The modulation of THz spintronic emitters represents a real challenge nowadays. Here, we consider a THz emitter made of 2D materials grown by molecular beam epitaxy (MBE) on large area and transferred on LiNbO3. The low dimensional character makes this system sensitive to the ferroelectric polarization of LiNbO3. Using this proximity effect, we demonstrate the modulation of spintronic THz emission by the ferroelectric modification of the inverse Rashba Edelstein effect in the 2D materials.
Illustration of THz spintronic emission modulation by ferroelectric polarization.
Spintronic THz emitters based on spin-to-charge conversion are promising candidates to build new compact and energy efficient THz technologies. In this prospect, the modulation of THz emission at low energy cost remains challenging today. One possible route consists in using ferroelectricity to modulate spin-orbit coupling. Thanks to their low dimensional character and large spin-orbit coupling, 2D materials such as transition metal dichalcogenides (TMD) coupled to a ferroelectric material represent good candidates. Here, we demonstrate such ferroelectric modulation of THz spintronic emission in the CoFeB/ PtSe2/MoSe2/LiNbO3 stack.
We use MBE in the van der Waals regime to grow the PtSe2/MoSe2 bilayer epitaxially on mica. This bilayer is then transferred using a wet method (in DI water) onto a bidomain LiNbO3 substrate as shown in the figure. Using several characterization techniques, we confirm that the TMD bilayer structural and electronic properties are preserved after transfer. After thermal surface treatment under ultrahigh vacuum, the PtSe2/MoSe2/LiNbO3 stack is covered with 3 nm of CoFeB and 4 nm of Al grown by sputtering. THz time-domain spectroscopy is performed by exciting the stack with 80 fs laser pulses at 800 nm with linear polarization. THz pulses are detected with a 250 µm-thick ZnTe crystal. As sketched in the figure, a clear difference in amplitude (up to 22 %) between the THz signal for the LiNbO3 polarization up (Pup) and polarization down (Pdown) can be observed demonstrating the ferroelectric modulation of THz spintronic emission. DFT calculations show that spin-to-charge conversion takes place at the interface between PtSe2 and MoSe2 through the inverse Rashba Edelstein effect. They also show that the ferroelectric modulation comes from the opposite shifts of the TMD bilayer Fermi level induced by the polarization up (Pup) and polarization down (Pdown) of LiNbO3.
Our results open perspectives for the realization of efficient THz modulators based on field effect spin–orbit devices integrating 2D materials.
Team: 2D Spintronics and Materials growth (plateforme Cluster 2D)
Collaboration: Laboratoire de Physique de l’ENS (Paris), Laboratoire Albert Fert (Palaiseau)
Funding: ESR/EQUIPEX+ ANR-21-ESRE-0025 2D-MAG projects, PEPR SPIN ANR-22-EXSP-0003 TOAST, PEPR SPIN ANR-22-EXSP-0009 SPINTHEORY
Further reading: Inverse Rashba Edelstein THz emission modulation induced by ferroelectricity in CoFeB/PtSe2/MoSe2//LiNbO3 systems, S. Massabeau, O. Paull, A. Pezo, F. Miljevic, M. Micica, A. Grisard, P. Morfin, R. Lebrun, H. Jaffrès, S. Dhillon, J.-M. George, M. Jamet, and M. Bibes, APL Materials 13, 041102 (2025). Open access: hal-05064688
Contact: Matthieu Jamet