In a finding that will help to identify exotic quantum states, RIKEN
physicists have seen strongly competing factors that affect an electron's
behavior in a high-quality quantum material.
Electrons have a property called spin, which can be crudely thought of as
the rotation of an electron about an axis. As an electron moves, its motion
and spin can become linked through an effect known as spin–orbit coupling.
This effect is useful because it offers a way to externally control the
motion of an electron depending on its spin—a vital ability for an emerging
technology called spintronics, which is seeking to use electron spin to
realize low-power-consumption information processing.
Spin–orbit coupling is a complex mix of quantum physics and relativity, but
it becomes a little easier to understand by envisioning a round soccer ball.
"If a soccer player kicks the ball, it flies on a straight trajectory,"
explains Denis Maryenko of the RIKEN Center for Emergent Matter Science.
"But if the player gives the ball some rotation, or spin, its path bends."
The ball's trajectory and its spinning motion are connected. If its spinning
direction is reversed, the ball's path will bend in the opposite direction.
Unlike soccer balls, electrons also interact with each other: two negatively
charged particles will repel each other, for example. This mutual repulsion
and the spin–orbit interaction compete with each other: the former can act
to align an electron's spin with that of other electrons, whereas the latter
tries to align an electron's spin with its motion.
"This interplay has recently attracted a lot of interest, since it could
lead to the emergence of novel electronic and spin phases, which may be used
in future quantum technologies," says Maryenko. "It is thus important to
understand the fundamentals of the interplay." But it is incredibly
difficult to identify both effects at the same time.
Now, Maryenko and his colleagues have succeeded in disentangling the two
effects.
They looked at electrons trapped between two semiconductors, magnesium zinc
oxide and zinc oxide. Since the system had very few atomic impurities, there
was a strong interaction between electrons. And the researchers could
control the strength of the spin–orbit coupling by varying the magnesium
content. "We looked carefully at how the sample resistance changed when we
applied a magnetic field," says Maryenko. In this way, they were able to
identify signatures of both spin–orbit and the mutual repulsion due to the
electrons' charges.
This high-quality material system thus represents a great resource for
testing theoretical predictions and it opens a path to develop spintronic
phenomena in strong-electron-correlation regimes.
Reference:
D. Maryenko et al, Interplay of spin–orbit coupling and Coulomb interaction
in ZnO-based electron system, Nature Communications (2021).
DOI: 10.1038/s41467-021-23483-4
Tags:
Physics