On-line SPICE-SPIN+X Seminars

On-line Seminar: 05.02.2025 - 15:00 CET

Spintronics with van der Waals heterostructures

Sergio Valenzuela, ICREA and ICN2

Van der Waals (vdW) heterostructures provide a versatile platform for investigating spintronic phenomena, particularly through their atomically sharp interfaces and tunable properties [1,2]. Such heterostructures allow for the design of proximity effects via short-range interactions, enabling the exploration of spin-orbit coupling and spin-dependent transport in ways not easily achieved with conventional materials [1].
In this talk, I will begin by addressing the importance of boundary states and the quality of the topological insulator (TI)/ferromagnet (FM) interface in maximising spin-orbit torques (SOT). For example, vdW TIs such as (Bi,Sb)2Te3 can influence spin transport and charge-to-spin conversion processes due to spin-momentum locking. I will show how introducing a non-magnetic metallic [3] or, in particular, graphene [4] interlayer between the TI and FM, when the FM is a transition metal, significantly modifies the nature and enhances the efficiency of SOTs [3,4]. Similar enhancements observed with sharp interfaces between TIs and vdW FMs [5] further illustrate the potential of interfacial engineering in shaping spintronic functionalities.
Building on these examples, I will then discuss how proximity effects in graphene can be identified through spin transport dynamics, focusing on our findings on spin relaxation anisotropy [6] and charge-to-spin interconversion [7,8]. I will highlight the role of crystal symmetry, showing how systems with reduced symmetry give rise to diverse spin-orbit fields and unconventional charge-to-spin conversion components, alongside methods for determining their underlying mechanisms. Furthermore, I will demonstrate that electrostatic gating can tune spin relaxation anisotropy, as well as spin Hall and spin galvanic effects, with these phenomena remaining robust up to room temperature [6-8].

[1] J. F. Sierra et al., Nature Nano. 16, 856–868 (2021)
[2] H. Yang, S. O. Valenzuela et al., Nature 606, 663 (2022)
[3] F. Bonell et al., Nano Lett. 20, 5893 (2020)
[4] R. Galceran et al., Adv. Mater. Interfaces 9, 2201997 (2022): T. Guillet, V. Zatko et al., unpublished (2025)
[5] T. Guillet et al., Nano Lett. 24, 822 (2024)
[6] B. Raes et al. Nature Commun. 7, 11444 (2016); L. A. Benítez et al., Nature Phys. 14 (2018); APL Materials 7, 120701 (2019); J. F. Sierra, J. Světlík et al., Nature Mater. (in press 02/2025)
[7] L. A. Benítez et al., Nature Mater. 19, 170 (2020)
[8] L. Camosi et al., 2D Mater. 9, 035014 (2022)

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.

On-line SPICE-SPIN+X Seminars

On-line Seminar: 11.02.2026 - 15:00 CET

TBA

Yossi Paltiel, HUJI

TBA

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.

On-line SPICE-SPIN+X Seminars

On-line Seminar: 05.03.2025 - 15:00 CET

On the Origin of Electron-Electron Interactions in Bi2Se3 Topological Thin Films

Bryan J Hickey, University of Leeds

We are using Bi2Se3 as a platform in a number of applications in two large collaborative projects: NAME (Nanoscale Advanced Materials Engineering, https://name-pg.uk) and CAMIE ( Combining Advanced Materials with Interface Engineering https://camie.leeds.ac.uk). In our four-chamber deposition system we grow Bi2Se3 by MBE and transfer the samples under UHV to other chambers where we deposit additional layers such as ferromagnets, antiferromagnets, skyrmion bearing multilayers as well as organic layers such as C60. The groundwork for these projects required a growth campaign to obtain material of world class standard and we have characterised our Bi2Se3 using a wide range of techniques. We have achieved excellent epitaxy using a seed layer of (Bi,In)2Se3 and most of the results there are on layers of 20nm Bi2Se3.
Research into the transport properties of Bi2Se3 has been ongoing for many years but there are still questions to be answered about the nature of the conduction in this interesting material. For example, the spin-orbit lifetime is often assumed to be very short but results can be difficult to interpret when the number of conduction channels is reported to be other than 1 or 2, and frequently, it is less than 1. Equally, the spin-orbit scattering should be independent of temperature but it often cannot be seen to be so in many results. Although several papers have suggested that electron-electron interaction effects are observed in, especially the zero-field low-temperature upturn in the resistivity, the nature and origin of these interactions remains unreported.
We have extracted the lifetime of the spin-orbit interaction (!"), by fitting the full expression of the Hikami, Larkin and Nagaoka (HLN) theory for the MR, which is indeed short in the best materials ~ 10-14 s but can be longer in others. We show that fits to the MR can be achieved with a temperature independent value of !". In the strong spin-orbit limit, the approximate HLN function applies and then the fits return only a single conduction channel. The full analysis allows us to extract the electron-electron interaction time (## )
as a function of temperature and hence determine its origin in terms of Fermi liquid theory
and the effects of a finite mean free path, i.e. ($ ℓ).

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.

On-line SPICE-SPIN+X Seminars

On-line Seminar: 08.01.2025 - 15:00 CET

Probing 2D Magnetic Materials with magnetotransport

Alberto Morpurgo, University of Geneva

The ability to exfoliate van der Waals crystals of magnetic compounds is giving access to a vast, unexplored family of two-dimensional magnetic materials, with a variety of different magnetic ground states. Most of these compounds are semiconductors that offer –besides the possibility to explore magnetism in highly controlled 2D crystals— a new playground to combine magnetic and semiconducting functionalities. In this talk I will discuss how magnetotransport experiments allow the investigation the magnetic phase diagram of 2D magnetic material down to the ultimate limit of individual monolayers, to reveal phenomena that are difficult –or cannot—be accessed with other existing experimental techniques. After a short introduction, in my talk I will discuss vey recent experiments on field effect transistors realized on exfoliated crystals of CrPS4 –ranging from relatively thick multilayers, to double-gated bilayers, and to individual monolayers– and discuss results that illustrate the wealth of physical phenomena that become accessible with these systems.

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.
PDF file of the talk available here

On-line SPICE-SPIN+X Seminars

On-line Seminar: 30.10.2024 - 15:00 CET

Quantum Functionalities of Magnetic Skyrmions

Christina Psaroudaki, ENS Paris

In this talk, I will discuss the development of magnetic nano-skyrmions as promising candidates for quantum logic elements, focusing on their potential applications in quantum computing. Nano-skyrmions possess quantized helicity excitations, and quantum tunneling between skyrmions with distinct helicities highlights their quantum nature. By harnessing these unique properties, we propose skyrmion qubits where information is stored in the quantum degree of helicity. Electric and magnetic fields can adjust the logical states of these qubits, offering a versatile operation regime with high anharmonicity.

I will explore the role of electrical control over helicity, opening new pathways for functionalizing collective spin states. Additionally, I will discuss the microwave pulses necessary to generate single-qubit gates and multiqubit schemes that promise scalable architectures with tailored couplings. Scalability, controllability by microwave fields, and nonvolatile readout techniques converge to make skyrmion qubits highly attractive for quantum processors. This talk will highlight the exciting developments, challenges, and potential breakthroughs in quantum magnetism and quantum information using skyrmions.

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.
PDF file of the talk available here

On-line SPICE-SPIN+X Seminars

On-line Seminar: 27.11.2024 - 15:00 CET

Fractional Charges in 2D magnets & Aharonov-Bohm scattering

Nina del Ser, Caltech

Magnetic skyrmions are characterised by an integer topological charge, Q=1, while merons have half-integer winding numbers, Q=1/2. In this talk, I will describe the physics of magnetic textures with fractional topological charge, which is neither integer nor half-integer. Examples of generic magnetic systems which can host such fractional charges include the meeting points between domains in ferromagnetic films with cubic anisotropy or exploding skyrmions. Only fractionally charged defects give rise to an Aharonov-Bohm effect for incident magnons. We investigate this in a numerical scattering experiment by tracking the magnon-induced forces.

Please sign up here in order to get the Zoom link and regular announcements of the upcoming talks.
PDF file of the talk available here