First, some background
When it comes to conducting electricity, some materials are better than others. Generally, materials are considered either conductors (like copper) or insulators (wood, for example). Some materials, however, don’t fall so neatly into one category or the other, and they tend to be of particular interest to scientists. Nickel disulfide (NiS2) is one such material. It is known as a Mott insulator: Even though its structure suggests that electrons should move through it to conduct electricity if a voltage is applied, it is in fact an insulator. Its electrons are stuck in place due to how they interact with one another.
What did scientists discover?
Scientists can sometimes change a material’s conductive/insulating state by changing its environment — changing the ambient temperature or pressure, for example, or introducing a magnetic field. When they put NiS2 under high pressure in a high magnetic field, electrons that had been in virtual gridlock were liberated: The material converted from an insulator, (think plastic), into a conductor, like a metal.
Of particular interest to the scientists was how those electrons moved. In conventional electricity, electrons move as individual particles. But in the NiS2, the electrons were influencing each other as they moved, advancing not as individuals, but as a system. Scientists call this behavior "highly correlated."
Scientists are especially interested in this kind of behavior because it’s exhibited by some high-temperature superconductors (HTS). HTS materials, which conduct electricity with perfect efficiency at relatively high temperatures, are of intense interest among physicists.
Why is this important?
Some scientists speculate that understanding this complex state of matter holds the key to engineering HTS materials that work at higher temperatures. The higher that temperature, the closer we are to being able to use HTS materials for energy and other applications that could revolutionize the power industry.
Who did the research?
H. Chang1, S. Friedemann1,2, A. Grockowiak3, W. Coniglio3, K. Semeniuk1, J. Baglo1, S. Tozer3, F. M. Grosche1
1University of Cambridge, UK; 2University of Bristol, UK; 3MagLab Tallahassee
Why did they need the MagLab?
The scientists did measurements for which the signal increases exponentially with the strength of the magnetic field. University laboratories do not offer sufficiently high magnetic fields for this experiment. The study also relied on pioneering high pressure techniques developed at the MagLab.
Details for scientists
- View or download the expert-level Science Highlight, Pressure converts an insulator into a metal with enhanced electronic mass
- Read the full-length publication, Large Fermi surface of heavy electrons at the border of Mott insulating State in NiS2, in Scientific Reports.
This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); Chang, Friedemann, Semeniuk, Baglo and Grosche (EPSRC EP/K012894/1); Friedemann (EU Marie Curie fellowship 271982)
For more information, contact Tim Murphy.