Jaroslav Fabian: "A breakthrough in the field of spintronics"

⏹ Why is 2DSPIN-TECH important?  

➡️ – 2DSPIN-TECH brings together several expert groups, each with unique and complementary expertise, aimed at demonstrating spin-orbit torque functionalities in a laboratory environment. The consortium possesses a complete chain of capabilities necessary to achieve the final demonstration, encompassing growth and fabrication facilities, advanced characterization techniques, and methodologies for measuring charge and spin transport. Additionally, and this is where my group in Regensburg comes in, the consortium benefits from robust theoretical frameworks and simulation techniques to complement experimental efforts. Thus, 2DSPIN-TECH is wholly dedicated to its primary objective: demonstrating controllable spin-orbit torque in 2D materials. Achieving this milestone would constitute a breakthrough in the field of spintronics, says Jaroslav Fabian.

⏹ What is the benefit of using spintronics instead of charged electrons for memory technology? 

➡️ – Spintronics significantly enhances the capabilities of traditional charge-based electronics by introducing electron spin as a novel control knob. While electrons are useful for processing information, say in computer logic, they fail to retain it due to the transient nature of electronic states in solids. Electrons scatter frequently off atomic vibrations, losing the memory of their initial states. In contrast, electron spin persists for longer periods owing to its relatively weak interaction with the lattice degrees of freedom. This endurance makes electron spin, the fundamental source of magnetism, an exceptional candidate for information storage. 

– In practice, we encode information within a magnet by manipulating its magnetization, representing binary states as either magnetization up or down, along a preferred orientation. Subsequently, we can detect this magnetically stored information by observing the effect of the magnetization on electric current. However, if we wish to modify information, we need to flip the magnet. This is where spin-orbit torque enters.  By passing an electric current through a two-dimensional magnet, the spin-orbit coupling generates sufficient torque to induce magnetization reversal. At 2DSPIN-TECH, we are confident in our ability to achieve magnet flipping through spin-orbit torque. This approach promises fast and energy-efficient information writing, enabling atom-thin and highly tunable non-volatile magnetic memory elements.  

⏹ What is spin-orbit coupling? In which ways can we increase spin-orbit coupling by applying 2D materials? 

➡️ – Spin-orbit coupling is a fundamental interaction rooted in relativistic quantum physics, which posits that each electron possesses a spin degree of freedom. Classically envisioned as rotation, the electron's spin generates a magnetic moment, rendering it susceptible to manipulation by magnetic fields.  

– Spin-orbit coupling intertwines the electron's spin and velocity: electrons with opposite spins and identical velocities experience distinct trajectories under the influence of an electric field, enabling the discrimination of spin orientations solely through electrical means. This coupling holds great promise for spintronics, as it allows for the electrical manipulation of electron spins, and conversely, the magnetic control of electric currents or voltages by modifying spin orientations. 

– In the realm of 2D materials and their van der Waals heterostructures, spin-orbit interactions can be deliberately engineered and controlled. Typically, in solid-state systems, spin-orbit coupling manifests as an effective, velocity-dependent spin-orbit vector field. Electrons moving with opposite velocities exhibit opposite spin-orbit fields. By carefully selecting material combinations, various types of spin-orbit fields with diverse magnitudes and orientations can be realized. The most common is the Rashba field, which appears in any heterostructure due to the interface of materials.  

– Spin-orbit coupling underpins numerous phenomena in condensed matter physics, including the spin Hall effect, spin relaxation, topological protection, spin-charge conversion, or spin-orbit torques. The last are actively investigated within the 2DSPIN-TECH consortium, contributing to advancements in spin-based technologiess.

⏹ What is Rashba angle? How to change spin-orbit coupling by twisted angles of 2D materials? 

➡️ – As electrons move in the plane of a two-dimensional material, the Rashba coupling is manifested as an effective magnetic field pointing perpendicular, still within the 2D sheet, to the electron’s velocity. This field aligns the electron spins. In twisted heterostructures, which are created by stacking two-dimensional materials with a twist between them, the effective field can be tilted away from the perpendicular direction. This tilt is the Rashba angle. When the Rashba angle is zero, the effective magnetic field is perpendicular to the electron's velocity, whereas at 90°, it aligns with the velocity – this is termed unconventional Rashba coupling. This ability to control the Rashba effect offers opportunities for engineering spintronic devices and exploring novel quantum phenomena. 

⏹ Do you think 2D materials will be a game changer for spintronics? 

➡️ –  Absolutely. 2D materials have already revolutionized fundamental spintronics research. The key factor is tunability. Not only there are many electronic and magnetic varieties of 2D materials – metals, semiconductors, insulators, ferromagnets, antiferromagnets – they are also highly tunable by electric fields, by doping, by stacking, twisting, or straining. For instance, the application of an electric field perpendicular to a stack of 2D materials can effectively toggle the spin-orbit coupling of electrons, laying the foundation for spin transistors. There is currently a significant push to discover stable 2D magnets exhibiting magnetization well above room temperature. Achieving this goal holds the promise of making a tangible impact on magnetic memory-based electronics. 

Text and photo: Jonas Löfvendahl

4 facts about Jaroslav Fabian

✅ Professor at the University of Regensburg in Germany.

✅ Favorite quote: “Persist in solving, and the solution will come.” (Lev Landau) 

✅ Likes to do in spare time: Enjoy every moment with family.

✅ Has worked with Graphene and other 2DM since 2010.

Read more about 2DSPIN-TECH here.