Observation of transition from semiconducting to metallic ground state in high-quality single crystalline FeSi

TL;DR

This study reveals a transition from semiconducting to metallic behavior in high-quality FeSi crystals at low temperatures, with evidence suggesting the emergence of a surface conducting state without bulk magnetic order.

Contribution

It provides detailed experimental evidence of a temperature-induced electronic transition in FeSi, highlighting surface conduction phenomena in a correlated electron system.

Findings

Transition from semiconducting to metallic-like behavior at ~19 K

Sign change in Hall coefficient and magneto-resistivity below 67 K

No bulk magnetic order detected near transition temperatures

Abstract

We report anomalous physical properties of single-crystalline FeSi over a wide temperature range 1.8-400 K. X-ray diffraction, specific heat, and magnetization measurements indicate that the FeSi crystals synthesized in this study are of high quality with a very low concentration of magnetic impurities ($\sim$0.01$\%$). The electrical resistivity $\rho$($T$) can be described by activated behavior with an energy gap $\Delta$ = 57 meV between 67 K and 150 K. At temperatures below 67 K, $\rho$($T$) is significantly lower than an extrapolation of the activated behavior, and the Hall coefficient and magneto-resistivity undergo a sign change in this region. At $\sim$19 K, a transition from semiconducting to metallic-like behavior is observed with deceasing temperature. Whereas the transition temperature is very robust in a magnetic field, the magnitude of the resistivity below $\sim$30 K is very sensitive to magnetic field. There is no indication of a bulk phase transition or onset of magnetic order in the vicinity of either 67 K or 19 K from specific heat and magnetic susceptibility measurements. These measurements provide evidence for a conducting surface state in FeSi at low temperatures.