Double Standard/How to Pass Current through Rusty:

Physicists Discover a Fundamentally New State of Matter at Ultra-High Pressures

In order to find a new explanation for the generally accepted scientific postulate, especially a Nobel-awarded a truly breakthrough discovery is needed. Such a discovery was made by an international research group of scientists from NUST MISIS, Ural Branch of RAS, Tel Aviv University, University of Bayreuth and Linköping University. This concerns a remarkable phenomenon, which physicists first observed at the beginning of the last century. Iron oxide (hematite), which is dielectric, surprisingly transits into a good conductor at a pressure of about 1 million atmospheres. Why is there such a phase transition of matter from one state to another? For decades, scientists tried to find an explanation. Finally, a British scientist Neville Francis Mott managed to do this, which brought him a Nobel Prize in 1977. But what problems did modern scientists find in the laureate’s theory?

An international team of physicists from NUST MISIS, Ural Branch of RAS, Tel Aviv University, University of Bayreuth and Linköping University found a completely new explanation of one of the common physical postulates — phase dielectric-metal transition, described in 1949 by Sir Neville Francis Mott. Novel and surprising material properties discovered in the study will be in demand in microelectronics and geophysics as catalysts and sensors; the results are published in Physical Review X.

A classic of modern physics, Sir Neville Mott was the first to describe how material is transformed from dielectric to conductor, and received the Nobel prize in 1977.

Since that, the scheme was considered classical and was mandatory for studying by all scientists.

But recently the abovementioned group of scientists discovered a completely new scheme of phase transition named space-selective Mott transition.

The research team worked with a dielectric material, hematite or iron oxide Fe2O3 (this is rust which does not conduct current at all). Scientists placed the material in a diamond anvil and compressed it at ultra-high pressures of up to 100 GPa (up to 1 million atmospheres). At such extreme external conditions hematite-dielectric transits into conductor.

Hematite is one of the “classical” Mott’s dielectrics. The description of its properties is of a fundamental interest both to understand the physics of various magnetic-structural transformations near the metallization of the system under pressure (in magnetic / electric fields, doping, etc.) and geology (geochemistry and geophysics), as Fe2O3 is one of the most common compounds of the Earth’s interior.

The main surprise of the result is that at ultra-high pressures TWO crystal lattices appear in a single-crystal Fe2O3. At the same time, the material shows the properties of metal (conductor) and a dielectric. A complicated magnetic-structural transition leading to the formation of two iron sublattices with fundamentally different properties.

“Briefly speaking, in the context of the research (theoretical and practical) of Fe2O3 properties at ultra-high pressure, a fundamentally new explanation of dielectric-metal Mott transition was suggested, — Ivan Leonov, co-author, NUST MISIS researcher, Sc.D. in Physics and Mathematics, explains — From the fundamental point of view, we have described a new class of phase transitions in compounds with strong correlations (this is a large class of materials that includes high-temperature superconductors based on copper or iron, compounds with colossal magnetoresistance, ferroelectrics, magnets, etc.); in fact, a new state of matterial was described, characterized by both metal and dielectric properties”.

Figure 1. In normal dielectric condition hematite has a prismatic lattice; at a pressure of 50 GPA, it becomes a conductor, while two iron sublattices containing octahedra and prisms are observed.

The results of the study are important for understanding the physical processes in the lower mantle of the Earth. In addition, the described properties of the new state of matter will certainly be interesting for microelectronics, as well as for creating innovative sensors or switches in the aircraft industry, in space and automotive industries.

Figure 2. Earth internal structure.