Evidence for a conducting surface state in FeSi*

Electrical transport measurements on high quality single crystals of FeSi show a crossover from semiconducting to metallic behavior at 19 K (T_c). This metallic temperature dependent resistivity points to a conducting surface ground state of FeSi, supported by the impact of surface-to-volume ratio on the resistivity of the sample, and the absence of features in specific heat at low temperature [1]. We further explore this surface state using high field magnetoresistance, high pressure, and magnetic field modulated microwave spectroscopy (MFMMS). Surprisingly, the surface sensitive MFMMS measurement of FeSi shows an anomaly near T_c with a signature typically associated with superconducting transitions. Based on the similarities in magnetoresistance between FeSi and the possible topological Kondo insulator SmB₆, FeSi could be a possible topological insulator.

[1] Y. Fang, S. Ran, W. Xie, S. Wang, Y. Meng, and M. B. Maple, PNAS 117, 8558 (2019)