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Terahertz waves generated with spin current flow

Using quantum magnetic current flow, so-called spin current, in magnetic metal nanostructures, physicists at Technische Universität Kaiserslautern (TUK) say they have developed a new way to generate terahertz (THz) waves.

The research field of THz spintronics technology is an emerging field. Only recently, research colleagues in Berlin showed for the first time that THz waves can be generated by spin current.

Conventionally produced via powerful radiation sources, which is associated with high energy consumption and cost, TUK believes this new method will be much more cost-effective and efficient.

Associate Professor, Dr Evangelos Papaioannou and his team at TUK have developed a special nanostructure to enable this new technique. This is said to comprise a metal bilayer of magnetic iron and non-magnetic platinum, which are layers just a few nanometers thick.

Using a femtosecond laser, the team said it could generate THz waves.

"When the laser pulses hit the nanostructure they stimulate the electrons in the iron film, creating a spin current," explains Dr Papaioannou. The current flows into the adjacent platinum layer and according to the team, causes the inverse Spin-Hall Effect.

"The atomic nuclei of platinum deflect electrons with a left- and right-handed spin in opposite directions, which leads to the transformation of the spin current into an ultrafast transient charge current, which is then the source of terahertz waves,” continues Dr Papaioannou.

The team experimented by attaching a small silicon lens to the structure to ‘bundle’ the waves. The idea behind it is that the THz waves can be forwarded easily and efficiently in future applications.

The TUK team outlined in a recent paper how the layer thickness and arrangement of materials must be best designed to generate the THz waves.

The hope is the work has revealed a way to optimise the emitters so they can reach their maximum efficiency, making them a potential for industry applications such as material testing and security techniques.

Bethan Grylls

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