This is a depiction of the quantum Hall effect (left) and the quantum anomalous Hall effect (right). Credit: RIKEN |
A
team of researchers at RIKEN and the University of Tokyo has
demonstrated a new material that promises to eliminate loss in
electrical power transmission. The surprise is that their methodology
for solving this classic energy problem is based upon the first
realization of a highly exotic type of magnetic semiconductor first
theorized less than a decade ago—a magnetic topological insulator
(“Dirac-fermion-mediated ferromagnetism in a topological insulator”).
Development
of energy saving technologies is one of the central pursuits of modern
science. From advancing alternative energy resources like wind and solar
power to improving the infrastructure of the electrical power grid,
this pursuit by scientists and engineers takes on a variety of forms.
One focus in recent years has been eliminating energy loss in the
transmission of power itself, which by some estimates consumes more than
10% of all energy being produced. The research team has demonstrated a
new material—a magnetic topological insulator—that can eliminate
this loss.
Magnetic topological insulator
At
left, the active area of magnetic topological insulator (dark gray) is 3
micrometers across and only 70 atoms thick. The blue background is an
insulating gate dielectric and the yellow regions are metallic
electrodes. At right, the internal magnet favors the “off” state of the
transistor on the left. This is evidence for a new type of magnetic
semiconductor.
The
work by the RIKEN/UT collaboration is closely related at a landmark
discovery from the 1980s, the so-called quantum Hall effect. That effect
is known to produce dissipationless electricity channels, but it
requires large, cumbersome magnets to produce fields 100,000 larger than
the earth’s magnetic field for its operation.
The
RIKEN/UT collaboration circumvented this difficulty by using an exotic
type of semiconductor predicted to exhibit a similar effect. In contrast
to the quantum Hall effect, this effect, known as the quantum anomalous
Hall effect, stems from the semiconductor’s own magnetization rather
than from an external one. At the heart of this new phenomenon is the
interaction between magnetic ions and the topological insulator’s
current carrying particles (known as Dirac fermions), the latter of
which are unique because they behave as if they have zero mass.
Magnetic surface
This
is a depiction of realization of edge modes on sample surface. At left,
a schematic representation of magnetic structure is shown, dark and
light representing down and up polarization, respectively. At right, the
corresponding edge mode structure is shown, with the green arrows
representing chiral modes at magnetic reversal. The electrical current
flows in the same manner as in the quantum Hall and anomalous quantum
Hall states.
The
devices produced by the RIKEN/UT team are a robust “proof of
principle”, demonstrating that this new type of dissipationless
transport can be harnessed in prototype transistors. While currently
requiring cryogenic conditions, improvements in materials design
promises to improve the stability of the magnets, making it possible to
operate them at higher temperatures. By doing away with external stimuli
such as magnetic fields and, in the future, cryogenic cooling, these
new magnetic topological insulators may represent the most efficient
path to modernizing the power grid by eliminating loss in energy
transfer.
Source: RIKEN