 120 fs temporal resolution show the loss of antiferromagnetic and ferromagnetic order in CoO and Fe, respectively, both within 300 fs after excitation with 60 fs light pulses of 800 and 400 nm wavelengths. A comparison to spin-dynamics simulations using an atomistic spin model shows that direct energy transfer from the laser-excited electrons in Fe to the magnetic moments in CoO provides the dominant demagnetization channel in the case of 800-nm excitation.

The electrical generation of orbital angular momentum in materials has attracted significant attention due to its fundamental importance and technological potential. Notably, recent experiments on orbital torque and terahertz emission suggest that Cu enables substantial charge-to-orbital interconversion upon oxidation. However, direct evidence of orbital generation in Cu remains elusive. In this work, we demonstrate current-induced orbital accumulation in pristine and naturally oxidized Cu films using magneto-optical Kerr effect measurements. We observe distinct thickness dependences of the Kerr signals in pristine and oxidized films, revealing bulk- and interface-driven orbital generation mechanisms corresponding to the orbital Hall effect and orbital Rashba-Edelstein effect, respectively. The extracted orbital diffusion length in Cu is significantly shorter than its known spin diffusion length, yet still exceeds atomic scales. These findings provide clear evidence of orbital generation in Cu and highlight the distinct bulk and interfacial mechanisms underlying it.

Rotating magnon wave packets carrying orbital moments offer a pathway to unconventional transport phenomena. Here, we investigate magnon orbital moments and the magnon orbital Nernst effect in the prototypical altermagnets RuO2 and CrSb using first-principles calculations, linear response theory, and symmetry analysis. While symmetry constraints enforce vanishing equilibrium magnon orbital moments, we find that in thermal non-equilibrium a finite and robust magnon orbital Nernst effect emerges from the anisotropic Heisenberg exchange, regardless of spin-orbit coupling. This effect is intrinsically tied to the unique exchange splitting of magnon dispersions in altermagnets and is absent in conventional antiferromagnets. Magnon orbital moment transport displays markedly reduced sensitivity to the orientation of the N & eacute;el vector, temperature gradient, and magnetic domain structure compared to the magnon spin Seebeck and spin Nernst effects, enabling its persistence even in polycrystalline samples with arbitrary domain configurations. Our results position magnon orbital transport as a promising and robust functional mechanism for orbitronic and spintronic devices, and as a potential indirect probe of altermagnetism in disordered insulating systems.

Altermagnets host unconventional spin-polarized bands despite zero net magnetization, but controlling their spin structure remains challenging. We theoretically propose a multifield approach to engineer spin polarization in 𝑑-wave altermagnets using gating, optical driving, and in-plane electric fields, which enable tunable and switchable polarizations along multiple directions. Optical driving induces out-of-plane (𝑧) polarization, while gating and in-plane fields generate 𝑥 and 𝑦 polarizations via the Edelstein effect, all of which are experimentally detectable. We further find that spin- and band-selective doping induces chiral optical activity, a feature unique to altermagnets. Our approach offers a versatile means to control the direction of spin polarization in altermagnets.

The manipulation of magnetization in ferromagnetic metals (FMs) through orbital torque (OT) has emerged as a promising route for energy-efficient magnetic devices without relying on heavy metals. While Ti and Cu are among the most extensively studied light nonmagnetic metals (NMs) for OT devices, theoretical calculations of the resulting torque have remained limited. Here, we present a systematic and quantitative theoretical study of current-induced torques in Ti/FM and Cu/FM (FM = Co, Ni) bilayers using realistic tight-binding models derived from ab initio electronic structures. We find that the torque in Ti/FM is larger for Ni than for Co, but this trend does not necessarily hold in Cu/FM, revealing that the FM dependence of OT is not universal but varies with the orbital current source. Moreover, the dependence of OT on NM thickness clearly indicates its NM bulk origin in both Ti- and Cu-based systems. Notwithstanding, the quantitative characteristics of OT cannot be explained by a simplified picture based on the individual bulk properties of the NM or FM layers. These results provide microscopic insight and practical guidance for designing light-metal-based orbitronic devices.

Charge-to-orbital conversion via the orbital Rashba-Edelstein effect represents a key functionality for orbitronics but has been challenging to identify. Here, we combine first-principles density functional theory, linear-response theory, and magneto-optical modeling to reveal how this effect can be detected optically through the quadratic magneto-optical Voigt effect in magnetic/nonmagnetic heavy-metal bilayers. We find that, in a cobalt/platinum bilayer, the current-induced orbital angular momentum can exceed the spin contribution by nearly a factor of three and produce a strong optical signal in addition to the equilibrium Voigt effect. Our atom-resolved study reveals that the platinum layer, despite being nominally nonmagnetic, can contribute strongly because of proximity-induced and current-induced magnetic moments. These results establish magneto-optical detection as a route to probe interfacial orbital phenomena in magnetic heterostructures.

We investigate the nonequilibrium electronic and lattice dynamics of the charge-density-wave (CDW) compound 1T-TiSe₂ using ultrafast optical spectroscopy over a wide range of temperatures and pump fluences. We reveal a close relationship between the observed ultrafast dynamical processes and two characteristic temperatures: T_CDW (∼202 K) and T* (∼165 K). Two coherent phonon modes are identified: a high-frequency A_1g mode (ω₁) and a lower-frequency A_1g-CDW amplitude mode (ω₂). While both modes soften with increasing temperature, in contrast to thermal behavior we observe a pronounced fluence-induced hardening of the CDW amplitude mode on sub-picosecond timescales. This anomalous frequency upshift provides direct evidence for a nonthermal reconstruction of the lattice potential, driven by transient screening of electron-phonon renormalization by the photoexcited carrier plasma. Concomitantly, the excited-state buildup time exhibits an abrupt increase above a well-defined critical fluence below the CDW transition temperature, signaling a qualitative change in carrier relaxation dynamics. The coincidence between phonon hardening and the fluence threshold indicates that ultrafast electronic screening reshapes the effective lattice potential underlying the CDW order, promoting a nonequilibrium metallic-like response without thermal melting. Our results establish ultrafast phonon hardening as a sensitive probe of lattice potential reconstruction and highlight the fragile balance between excitonic correlations and lattice dynamics in photoexcited 1T-TiSe₂.

Understanding the mechanism driving magnetization switching in spin-orbit-torque-assisted devices remains a subject of debate. While originally attributed to the spin Hall effect and spin Rashba-Edelstein effect, recent discoveries related to orbital moments induced by the orbital Hall effect and the orbital Rashba-Edelstein effect have added complexity to the comprehension of the switching process in nonmagnet/ferromagnet bilayers. Addressing this challenge, we present a quantitative investigation of a Pt/Co bilayer by employing atomistic spin dynamics simulations, incorporating the proximity-induced moments of Pt, as well as electrically induced spin and orbital moments obtained from first-principles calculations. Our layer-resolved model elucidates the dampinglike and fieldlike nature of the induced moments by separating them according to their even and odd magnetization dependence. In addition to demonstrating that a larger fieldlike spin-orbit-torque contribution comes from previously disregarded induced orbital moments, our work highlights the necessity of considering interactions with Pt-induced moments at the interface, as they contribute significantly to the switching dynamics.