Magnetoconduction in the Correlated Semiconductor FeSi in Ultrastrong Magnetic Fields up to a Semiconductor-to-Metal Transition

Magnetoresistance of the correlated narrow-gap semiconductor FeSi was investigated by the radio frequency self-resonant spiral coil technique in magnetic fields up to 500 T, which is supplied by an electromagnetic flux compression megagauss generator. Semiconductor-to-metal transition accomplishes around 270 T observed as a sharp kink in the magnetoresistance, which implies the closing of the hybridization gap by the Zeeman shift of band edges. In the temperature-magnetic field phase diagram, the semiconductor-metal transition field is found to be almost independent of temperature, which is in contrast to a characteristic magnetic field associated with the hopping magnetoconduction in the in-gap localized states, exhibiting a notable temperature dependence.

Figure 1

Temperature dependence of dc electrical resistivity measured by PPMS. Two regions of temperature range are divided by a boundary line ($T^{*}=80\mathrm{K}$) on the basis of each transport mechanism. The solid curve is a fitting result of ${\rho }_{\mathrm{dc}}$. An intrinsic band gap and in-gap components of the fitting curve are shown by a dotted and a dashed line, respectively.

Figure 2

Results of the high-field experiments. (a) Time evolution of $V_{\text{rf}}$ (upper panel) and a pulsed magnetic field (lower panel) at 53 K. The inset is a schematic configuration of an FeSi sample and probe coil. (b) Magnetic field dependence of the electrical resistivity at 53 K, 29 K, and 6 K. Characteristic magnetic field intensities $B_{\mathrm{sh}}$, $B_{{\text{S}\text{−}\text{M}}^{’}}$, and $B_{\text{S-M}}$ are pointed by arrows, which are determined by an intersection of light-green dotted tangential lines.

Figure 3

Schematic illustration of the electronic energy bands in a characteristic range of temperatures and magnetic fields, (a) to (d), in accordance with different events of each transport phenomenon. The blue energy levels indicate the midgap states, which dominate the electrical transport phenomenon below $B_{{\text{S}\text{−}\text{M}}^{’}}$ and temperature below $T^{*}$. Symbol $\times$ represents an inactivated transition over the hybridization gap $\mathrm{\Delta }$.

Figure 4

$T–B$ phase diagram of electronic conduction. Thin black dotted lines show the sample temperatures evaluated from calculated Joule heating. The bold dotted (dashed) curves are guidelines of phase boundaries derived from characteristic magnetic field $B_{\mathrm{sh}}$ ($B_{{\text{S-}\text{M}}^{’}}$ and $B_{\text{S-M}}$).