17 September 2015

Insulator or metal … or, somehow, both at the same time?

Examining the material samarium hexaboride, scientists discover seemingly contradictory properties and an exciting, new mystery for physicists.

What did scientists discover?

An insulator is a material that does not conduct electricity: its resistance to electrical flow increases as temperature decreases, as shown in Figure 1. Yet metals become magnetic at low temperatures when subjected to an intense magnetic field — exhibiting an oscillatory amount of magnetization as magnetic field is increased, arising from the freedom of electrons in metals to orbit in response to an intense applied magnetic field, as seen in Figure 2. However, researchers have found a material, samarium hexaboride, that behaves like an insulator and a metal … and its magnetic quantum oscillations are more than five times too big to be explained by any known theory, as shown in Figure 3.

Why is this important?

Samarium hexaboride is apparently both an insulator and a metal … which is a bit like saying something is white and black at the same time. Because we understand simple insulators and metals extremely well, the only possible explanation is that the billions of electrons in samarium hexaboride have found a way to work collectively in some new and surprising way. They exhibit a new, emerging behavior that is neither — or perhaps both — insulator and metal, a strange hybrid that shows properties of each and new, unexpected behaviors never before seen.

Who did the research?

B. S. Tan1, Y.-T. Hsu1, B. Zeng2, M. Ciomaga Hatean3, N. Harrison2, Z. Zhu2, M. Hartstein1, M. Kiourlappou1, A. Srivastava1, M. D. Johannes4, T. P. Murphy2, J.-H. Park2, L. Balicas2, G. G. Lonzarich1, G. Balakrishnan3, Suchitra E. Sebastian1

1University of Cambridge; 2National High Magnetic Field Laboratory; 3University of Warwick; 4Naval Research Laboratory

Why did they need the MagLab?


This research was conducted in the 45 tesla hybrid magnet and the35 tesla resistive magnet at the MagLab's DC Field Facility.

High magnetic fields amplify the quantum oscillations exponentially. For that reason, more quantum oscillations are measured in the greatest variety of materials at the MagLab than anywhere else in the world. This enables researchers to get the best possible understanding of new metallic behaviors or, in this case, to reveal a deep new mystery that remains unexplained.

Details for scientists


This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); S. E. Sebastian (ERC Grant Agreement 337425); L. Balicas (DOE-BES DE-SC0002613); G.Balakrishnan (EPSRC EP/L014963/1); N.Harrison (DOE-BES “Science of 100 Tesla”; G. G. Lonzarich (EPSRC EP/K012894/1).

For more information, contact Tim Murphy.


  • Research Area: Kondo/Heavy Fermion Systems
  • Research Initiatives: Materials
  • Facility / Program: DC Field
  • Year: 2015
Last modified on 6 October 2015