Abstract-Modification of spintronic terahertz emitter performance through defect engineering

Dennis M. Nenno, Laura Scheuer, Dominik Sokoluk, Sascha Keller, Garik Torosyan, Alexander Brodyanski, Jörg Lösch, Marco Battiato, Marco Rahm, Rolf H. Binder, Hans C. Schneider, René Beigang,  Evangelos Th. Papaioannou

https://www.nature.com/articles/s41598-019-49963-8

Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for the generation of THz radiation based on spin-to-charge conversion in the layers. The key technological and scientific challenge of THz spintronic emitters is to increase their intensity and frequency bandwidth. Our work reveals the factors to engineer spintronic Terahertz generation by introducing the scattering lifetime and the interface transmission for spin polarized, non-equilibrium electrons. We clarify the influence of the electron-defect scattering lifetime on the spectral shape and the interface transmission on the THz amplitude, and how this is linked to structural defects of bilayer emitters. The results of our study define a roadmap of the properties of emitted as well as detected THz-pulse shapes and spectra that is essential for future applications of metallic spintronic THz emitters.

Abstract-Enhanced performance of spintronic terahertz emitters based on defect engineering

Sascha Keller, Dennis M. Nenno, Garik Torosyan, Laura Scheuer, Marco Battiato, Jörg Losch, Alexander Brodyanski, Rolf H. Binder, Hans C. Schneider, Rene Beigang, Evangelos Th. Papaioannou

https://arxiv.org/abs/1901.10011

Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for the generation of THz radiation based on the spin-to-charge conversion in the films. The key technological and scientific challenge of THz spintronic emitters is to increase their low intensity and frequency bandwidth. Our work reveals the factors to engineer both by introducing the scattering lifetime and the inteface transmission for spin polarized, non-equilibrium electrons. We resolve the role played by the electron-defect scattering lifetime on the spectral shape and the interface transmission on the THz amplitude and how this is linked to structural defects of bilayer emitters. The results of our study define a roadmap of the properties of the emitted as well as the detected THz-pulse shapes and spectra that is essential for future applications of metallic spintronic THz emitters.

Abstract-Efficient Terahertz Generation Using Fe/Pt Spintronic Emitters Pumped at Different Wavelengths

Evangelos Th. Papaioannou, Garik Torosyan, Sascha Keller, Laura Scheuer, Marco Battiato, Valynn Katrine Mag-usara, Johannes L'huillier, Masahiko Tani, René Beigang

https://128.84.21.199/abs/1803.08838

Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect, a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively investigated so far only at 800-nm excitation wavelength using femtosecond Ti:sapphire lasers. In this work, we demonstrate that an optimized spintronic bilayer structure of 2-nm Fe and 3-nm Pt grown on 500 {\mu}m MgO substrate is just as effective as a THz radiation source when excited either at {\lambda} = 800 nm or at {\lambda} = 1550 nm by ultrafast laser pulses from a fs fiber laser (pulse width close to 100 fs, repetition rate around 100 MHz). Even with low incident power levels, the Fe/Pt spintronic emitter exhibits efficient generation of THz radiation at both excitation wavelengths. The efficient THz emitter operation at 1550 nm facilitates the integration of such spintronic emitters in THz systems driven by relatively low cost and compact fs fiber lasers without the need for frequency conversion.

Abstract-Efficient Spintronic Terahertz Emitters Based on Epitaxial Grown Fe/Pt Layer Structures

Garik Torosyan, Sascha Keller, Laura Scheuer, Rene Beigang, Evangelos Th. Papaioannou

https://arxiv.org/abs/1707.08894

We report on efficient generation of pulsed broadband terahertz radiation utilizing the inverse spin hall effect in Fe/Pt bilayers on MgO and sapphire substrates. The emitter was optimized with respect to layer thickness, growth parameters, substrates and geometrical arrangement. The experimentally determined optimum layer thicknesses were in qualitative agreement with simulations of the spin current induced in the ferromagnetic layer. Our model takes into account spin diffusion and accumulation and electrical as well as optical properties of the bilayer samples. Using the device in a counterintuitive orientation a Si lens was attached to increase the collection efficiency of the emitter. The optimized emitter provided a bandwidth of up to 8 THz which was mainly limited by the low-temperature-grown GaAs (LT-GaAS) photoconductive antenna used as detector and the pulse length of the pump laser. The THz pulse length was as short as 220 fs for a sub 100 fs pulse length of the 800 nm pump laser. Average pump powers as low as 25 mW (at a repetition rate of 80 MHz) have been used for terahertz generation. This and the general performance make the spintronic terahertz emitter compatible with established emitters based on nonlinear generation methods.