Metal or Insulator?

A team including Warwick authors Geetha Balakrishnan and Monica Ciomaga Hatnean have discovered the existence of an unusual insulating state in SmB₆. SmB₆ is a well studied Kondo Insulator with interesting conduction properties, and it has recently been proposed that it may be a Topological Insulator (i.e., bulk insulators which exhibit exotic surface conduction properties). The unusual insulating state was inferred from the observation of quantum oscillations (undulations in properties such as resistance and magnetization as the magnetic field is swept) in the measurements of the magnetic torque at high magnetic fields on high purity crystals of SmB₆. The key to these observations has been the high quality single crystals prepared for these experiments at Warwick. Quantum oscillations are inherently a property of metals, where they map out the Fermi surface. These observations on SmB₆ which is an insulator at low temperatures, now offers new challenges in explaining both the bulk and surface conduction properties of this intriguing material.

The paper "Unconventional Fermi surface in an insulating state" can be read in full in the online journal Science Express, 2 July 2015, (http://www.sciencemag.org/content/early/recent ahead of it being published in “Science”.