The booming fields of antiferromagnetic spintronics and terahertz (THz) magnonics urge to understand the ultrafast dynamics triggered in antiferromagnets by ultrashort stimuli. The interest in ultrafast magnetism of antiferromagnets has led to new and vastly counter-intuitive findings in experimental and theoretical research. We report on the ultrafast spin and lattice dynamics in a rutile antiferromagnet.
Electric fields operating at THz frequencies hold significant promise for inducing ultrafast coherent excitations in magnetic heterostructures. Through the utilization of ferromagnetic/heavy metal (FM/HM) heterostructures, we have demonstrated that THz radiation (0.1 – 30 THz) exhibits combined functionality of microwaves and visible light. 1) Similar to microwaves, THz fields can effectively generate spin currents through the spin-Hall effect (SHE), resulting in an excitation of THz-frequency magnon modes. 2) Akin to visible light excitation, THz fields deposit heat, leading to the demagnetization of FM layers. Harnessing the THz-induced demagnetization as a spin current source within FM/HM heterostructures, we exploit the half-cycle THz electric field to incite spin currents, which subsequently transformed into picosecond charge currents through the inverse SHE within the HM layer. This conversion process results in the emission of a THz second harmonic signal, offering the THz spintronic frequency conversion.
This talk advertises scattering-type scanning near-field infrared micro-spectroscopy (s-SNIM) in the spectral range of 75 to 1.3 THz [1], as provided by the free-electron laser FELBE, the narrow-band laser-light source at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany. We demonstrate the -independent s-SNIM resolution of a few 10 nm by exploring structured Au samples, Graphene-transistors, meta-materials [2], and local ferroelectric phase-transitions down to LHe [3]. s-SNIM secondly was integrated into a THz pump-probe experiment for the inspection of excited states in structured SiGe samples. We developed a novel demodulation technique with high temporal resolution [4] hence achieving an excellent Signal-to-Noise Ratio. Thirdly using the super-radiant TELBE light source [5], HZDR recently extended the wavelength range down to 100 GHz radiation. We adapted our s-SNIM to this TELBE photon-source as well, achieving an equally high spatial resolution as with FELBE. Moreover, the superb 30-fs temporal resolution of TELBE will allow us to study a multitude of physical phenomena with sub-cycle resolution [5,6], such as spin-structures, magnons and phonon polaritons.
[1] F. Kuschewski et al., Appl. Phys. Lett. 108 (2016) 113102.
[2] S.C. Kehr et al., ACS Photonics 3 (2016) 20.
[3] J. Döring et al., Appl. Phys. Lett. 105 (2014) 053109.
[4] F. Kuschewski et al., Sci. Rep. 5 (2015) 12582.
[5] B. Green et al., Sci. Rep. 6 (2016) 22256.
[6] S. Kovalev et al., Struct. Dyn. 4 (2017) 024301.
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