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doctoral student H/F Novel rapid continuous-wave THz sources exploiting broadband inverse spin Hall effect emitters

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General information

Reference : UMR8520-FRELEF-048
Workplace : VILLENEUVE D ASCQ
Date of publication : Thursday, February 13, 2020
Scientific Responsible name : Nicolas TIERCELIN
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 4 May 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Within the FET OPEN s-NEBULA (a French-German-Swedish-Czech partnership led by THALES SA), a revolutionary approach to the generation of THz radiation is being explored exploiting ultrarapid spin-orbit interaction (SO) at the interface between magnetic/non-magnetic metallic thin films. In the inverse spin Hall effect (ISHE) a net charge current is created when a spin-polarized current is injected into a heavy 5d metal that exhibits strong SO coupling. Using short (~10fs) femtosecond laser pulses (of nJ pulse energy) shone on a Co/Pt metallic multilayer to create rapid spin current pulses, a German research consortium (and now also part of the s-NEBULA project) has demonstrated just a couple of years ago that the resulting ISHE-mediated ultrafast net charge pulse occurring in the Pt layer (~100fs) will emit in the THz frequency range. The advantage of this new type of spintronic emitter is multifold. Besides being compact and operated at room-temperature (RT), its principle, exploiting the ultrafast electron relaxation times in metals and not being hindered by phonon absorption, allows it to be ultrabroadband and potentially polarization tunable by controlling magnetization in the ferromagnetic layer. Presently, there isn't a single solid-state THz emitter that is capable of delivering such a performance. Such a source may therefore have a tremendous impact by allowing for instance ultrabroadband THz spectroscopy but also serving as emitter for secure THz communications at carrier frequencies that are not straightforwardly accessible (beyond 5THz).
Still, the field of THz spintronics is in its infancy and a lot remains to be explored. To name just a few research directions: optimization of the metallic material combinations, exploration of other spin-to-charge conversion mechanisms, (magnetic) modulation of the THz signal, and most importantly the generation of RT continuous-wave (CW) emission of THz radiation by photomixing two intense laser lines on a FM/NM multilayer. Precisely this latter challenge remains a very fertile research ground, as up till now all demonstrated THz spintronic emitters are operated in pulsed mode.

Work Context

The PhD candidate to be hired on the s-NEBULA FET contract will be in charge of demonstrating the possibility of creating continuous-wave THz emission using spintronic effects. Such a demonstration would be a world first. In a second step it will be explored how the polarization of the CW signal can be rapidly modulated by reorienting the magnetization direction in the ferromagnetic layers. For this it will be investigated whether rapid magnetoelastic effects (coupling magnetization to strain or acoustic waves) allow fast magnetization reversal. Other approaches exploit fast magnetization reversals in systems with induced strong magnetic anisotropies.

Within the framework the PhD candidate will be involved in and leading some of the steps of the research tasks : from numerical modeling of the optical excitation of the spin currents, over the microfabrication of the metallic multilayers, to magnetic, optical, and ultrafast optoelectronic spintronic devices characterization. The candidate will play an active role in developing the new experimental bench for this project. He/She will also be fully involved with the ins and outs of the EU project and as such be a part of a top-tier research consortium and getting hands-on experience with challenges of meeting research milestones and deliverables, participating in consortium progress meetups and commission review meetings.

The ideal candidate has a background in Solid-State Physics or Optoelectronics with a keen interest for characterization of ultrafast phenomena. A background in and magnetism is a definite plus. The involved IEMN research groups (THz photonics and AIMAN-FILMS) have a longstanding research track record in the field of THz photonics in general (ranging from fundamental studies to full system applications) and dynamic control of magnetic phenomena. Both research groups have an equipment portfolio allowing to immediately tackle all research challenges of the s-NEBULA project (fs lasers, photomixing setups, magnetometers, sputtering tools for the deposition of magnetic structures with emphasis on magnetoelastic materials, THz detectors and spectroscopy, ...). IEMN itself boasts the presence of one the biggest academic clean rooms (1500m2) in France offering all necessary technological fabrication infrastructures for micro- and nano-optoelectronics and micro- and nano-electromechanical systems.

Constraints and risks

Activity in clean room

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