Abstract-N\'{e}el spin orbit torque driven antiferromagnetic resonance in Mn 2 Au probed by time-domain THz spectroscopy

N. Bhattacharjee, A. A. Sapozhnik, S. Yu. Bodnar, V. Yu. Grigorev, S. Y. Agustsson, J. Cao, D. Dominko, M. Obergfell, O. Gomonay, J. Sinova, M. Kläui, H. -J. Elmers, M. Jourdan, and J. Demsar

https://journals.aps.org/prl/accepted/32071Y5cC871765f240317f6796a5ec9679dbb0ac

We observe the excitation of collective modes in the THz range driven by the recently discovered N\'{e}el spin-orbit torques (NSOT) in the metallic antiferromagnet Mn${}_2$Au. Temperature dependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 K to 450 K softens and looses intensity. Comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR). The AFMR absorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by three orders of magnitude. Based on this and the agreement with our theory modelling, we infer that the driving mechanism for the observed mode is the current induced NSOT. Here the electric field component of the THz pulse drives an AC current in the metal, which subsequently drives the AFMR. This electric manipulation of the N\'{e}el order parameter at high frequencies makes Mn${}_2$Au a prime candidate for AFM ultrafast memory applications.

Abstract-Transient increase of the energy gap of superconducting NbN thin-films excited by resonant narrow-band terahertz pulses

M. Beck, I. Rousseau, M. Klammer, P. Leiderer, M. Mittendorff, S. Winnerl, M. Helm, G. N. Gol’tsman, and J. Demsar

http://prl.aps.org/accepted/75075Y06Jb413d3903430035b96813be3c98ad3c4

Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency $2\Delta/h$. Utilizing intense, narrowband picosecond THz pulses, tuned to just below and above $2\Delta/h$ of a BCS superconductor NbN, we demonstrate that superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced non-thermal electron distribution persisting on a 100 ps timescale.