Bulk Rotational Symmetry Breaking in Kondo Insulator SmB₆

In Kondo insulators the insulating behavior is introduced by the interaction between localized and conduction electrons at low temperature. Theories predicted that Kondo insulator is a promising candidate of strongly electron correlated topological insulator. The de Haas-van Alphen (dHvA) effect, i.e., oscillation in magnetization generated by the energy quantization of conduction electrons in magnetic field, has been observed in the insulating phase of samarium hexaboride (SmB₆), a typical Kondo insulator. Intense debate has been put on the origin of the dHvA oscillations. We measured the dHvA signal using torque magnetometry in SmB₆ single crystals. Besides the 2D-like angular dependence of dHvA oscillation frequencies, the angle-dependent amplitude breaks the 4-fold rotational symmetry of the cubic crystal structure. The angular and temperature dependence of dHvA amplitudes are both consistent with the behavior of a 2D Fermi liquid system down to 40 mK and up to 45 T [1]. Our results demonstrate the existence of 2D electronic states with light quasiparticle mass in SmB₆, which are consistent with the interpretation of topologically protected surface states.

[1] Z. Xiang, B. Lawson, T. Asaba, C. Tinsman, L. Chen, C. Shang, X. H. Chen, Lu Li, Physical Review X 7, 031054 (2017).