Phys. Rev. Lett. 128, 157205 (2022)

Light-Induced Magnetization at the Nanoscale

Jonas Wätzel¹, Primož Rebernik Ribič², Marcello Coreno^2,3, Miltcho B. Danailov², Christian David⁴, Alexander Demidovich², Michele Di Fraia², Luca Giannessi^2,5, Klavs Hansen⁶, Špela Krušič⁷, Michele Manfredda², Michael Meyer⁸, Andrej Mihelič⁷, Najmeh Mirian^2,9, Oksana Plekan², Barbara Ressel¹⁰, Benedikt Rösner⁴, Alberto Simoncig², Simone Spampinati², Matija Stupar¹⁰, Matjaž Žitnik⁷, Marco Zangrando^2,11, Carlo Callegari², Jamal Berakdar¹ and Giovanni De Ninno^2,10,*

1 Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle (Saale), Germany

2 Elettra-Sincrotrone Trieste S.C.p.A., 34149 Trieste, Italy

3 ISM-CNR, in Basovizza Area Science Park, 34149 Trieste, Italy

4 Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland

5 INFN-LNF, Via E. Fermi 40, 00044 Frascati (Rome), Italy

6 Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, 300072 Tianjin, China

7 J. Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia

8 European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany

9 Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg, Germany

10 University of Nova Gorica, 5000 Nova Gorica, Slovenia

11 Istituto Officina dei Materiali, Consiglio Nazionale delle Ricerche, 34149 Trieste, Italy

Abstract

Triggering and switching magnetic moments is of key importance for applications ranging from spintronics to quantum information. A noninvasive ultrafast control at the nanoscale is, however, an open challenge. Here, we propose a novel laser-based scheme for generating atomic-scale charge current loops within femtoseconds. The associated orbital magnetic moments remain ferromagnetically aligned after the laser pulses have ceased and are localized within an area that is tunable via laser parameters and can be chosen to be well below the diffraction limit of the driving laser field. The scheme relies on tuning the phase, polarization, and intensities of two copropagating Gaussian and vortex laser pulses, allowing us to control the spatial extent, direction, and strength of the atomic-scale charge current loops induced in the irradiated sample upon photon absorption. In the experiment we used He atoms driven by an ultraviolet and infrared vortex-beam laser pulses to generate current-carrying Rydberg states and test for the generated magnetic moments via dichroic effects in photoemission. Ab initio quantum dynamic simulations and analysis confirm the proposed scenario and provide a quantitative estimate of the generated local moments.