Special Condensed Matter Seminar: Prof. Lu Li, University of Michigan

The observations of the Landau Level quantizations in narrow-gapped correlated Kondo insulators raise intriguing questions on the origins [1, 2, 3]. However, none of the models suggest the phenomena existing in wide-gap insulators. Kagome lattice Mott insulator Herbertsmithite is a well-established Dirac fermion spin liquid candidate. Yet, our search for magnetic oscillations in Herbertsmithite yielded only a series of magnetic transitions [4], possibly due to the ion disorders on the kagome lattice. This problem is resolved in the recently discovered sibling compound YCu3(OH)6.5Br2.5 [5]. Using ultrasensitive magnetometry on the kagome Mott insulator YCu3(OH)6.5Br2.5 in 70 T intense fields, we observe both the 1/3-plateau and 1/9-plateau transitions. Even more surprisingly, the magnetometry reveals strong oscillations in the magnetic torque. While the temperature dependence follows the Fermi liquid theory, the oscillations appear to be roughly periodic in the magnetic field B, opposite to the 1/B trend in conventional metals. Furthermore, a strong angular dependence is observed for the oscillation fields, which indicates the orbital effect. Separating the orbital effect and the Zeeman effect, we further show that this magnetic oscillation pattern is consistent with a Dirac fermion existing near the 1/9 plateau, and the fermion’s chemical potential is shifted by the Zeeman effect [6].

[1] Xiang, Z. et al., Science 362, 65 (2018)
[2] Li, Lu et al., Nature Review Physics 2, 463 (2020)

[3] Xiang, Z., et al., Nature Physics 17, 788 (2021)
[4] Asaba, T, et al., Physical Review B 90, 064417(2014)
[5] Zeng, M, et al., Physical Review B 105, L121109 (2022)
[6] Zheng, G. et al., arXiv:2310.07989 (2023)