Nav: Home

One step closer to a new kind of computer

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.

* Phase transitions - transition of a substance from one state to another. A classic example is ice melting and turning into water, or water evaporating to become vapor. The demagnetization of a magnetized needle by heating it with a candle flame, which is an experiment that is also conducted in school, is another example of phase transition. Phase transitions are part of the study of thermodynamics, and they are connected with changes in the characteristics of a system such as total energy, entropy and order.

For the new experiment, the scientists created a quadrangular matrix on a silicon slab from 300?300 niobium "islets" with a diameter of about 220 nanometers and attached gold and niobium contacts to it. They made the sample using standard photolithograph methods, and then placed it in a cryostat, allowing it to cool to 1.4 kelvins, which is lower than the temperature needed for niobium to transition to a superconducting state. The niobium islets became superconductors, magnetic vortexes formed in them, and the researchers then analyzed the behavior of the system in different conditions.

Pic. The matrix made from niobium islets used in the experiments, its relief and cross-section, as well as a general view (C) in the optical microscope. Illustration courtesy of the researchers.

In particular, they measured the sample resistance and discovered that this quantity changes nonlinearly with an increasing magnetic field. From a theoretical point of view, the results suggest that one can view Motto transition as the transition of a substance from a liquid state to a gas, which opens up additional opportunities for analyzing the phenomenon from the perspective of thermodynamics. The experimental scheme developed by the scientists makes further experiments comparatively simple, because they have a sufficient amount of photolithograph methods and temperatures comparable with the temperature of liquid helium. It is worth noting that the low temperatures were achieved without the use of expensive liquid helium, and last year MIPT installed a similar unit in the laboratory at the Interdisciplinary Center for Basic Research.

Nonlinear resistance of the sample and the influence of magnetic fields upon electrical resistance. Illustration courtesy of the researchers.
-end-
The article has been published in the journal Science and is available at arxiv.org.

Link to the article: http://www.sciencemag.org/content/349/6253/1202

It is signed by researchers from Twente University (the Netherlands, second place of employment for Aleksandr Golubov), Rome International Center for Materials Science Center RICMASS, the Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk State University, Argonne National Laboratory (the USA), Queen Mary University of London, and MIPT.

Moscow Institute of Physics and Technology

Related Magnetic Field Articles:

Earth's last magnetic field reversal took far longer than once thought
Every several hundred thousand years or so, Earth's magnetic field dramatically shifts and reverses its polarity.
A new rare metals alloy can change shape in the magnetic field
Scientists developed multifunctional metal alloys that emit and absorb heat at the same time and change their size and volume under the influence of a magnetic field.
Physicists studied the influence of magnetic field on thin film structures
A team of scientists from Immanuel Kant Baltic Federal University together with their colleagues from Russia, Japan, and Australia studied the influence of inhomogeneity of magnetic field applied during the fabrication process of thin-film structures made from nickel-iron and iridium-manganese alloys, on their properties.
'Magnetic topological insulator' makes its own magnetic field
A team of U.S. and Korean physicists has found the first evidence of a two-dimensional material that can become a magnetic topological insulator even when it is not placed in a magnetic field.
Scientists develop a new way to remotely measure Earth's magnetic field
By zapping a layer of meteor residue in the atmosphere with ground-based lasers, scientists in the US, Canada and Europe get a new view of Earth's magnetic field.
Magnetic field milestone
Physicists from the Institute for Solid State Physics at the University of Tokyo have generated the strongest controllable magnetic field ever produced.
New world record magnetic field
Scientists at the University of Tokyo have recorded the largest magnetic field ever generated indoors -- a whopping 1,200 tesla, as measured in the standard units of magnetic field strength.
Researchers discover link between magnetic field strength and temperature
Researchers recently discovered that the strength of the magnetic field required to elicit a particular quantum mechanical process corresponds to the temperature of the material.
Astronomers observe the magnetic field of the remains of supernova 1987A
For the first time, astronomers have directly observed the magnetism in one of astronomy's most studied objects: the remains of Supernova 1987A (SN 1987A), a dying star that appeared in our skies over thirty years ago.
Watch: Insects also migrate using the Earth's magnetic field
A major international study led by researchers from Lund University in Sweden has proven for the first time that certain nocturnally migrating insects can explore and navigate using the Earth's magnetic field.
More Magnetic Field News and Magnetic Field Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.