IN²UB INTERNATIONAL RESEARCH SEMINARS
Spin-charge interconversion with low-symmetry materials
By, Prof. Fèlix Casanova, CIC nanoGUNE BRTA, San Sebastian, Basque Country (Spain) / IKERBASQUE, Basque Foundation for Science, Bilbao, Basque Country (Spain)
Date and Venue: November 29th, 2024 at 12.00h – Sala de Graus Eduard Fontserè (Faculties of Physics and Chemistry UB)
(Chaired by Prof. Xavier Batlle, IN²UB and Faculty of Physics UB)
Abstract:
Two-dimensional materials are an exciting new material family in which the proximity effect is especially important and opens ways to transfer useful spintronic properties from one 2D material into another. For instance, transition metal dichalcogenides (TMD) can be used to enhance the spin-orbit coupling of graphene. The spin-orbit proximity in such graphene/TMD van der Waals heterostructures leads to spin-to-charge conversion (SCC) of out-of-plane spins due to spin Hall effect (SHE), first observed by our group using MoS2 as the TMD [1]. The combination of long-distance spin transport and SHE in the same material gives rise to an unprecedented figure of merit (product of spin Hall angle and spin diffusion length) of 40 nm in graphene proximitized with WSe2, which is also gate tunable [2].
The low symmetry present in many of these low-dimensional materials allows the creation of spin polarizations in unconventional directions and enables new fundamental effects and configurations for devices. In this regard, chiral systems are the ultimate expression of broken symmetry, lacking inversion and mirror symmetry. One way to achieve this is by twisting a graphene/TMD heterostructure. We use twisted graphene/WSe2 to observe SCC arising from Rashba-Edelstein effect (REE) from spins not only perpendicular to the current (conventional configuration), but also parallel to the current (unconventional configuration) [3]. Furthermore, we can tune the twist angle between graphene and WSe2 to control the helicity of the Rashba spin texture, which even changes sign, in excellent agreement with theoretical predictions [4].
Another way to exploit chirality is by directly using materials with a chiral crystal structure, such as elemental tellurium (Te), a 1D van der Waals material. We have demonstrated a gate-tunable chirality-dependent charge-to-spin conversion in Te, [5], detected by recording a large unidirectional magnetoresistance (up to 7%). The orientation of the electrically generated spin polarization is determined by the crystal handedness, while its magnitude can be manipulated by an electrostatic gate. These results pave the way for the development of chirality-based spintronic devices.
References: [1] C. K. Safeer, FC et al., Nano Lett. 19, 1074 (2019). [2] F. Herling, FC et al., APL Mater. 8, 071103 (2020). [3] H. Yang, FC et al., Nat. Mater. (2024). [4] S. Lee, FC et al. Phys. Rev. B 106, 165420 (2022). [5] F. Calavalle, FC et al., Nat. Mater. 21, 526 (2022).
About the author:
Fèlix Casanova is an Ikerbasque Research Professor at CIC nanoGUNE (San Sebastian, Spain). He obtained his Ph.D. in Physics from the University of Barcelona in 2004 and was a postdoctoral researcher at the University of California, San Diego from 2005 to 2009. Since 2009, he has been the coleader of the Nanodevices Group at CIC nanoGUNE, which currently has more than 30 members. His current research interests are focused on spintronics in metals, magnetic insulators and 2D materials, where pure spin currents are created, transported and manipulated using different spin-dependent phenomena as a future alternative to conventional electronics. His pioneering studies on spin-charge interconversion have led to an ongoing collaboration with Intel, world-leading microelectronics company. He has been invited to the most important international conferences and given seminars at universities and research centers worldwide. He was Editorial Board member of Physical Review Applied, published by the APS, between 2016 and 2022. He has been distinguished two times (2020 and 2022) with the Outstanding Researcher Award by Intel.
With the support of the Doctoral program in Nanosciences