Spin-sonics: Acoustic wave gets the electrons spinning

Date:
July 29, 2021
Source:
University of Mu"nster
Summary:
Researchers have succeeded in detecting the rolling movement of
a nano- acoustic wave predicted by the famous physicist and Nobel
prize-winner Lord Rayleigh in 1885.



FULL STORY ==========================================================================
A team of German and American researchers from Augsburg, Mu"nster,
Edmonton, West Lafayette and Munich have detected the rolling movement
of a nano-acoustic wave predicted by the famous physicist and Nobel prize-winner Lord Rayleigh in 1885. In a study published in the journal "Science Advances", the researchers use a nanowire inside which electrons
are forced onto circular paths by the spin of the acoustic wave. This phenomenon can find applications in acoustic quantum technologies or in so-called phononic components which are used to control the propagation
of acoustic waves.


========================================================================== Acoustic waves are incredibly versatile in modern nanophysics, as they
can influence both electronic and photonic systems. For example, minute
micro- acoustic chips in computers, smartphones or tablets ensure that
the wireless signals received are electronically processed. However,
despite the wide- ranging uses to which nano-acoustic waves can be put,
the fundamental property of spin of the nano-acoustic wave was never
detected till date.

"Since Lord Rayleigh's pioneering work it has been known that there are acoustic waves which propagate on the surface of solids and which show a
highly characteristic elliptical rolling movement," explains Dr. Hubert Krenner, a Professor Physics, who headed the study at the University of Augsburg and recently moved to the University of Mu"nster. "In the case
of nano-acoustic waves we have now succeeded in observing directly this transversal spin, which is what we physicists call this movement."
In their study, the researchers used an extremely fine nanowire
which was positioned on a so-called piezoelectric material -- Lithium
Niobate. This material becomes deformed when subjected to an electrical current, and, with the aid of small metal electrodes, an acoustic wave
can be generated on the material. On the surface of the material, the
acoustic wave generates an elliptically rotating (gyrating) electrical
field. This, in turn, forces the electrons in the nanowire onto circular
paths. Prof. Zubin Jacob, from Purdue University, is excited about
the result. "So far we knew about this phenomenon for light," he says,
"Now we have succeeded in demonstrating that this is a universal effect
which also occurs in other types of waves such as sound waves on a technologically important platform -- Lithium Niobate." The research
results presented are a milestone, as the transversal spin now observed
for the first time can be used specifically to control nano-systems
or transfer information. As Maximilian Sonner, a PhD student at the
Institute of Physics at Augsburg, explains, "We observe the movement of electrons in the nanowires, which were made at the Technical University
of Munich, through the light emitted by the electrons." His colleague
Dr. Lisa Janker adds, "We use an extremely rapid stroboscope here which
enables us to practically observe this movement in real time -- even
at higher frequencies up to the gigahertz range." Dr. Farhad Khosravi,
who recently completed his PhD in Zubin Jacob's research group, says, "I
was able to transfer my calculations for light directly to the Rayleigh acoustic wave. It has been known for a long time that light waves and
sound waves have similar properties. Nevertheless, the extent of the
match for their spin properties is really phenomenal." The researchers
are convinced that the universal principle of spin-physics underlying
this phenomenon will lead to important technological advances. "The
study which has now been published in Science Advances is just a first
step - - but a decisive one," says Hubert Krenner. The researchers
are now working hard to link the transversal spin of acoustic waves
with the spin of other waves. "What we need to do next," says Zubin
Jacob, "is use this transversal acoustic spin specifically in order to manipulate optical quantum systems or the spin of light, for example." ========================================================================== Story Source: Materials provided by University_of_Mu"nster. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Maximilian M. Sonner, Farhad Khosravi, Lisa Janker, Daniel Rudolph,
Gregor Koblmu"ller, Zubin Jacob, Hubert J. Krenner. Ultrafast
electron cycloids driven by the transverse spin of a surface
acoustic wave.

Science Advances, 2021; 7 (31): eabf7414 DOI: 10.1126/sciadv.abf7414 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210729095209.htm

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