AsianScientist (Jan. 22, 2019) – Researchers in Singapore have successfully injected large spin currents into a semiconductor material, exceeding the previous record by several orders of magnitude and paving the way for practical spintronic devices. These results have been published in Nature Physics.
Electronics have helped to usher in the information age but are increasingly facing limitations imposed by the laws of physics. Spintronics, which use the spin of electrons rather than their flow to carry information, has emerged as one of the leading alternatives to conventional electronics, promising faster information processing while using less energy.
However, despite decades of research, the field has been hindered by the inability to inject spins into semiconductor materials cheaply and efficiently, a crucial first step to making useful spintronic devices. In the present study, a team of researchers led by Associate Professor Elbert Chia of Nanyang Technological University, Singapore (NTU), has now demonstrated that highly efficient spin injection can be achieved even across a bare metal to semiconductor interface.
Other senior authors from NTU include Assistant Professors Marco Battiato and Justin Song, as well as Associate Professor Yang Hyunsoo from the National University of Singapore. This work also includes collaborators from Singapore’s Agency for Science, Technology and Research and Los Alamos National Laboratory in the US.
The researchers first fabricated a single two-dimensional layer of the semiconductor material molybdenum disulfide (MoS2) coated with a magnetic layer of cobalt. They then used femtosecond laser pulses to generate spins in the cobalt layer, measuring the resulting spin currents generated in the semiconductor MoS2 layer on the other side.
As it was difficult to directly measure the ultrafast spin currents with existing technologies, the researchers made use of the high spin-orbit coupling of MoS2, which ensured that most of the spin currents generated would be converted to terahertz waves that could easily be detected. Using this proxy measure, they estimated that their method resulted in a spin current density in the MoS2 layer of 106-108 A/cm2, exceeding the previous record by 10,000 times.
“In real devices, such strong spin currents will not be required, so one can get away with considerably weaker excitations,” Chia told Asian Scientist Magazine. “Laser power a thousand times less than what we used in our experiments would be able to achieve the same kind of spin injection that we see in the spintronics industry today.”
The ability to inject spin currents into semiconductor materials in a highly efficient manner makes spintronic technology compatible with the mature semiconductor industry, thereby greatly expanding its range of applications, added Song.
“Possibly the most striking aspect is that all this was demonstrated using a simple metal-semiconductor interface, without the complicated and costly structural engineering one sees in other spintronic experiments,” said Song.
The article can be found at: Cheng et al. (2019) Far Out-of-equilibrium Spin Populations Trigger Giant Spin Injection into Atomically Thin MoS2.
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Copyright: Asian Scientist Magazine; Photo: Nanyang Technological University, Singapore.
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