Speaker
Description
The de Haas-van Alphen (dHvA) effect has long been regarded as a definitive signature of a metal, because the theory is formulated in terms of the emptying of quantized Landau levels as they pass through the Fermi surface. In this picture, there should be no oscillatory magnetization in an insulator because there is no Fermi surface for the Landau levels to cross. Thus, the observation of dHvA oscillations in the Kondo insulator SmB$_6$ [1, 2] was a surprise. Almost equally surprising, a possible, very simple, theory of these quantum-oscillations-without-a-Fermi-surface was soon found: Knolle and Cooper [3] showed that quantum oscillations emerge in a straightforward calculation of the thermodynamic potential of a narrow-gap insulator with Landau-quantized states. The physical origin of these oscillations was, however, unclear, and a source of some confusion. The purpose of this somewhat pedagogical talk is to present a simple semiclassical picture that shows that the anomalous Knolle-Cooper dHvA oscillations in hybridzation gap insulators are produced by the sudden change in the diamagnetic moment of the Landau levels as they pass between regions of the valence band that have different quasiparticle velocities.Thus, nearly 100 years after the first prediction and observation of de Haas van Alphen oscillations, a qualitatively new mechanism for these oscillations has been found.
[1] G. Li, Z. Xiang, F. Yu, T. Asaba, B. Lawson, P. Cai, C. Tinsman, A. Berkley, S. Wolgast, Y. S. Eo, D.-J. Kim, C. Kurdak, J. W. Allen, K. Sun, X. H. Chen, Y. Y. Wang, Z. Fisk, and L. Li, Science 346, 1208 (2014).
[2] B. S. Tan, Y.-T. Hsu, B. Zeng, M. Ciomaga Hatnean, N. Harrison, Z. Zhu, M. Hartstein, M. Kiourlappou, A. Srivastava, M. D. Johannes, T. P. Murphy, J.-H. Park, L. Balicas, G. G. Lonzarich, G. Balakrishnan, and S. E. Sebastian, Science 349, 287 (2015).
[3] J. Knolle and N. R. Cooper, Phys. Rev. Lett. 115, 146401 (2015)
[4] some of the content of this talk was published in S. R. Julian, Canadian Journal of Physics 101, 393 (2023)
| Keyword-1 | quantum materials |
|---|---|
| Keyword-2 | electronic structure |
| Keyword-3 | topological insulators |