Light Pulses Generate Nearly 100 Per Cent Pure Spin Current in Novel Material

Deepika Gill and colleagues at the Max-Born-Institute for Non-Linear optics in collaboration with Rutherford Appleton Laboratory have achieved the all-optical generation of pure spin current in the altermagnet Cr 2 SO, challenging the previous understanding that such materials were unsuitable for this purpose. Combining infrared valley excitation with a terahertz pulse envelope creates nearly 100% pure spin currents. This process circumvents the need for charge flow and uses a valley selection rule linked to linearly polarised light, offering a practical pathway towards lightwave control of spin with minimal intrinsic spin mixing. The findings sharply broaden the scope of materials suitable for spintronics and ultrafast information processing.

Infrared and terahertz pulses manipulate electron momentum within altermagnet valley structures

Infrared valley excitation, a technique utilising light to target specific energy states within a material, was combined with a terahertz pulse envelope to achieve this result. A terahertz pulse envelope delivers a fast burst of energy, subtly altering the flow of spin, much like a quick tap on a spinning top. Altermagnets possess unique ‘valley manifolds’, the specific energy landscape dictating electron behaviour, which previously hindered the generation of pure spin current; this pairing proved key to overcoming this obstacle.

Electrons in these valleys were selectively excited by carefully tuning the infrared light, while the accompanying terahertz pulse shifted their momentum, preventing cancellation of the spin current. This combination overcomes limitations posed by the anisotropic valley manifolds present in altermagnets, which typically prevent the compensation needed for pure spin current. The approach selectively excites electrons with infrared light, then uses the terahertz pulse to shift their momentum and prevent current cancellation, resulting in nearly 100% spin current purity.

Terahertz pulse control enables near-perfect spin current generation in chromium disulfoxide

Nearly 100% pure spin currents have been generated in the altermagnet Cr₂SO, a material once deemed unsuitable for ultrafast spin current generation due to its valley configuration. This breakthrough surpasses the limitations of two-dimensional altermagnets, which traditionally suffer from internal structural constraints preventing efficient compensation of valley charge; this compensation is essential for generating pure spin current without accompanying charge flow. A terahertz pulse envelope manipulates electron momentum, effectively circumventing the need for spin-orbit coupling and minimising intrinsic spin mixing, while infrared light selectively excites electrons in specific energy states.

Chromium disulfoxide (Cr₂SO) has now yielded nearly 100% pure spin currents, despite previously being considered unsuitable for this purpose due to its unique valley configuration. This was achieved through a combination of infrared light and a terahertz pulse envelope manipulating electron momentum, bypassing the need for spin-orbit coupling, a common cause of signal degradation in other materials. Linearly polarized light creates charge exclusively at specific valleys within the material, avoiding unwanted excitation elsewhere in the Brillouin zone, a region of reciprocal space defining electron behaviour. Temporal analysis of charge revealed vanishing charge current following the pulse, indicating highly efficient spin current generation, validated using a tight-binding approach based on ab-initio band structure calculations.

Terahertz radiation unlocks spin currents in previously unsuitable magnetic materials

Generating spin without charge offers tantalising possibilities for low-energy data storage and processing. This work demonstrates a route to achieving this in chromium disulfoxide, a material previously dismissed due to its internal structure hindering efficient spin current generation. Scientists acknowledges that this technique remains demonstrated only within a single material, and generalising this approach to other altermagnets presents a significant challenge.

Despite the hurdle of replicating this success across diverse materials, the demonstration of pure spin current generation in chromium disulfoxide is nonetheless significant. Terahertz radiation, electromagnetic radiation between microwaves and infrared light, has been harnessed to achieve this. Scientists has demonstrated a new technique for generating pure spin current using light in chromium disulfoxide, overcoming limitations previously thought insurmountable.

Control of spin without charge flow is now possible through the combination of infrared and terahertz radiation, potentially enabling faster and more efficient data storage. This work establishes a new method for manipulating spin, demonstrating the all-optical generation of nearly 100% pure spin current within the altermagnet Cr₂SO, a material where spin flows without accompanying charge. The anisotropic valley manifolds, the unique energy landscape governing electron behaviour, within two-dimensional altermagnets previously presented limitations; this achievement circumvents them. By combining infrared light, which selectively excites electrons, with a terahertz pulse envelope that shifts their momentum, Scientists overcame the need for materials with low spin-orbit coupling, traditionally favoured for this purpose.

The researchers successfully generated nearly 100% pure spin current in the altermagnet Cr₂SO using a combination of infrared and terahertz radiation. This is significant because it demonstrates a method for controlling spin without charge flow, potentially offering advantages for data storage and processing. The technique overcomes previous limitations associated with the material’s internal structure, previously thought to preclude efficient spin current generation. The authors note that extending this approach to other altermagnets remains a key challenge for future work.