Hall-bar device on solid proton
conductor used for measurements. Credit: FLEET
A
Chinese-Australian collaboration has demonstrated for the first time that
interlayer coupling in a van der Waals (vdW) material can be largely modulated
by a protonic gate, which inject protons to devices from an ionic solid.
The
discovery opens the way to exciting new uses of vdW materials, with insertion
of protons an important new technique, now available for the wider 2-D
materials research community.
The study
was led by FLEET researchers at RMIT, in an ongoing collaboration with FLEET
partner organization High Magnetic Field Laboratory, Chinese Academy of
Sciences (CAS).
Tuning
interlayer forces in van der Waals materials
Van der
Waals materials, of which graphite is the most famous, are made of many 2-D
layers held together by weak, electrostatic forces.
Individual
layers of vdW materials can be isolated individually, such as the famous Scotch
tape method of producing graphene, or stacked with other materials to form new
structures.
"But
the same weak interlayer forces that make vdW materials so easy to separate
also limit these materials' applications in future technology," explains
the study's first author, FLEET Research Fellow Dr. Guolin Zheng.
Stronger
interlayer coupling in vdW materials would significantly increase potential use
in high-temperature devices utilizing quantum anomalous Hall effect, and in 2-D
multiferroics.
The new
RMIT-led study demonstrated that coupling in a vdW material, Fe3GeTe2 (FGT) nanoflakes,
can be largely modulated by a protonic gate.
With the
increase of the protons among layers, interlayer magnetic coupling increases.
"Most
strikingly, with more protons inserted in FGT nanoflakes at a higher gate
voltage, we observed a rarely seen zero-field cooled exchange bias with very
large values," says co-author A/Prof Lan Wang.
The
successful realization of both field-cooled and zero-field cooled exchange bias
in FGT implies the interlayer coupling can be largely modulated by gate-induced
proton insertion, opening the road to many applications of vdW materials
requiring strong interface coupling.