Physicists
at the University of New South Wales have observed a new kind of
interaction that can arise between electrons in a single-atom silicon
transistor.
The findings, to be published this week in the journal Physical Review Letters, offer a more complete understanding of the mechanisms for electron transport in nanostructures at the atomic level.
“We
have been able to study some of the most complicated transport
mechanisms that can arise up to the single atom level,” says lead author
Dr Giuseppe C. Tettamanzi, from the School of Physics at UNSW.
The
results contained in this study open the door for new quantum
electronic schemes in which it is the orbital nature of the
electrons—and not their spin or their charge—that plays a major role, he
says.
The
study, in collaboration with scientists from the ICMM in Madrid and the
Kavli Institute in The Netherlands, describes how a single electron
bound to a dopant atom in a silicon matrix can interact with many
electrons throughout the transistor.
In
these geometries, electron-electron interactions can be dominated by
something called the Kondo effect. Conventionally, this arises from the
spin degree of freedom, which represents an angular momentum intrinsic
to each electron and is always in the up or in the down state.
However,
researchers also observed that similar interactions could arise through
the orbital degree of freedom of the electron. This describes the
wave-like function of an electron and can be used to help determine an
electrons’ probable location around the atom’s nucleus.
Importantly,
by applying a strong magnetic field, the researchers were able to tune
this effect to eliminate the spin-spin interactions while preserving the
orbital-orbital interactions.
“By
tuning the effect in two different symmetries of the fundamental state
of the system…we have observed a symmetry crossover identical to those
seen in high-energy physics,” says Tettamanzi.
“In
our case this crossover was observed simply by using a semiconductor
device which is not too different from the transistor you use daily to
send your emails.”
Tettamanzi,
who was recently awarded a prestigious ARC Discovery Early Career
Researcher Award fellowship, will now investigate another transport
mechanism that can arise in quantum dots and single atom transistors
called “quantised charge pumping”.
The
idea here is to create a current flowing through a nanostructure
without applying a voltage between the leads, but by applying varying
potentials at one or more gates of the transistor, in an apparent
violation of Ohm’s law.
