arXiv subjects

R. Rouzegar

Publications and source records attributed to R. Rouzegar.

4 recordsLinked to original sources

arXiv2026

Spatiotemporal Terahertz Emission Nanoscopy of Spintronic Photocurrents

Capturing ultrafast spin and charge photocurrents on nanoscopic scales is essential for fundamental research in physics and engineering, as well as for future applications, such as novel spinorbitronic devices. Accessing the fundamental dynamics driven by changes in electronic energy, linear momentum, and angular momentum requires probing at its native spatiotemporal scales: femtoseconds and nanometers. However, experimental approaches achieving this simultaneous resolution remain scarce and instrumentally demanding. Near-field probing offers promising platforms to combine ultrafast and nanometer resolution typically with high sensitivity to out-of-plane electric fields. However, applying this technique to in-plane ultrafast coupled spin and charge currents is largely unexplored, although being highly application-relevant - from ultrafast spin transport in 2D materials to spin-to-charge conversion in spintronic terahertz emitters (STEs). Here, we fill this gap by performing spatiotemporal terahertz (THz) emission nanoscopy (TEN) of a photoexcited fiber-coupled STE using a scanning-probe microscope. We uncover a counterintuitive, dipolar spatial evolution of the near-field THz signal, which we show originates from the out-of-plane electric fields emerging from the in-plane spin-driven charge currents. Our findings explain why TEN is sensitive to ultrafast spin-driven in-plane charge currents, paving the way for TEN to become a fully vectorial probe for the spatiotemporal mapping of coupled nanoscale THz charge and spin dynamics.

physics.optics↗

arXiv2026

Controlling Terahertz Spintronic Photocurrents in 2D-Semiconductor|Ferromagnet Heterostructures through a Functional Hybrid Interface

A profound understanding of terahertz (THz) spin and charge currents in heterostructures involving ferromagnets (FMs) and two-dimensional (2D) materials promises emerging applications in high-speed sensing and data processing. Yet, ultrafast experimental insights remain very limited. Here, we study the efficient photo-generation of THz spin and charge currents in bilayers made from the transition-metal dichalcogenide (TMD) MoS2 and the FM Co. We find that the efficiency of current generation strongly depends on the pump photon energy, as previously reported. Surprisingly, however, we observe that the current dynamics remain identical for pump photon energies above and below the MoS2 band gap. Supported by ab-initio calculations, we conclude that an interfacial hybrid metallic layer forms at the MoS2/Co boundary that has a pronounced photon-energy-dependent absorptance. Thus, the hybrid interfacial layer effectively acts like a pump-energy transducer that increases the spin-current generated in the nearby Co. Our results uncover the vital role of interfacial hybridization as a yet unexplored mechanism for efficient generation of ultrafast photocurrents in 2D-TMD|FM structures.

cond-mat.mes-hall↗

arXiv2023

Terahertz spin conductance probes of coherent and incoherent spin tunneling through MgO tunnel junctions

We study femtosecond spin currents through MgO tunneling barriers in CoFeB(2 nm)|MgO($d$)|Pt(2 nm) stacks by terahertz emission spectroscopy. To obtain transport information independent of extrinsic experimental factors, we determine the complex-valued spin conductance $\tilde{G}_d (ω)$ of the MgO layer (thickness d= 0-6 Å over a wide frequency range $(ω/2π=$ 0.5-8 THz). In the time $(t)$ domain,$ G_d (t)$ has an instantaneous and delayed component that point to (i) spin transport through Pt pinholes in MgO, (ii) coherent spin tunneling and (iii) incoherent resonant spin tunneling mediated by defect states in MgO. A remarkable signature of (iii) is its relaxation time that grows monotonically with $d$ to as much as 270 fs at $d= 6$ Å, in full agreement with an analytical model. Our results indicate that terahertz spin conductance spectroscopy will yield new and relevant insights into ultrafast spin transport for a wide range of materials.

physics.app-ph↗

arXiv2021

Laser-induced terahertz spin transport in magnetic nanostructures arises from the same force as ultrafast demagnetization

Laser-induced terahertz spin transport (TST) and ultrafast demagnetization (UDM) are central but so far disconnected phenomena in femtomagnetism and terahertz spintronics. Here, we use broadband terahertz emission spectroscopy to reliably measure both processes in one setup. We find that the rate of UDM of a single ferromagnetic metal film F has the same time evolution as the flux of TST from F into an adjacent normal-metal layer N. This remarkable agreement shows that UDM and TST are driven by the same force, which is fully determined by the state of the ferromagnet. An analytical model consistently and quantitatively explains our observations. It reveals that both UDM in F and TST in the F|N stack arise from a generalized spin voltage, which is defined for arbitrary, nonthermal electron distributions. We also conclude that contributions due to a possible temperature difference between F and N are minor and that the spin-current amplitude can, in principle, be increased by one order of magnitude. In general, our findings allow one to apply the vast knowledge of UDM to TST, thereby opening up new pathways toward large-amplitude terahertz spin currents and, thus, energy-efficient ultrafast spintronic devices.

cond-mat.mes-hall↗