(September 15, 2015) An international group of physicists, including Aleksandr
Golubov, head of the MIPT Laboratory of Topological Quantum Phenomena in
Superconductor Systems, recently presented results of experiments testing a new
phenomenon in the journal Science. The results may assist scientists in the
creation of an essentially new kind of electronics - Mott transition, or the
transition of an insulator to a conductor.
Researchers from institutions in the Netherlands, Great
Britain, Italy, the USA and Russia conducted a series of experiments with Mott
insulators. These materials, according to band theory,* should be conductors
but, in practice, are dielectrics (insulators). In general terms, the mechanism
behind this anomaly is known to physicists, though a complete theory for Mott
insulators does not yet exist. They do not fully understand how the materials
transform from insulators into conductors.
* Band theory is a quantum theory developed in the first
half of the 20th century to explain the electrical properties of substances.
The theory is based on the idea of quantum energy states. Electrons in a
substance either have both sufficient energy and free transition and, thus, are
able to enter the zone of conductivity, or they do not, in which case it
becomes what researchers call a “forbidden zone.”
At the same time, preliminary estimates indicate that this
effect is capable of opening a new path to faster computers. Motto transition
occurs under the influence of several factors, including a magnetic field,
which allows it to be controlled from outside. This makes it possible for
researchers to permit current flow or to stop it at a necessary point. Such a
scheme could replace common transistors and, in this case, allow them to be
faster and more compact. But to do so, scientists must utilize the theory of
Motto transition.
The theory belongs to fundamental conceptions explaining the
electrical properties of a substance. It has a direct relation not only to
Motto insulator behavior but also to superconductivity and the fundamentals of
spintronics, a technology that could allow the control of electron spin.*
Superconductivity and spintronics are among those trends where one can expect
radical technological breakthrough, which is what makes understanding the nature
of Motto transition so important – and not only from a purely theoretical point
of view.
* Physicists define spin (spin up and spin down) as a
quantum quantity, which “shows itself” when a particle interacts with a
magnetic field. Spin plays a fundamental role in quantum physics because,
without considering spin, it is impossible to describe the behavior of
electrons in atoms, the phenomenon of material magnetization or molecular
structure. The phenomenon of magnetic resistance goes together with spin. This
can be seen when a sample is placed in a magnetic field and its electrical
resistance dramatically changes; the effect is also seen in all modern hard
drives.
In their new research, the physicists used a special model that allowed
them to study quantum processes in the Motto insulator with the aid of
so-called magnetic vortices. In this model, which was proposed by Valery
Vinokur and David Nelson in 1993, electric current actuates a quantum vortex in
a superconducting material, and one can consider such vortices to be the charge
carrier. At this point - which is most significant, and about which Vinokur and
Nelson wrote when discussing phase transitions* in their work - the superconductor with magnetic vortices
behaved either like superfluid liquid or like glass, through which electric
current cannot pass. By varying the temperature and the magnetic field, the
scientists converted the sample from one state to another, and these
observations together with the set of newer data were used as a basis for the
new research.