Insulator-conductor material discovered
Researchers have identified a material that behaves as a conductor and an insulator at the same time, challenging the current understanding of how materials behave, and pointing to a new type of insulating state.
According to the study led by the UK’s University of Cambridge and part-funded by the European Research Council, scientists have discovered mysterious behaviour of a material that acts like an insulator in certain measurements, but simultaneously acts like a conductor in others.
The duelling metal-insulator properties were observed throughout the interior of the material called samarium hexaboride (SmB6). In order to learn more about SmB6 and various other materials, researchers traced the path that the electrons take as they move through the material. The geometrical surface traced by the orbits of the electrons leads to a construction that is known as a Fermi surface. In order to find the Fermi surface, the researchers used a technique based on measurements of quantum oscillations, which measure various properties of a material in the presence of a high magnetic field to get an accurate ‘fingerprint’ of the material. For quantum oscillations to be observed, the materials must be as close to pure as possible, so that there are minimal defects for the electrons to bump into.
Tim Murphy, the head of the National High Magnetic Field Laboratory’s DC Field Facility in Tallahassee, Florida, United States, where most of the research was conducted, said: “This work on SmB6 provides a vivid and exciting illustration of emergent physics resulting from MagLab researchers refining the quality of the materials they study, and pushing the sample environment to the extremes of high magnetic fields and low temperatures.”
At the very lowest temperatures approaching 0 degrees Kelvin (-273°C), it became clear that the quantum oscillations for SmB6 are not characteristic of a conventional metal. In the case of SmB6, the amplitude of quantum oscillations continues to grow dramatically as the temperature is lowered, violating the rules that govern conventional metals.
The researchers considered several reasons for this peculiar behaviour: it could be a novel phase, neither insulator nor conductor; it could be fluctuating back and forth between the two; or because SmB6 has a very small ‘gap’ between insulating and conducting behaviour, perhaps the electrons are capable of jumping that gap.
The results are published in full in the journal Science.
