New road towards spin-polarised currents

Hafniumdiselenide is a quasi twodimensional material with interesting properties for spintronics. Here, its crystal structure is shown.

Hafniumdiselenide is a quasi twodimensional material with interesting properties for spintronics. Here, its crystal structure is shown. © O. Clark/HZB

The transition metal dichalcogenide (TMD) series are a family of promising candidate materials for spintronics. A study at lightsource BESSY II has unveiled that in one of those materials even simple linear polarised light is sufficient to selectively manipulate spins of different orientations. This result provides an entirely new route for the generation of spin-polarised currents and is a milestone for the development of spintronic and opto-spintronic devices.

The second half of the 20th century was the age of electronics, electronic devices became miniaturised and even more complex, creating problems by their energy consumption and waste heat. Spintronics promises to store or transport information based on spins alone, which would work faster with much less energy. Unfortunately it is still a challenge to control spin in a material by external fields reliably and at scale.

Quasi 2D-materials in the focus

The transition metal dichalcogenide (TMD) series are the most intensely studied quasi two-dimensional materials beyond graphene, with charge density waves, superconductivity and non-trivial topological all commonplace across the material family. Hafnium diselenide (HfSe2) belongs to this class of materials. Now scientists at BESSY II have unveiled a new property of its electronic structure that could lead to a more convenient route to generate and control spin currents.

“In order to shift from electronics to spintronics, we have to find materials wherein spin up and spin down electrons behave differently”, first author Oliver Clark explains. There are two ways to do this, he points out: “We can either externally perturb the material so that electrons of different spins become functionally inequivalent, or we can use magnets where the electrons of opposite spins are functionally different intrinsically.” For the first method, the difficulty lies in finding suitable pairings of materials and mechanisms by which spin control can be externally imposed. For example, in the so-called 2H structured TMDs, one needs perfect single crystals and a circularly polarised light source. By contrast, the second method is much easier, but integrating magnets into devices is problematic for the operation of conventional electronic components, especially on small scales.

Linearly polarised light does do the trick

But between those two ways, a middle ground exists, at least for some select materials such as HfSe2:“If you probe this material with linearly-polarised light – which is easier to produce than circularly polarised light - the material acts as a magnet in terms of its spin-structure. So the spin-selectivity becomes very easy, but you do not have the problems associated with other magnetic properties”, Clark explains. The advantage: Crystal quality or orientation of the sample no longer matter.

This provides an entirely new route towards the generation of spin-polarised currents from transition metal dichalcogenides. The physicists are very excited about the implications of this work: “Our results are of relevance not only to physicists concerned with layered two-dimensional materials, but as well to specialists in spintronic and opto-spintronic device fabrication”, Clark hopes.

arö


You might also be interested in

  • Fertilisation under the X-ray beam
    Science Highlight
    19.03.2024
    Fertilisation under the X-ray beam
    After the egg has been fertilized by a sperm, the surrounding egg coat tightens, mechanically preventing the entry of additional sperm and the ensuing death of the embryo. A team from the Karolinska Institutet has now gained this new insight through measurements at the X-ray light sources BESSY II, DLS and ESRF. 
  • Neutron experiment at BER II reveals new spin phase in quantum materials
    Science Highlight
    18.03.2024
    Neutron experiment at BER II reveals new spin phase in quantum materials
    New states of order can arise in quantum magnetic materials under magnetic fields. An international team has now gained new insights into these special states of matter through experiments at the Berlin neutron source BER II and its High-Field Magnet. BER II served science until the end of 2019 and has since been shut down. Results from data at BER II are still being published.

  • Where quantum computers can score
    Science Highlight
    15.03.2024
    Where quantum computers can score
    The travelling salesman problem is considered a prime example of a combinatorial optimisation problem. Now a Berlin team led by theoretical physicist Prof. Dr. Jens Eisert of Freie Universität Berlin and HZB has shown that a certain class of such problems can actually be solved better and much faster with quantum computers than with conventional methods.