Insulators occur in more than one guise, a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behaviour.
@article{arxiv.1507.01129,
title = {Unconventional Fermi surface in an insulating state},
author = {B. S. Tan and Y. -T. Hsu and B. Zeng and M. Ciomaga Hatnean and N. Harrison and Z. Zhu and M. Hartstein and M. Kiourlappou and A. Srivastava and M. D. Johannes and T. P. Murphy and J. -H. Park and L. Balicas and G. G. Lonzarich and G. Balakrishnan and Suchitra E. Sebastian},
journal= {arXiv preprint arXiv:1507.01129},
year = {2015}
}