Scanning tunneling microscopes capture images of materials with atomic
precision and can be used to manipulate individual molecules or atoms.
Researchers have been using the instruments for many years to explore the
world of nanoscopic phenomena. A new approach by physicists at
Forschungszentrum Jülich is now creating new possibilities for using the
devices to study quantum effects. Thanks to magnetic cooling, their scanning
tunneling microscope works without any moving parts and is almost
vibration-free at extremely low temperatures as low as 30 millikelvin. The
instrument can help researchers unlock the exceptional properties of quantum
materials, which are crucial for the development of quantum computers and
sensors.
Physicists consider the temperature range near absolute zero to be a
particularly exciting area for research. Thermal fluctuations are reduced to
a minimum. The laws of quantum physics come into play and reveal special
properties of materials. Electric current then flows freely without any
resistance. Another example is a phenomenon called superfluidity: Individual
atoms fuse into a collective state and move past each other without
friction.
These extremely low temperatures are also required to research and harness
quantum effects for quantum computing. Researchers worldwide as well as at
Forschungszentrum Jülich are currently pursuing this goal at full speed.
Quantum computers could be far superior to conventional supercomputers for
certain tasks. However, development is still in its infancy. A key challenge
is finding materials and processes that make complex architectures with
stable quantum bits possible.
"I believe a versatile microscope like ours is the tool of choice for this
fascinating task, because it enables matter to be visualized and manipulated
at the level of individual atoms and molecules in many different ways,"
explains Ruslan Temirov from Forschungszentrum Jülich.
Over years of work, he and his team have equipped a scanning tunneling
microscope with magnetic cooling for this purpose. "Our new microscope
differs from all the others in a similar way to how an electric car differs
from a vehicle with a combustion engine," explains the Jülich physicist.
Until now, researchers have relied on a kind of liquid fuel, a mixture of
two helium isotopes, to bring microscopes to such low temperatures. "During
operation, this cooling mixture circulates continuously through thin pipes,
which leads to increased background noise," says Temirov.
The cooling device of Jülich's microscope, on the other hand, is based on
the process of adiabatic demagnetization. The principle is not new. It was
used in the 1930s to reach temperatures below 1 kelvin in the laboratory for
the first time. For the operation of microscopes, it has several advantages,
says Ruslan Temirov: "With this method, we can cool our new microscope just
by changing the strength of the electric current passing through an
electromagnetic coil. Thus, our microscope has no moving parts and is
practically vibration-free."
The Jülich scientists are the first ever to have constructed a scanning
tunneling microscope using this technique. "The new cooling technology has
several practical advantages. Not only does it improve the imaging quality,
but the operation of the whole instrument and the entire setup are
simplified," says institute director Stefan Tautz. Thanks to its modular
design, the Jülich quantum microscope also remains open to technical
advances, he adds, as upgrades can be easily implemented.
"Adiabatic cooling is a real quantum leap for scanning tunneling microscopy.
The advantages are so significant that we are now developing a commercial
prototype as our next step," Stefan Tautz explains. Quantum technologies are
currently the focus of much research. The interest of many research groups
in such an instrument is therefore assured.
Teh research was published in Review of Scientific Instruments.
Reference:
Taner Esat et al, A millikelvin scanning tunneling microscope in ultra-high
vacuum with adiabatic demagnetization refrigeration, Review of Scientific
Instruments (2021).
DOI: 10.1063/5.0050532
Tags:
Physics