Optical Evidence of Anderson-Mott Localization in FeSi

Abstract

Anderson-Mott localization behaviour of the low-temperature optical conductivity, while at high frequencies the excitation spectrum resembles that of a conventional semiconductor. The missing spectral weight below the gap energy is redistributed around the gap edge, in disagreement with previous claims based on optical measurements.

Tunneling spectroscopy on the correlation effects in FeSi

“…Another unusual feature that also suggests the presence of strong correlations in FeSi is that the spectral weight expelled from the gap region is spread over a frequency range more than 1 eV above the gap. The results by DeGiorgi et al 36 are in disagreement with those findings, but as was noted earlier their sample is apparently more metallic and probably not representative for the intrinsic behavior of FeSi. 19 We, therefore, compare our results below to those obtained by Damascelli et al 22 who performed their measurements on the same high-quality single crystals that we used for tunneling spectroscopy.…”

Spin, charge, and bonding in transition metal mono-silicides

“…We see, that for CoSi the N m e /m * (ω)-curves for different temperatures merge above 1000 cm −1 indicating that no transfer of spectral weight from high to low frequencies takes place. For FeSi the recovery of spectral weight can be followed upto approximately 2000 cm −1 above which the experimental errorbars become rather large as a result of uncertainties in the KramersKronig analysis, mainly induced by the extrapolations at high frequency [9,10]. It seems plausible to associate the temperature dependence of the section between 1000 and 2000 cm −1 with the optical conductivity due to thermally induced charge carriers.…”

Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir, Delaire1, Al-Qasir2, May3 et al. 2015Phys. Rev. B412190View full textAdd to dashboardCite

“…In addition, it has been shown that phonon excitations at finite temperature can close the narrow gap, accounting for some of the observed anomalous temperature dependences [24][25][26][27][28][29][30] , in particular the experimental observation of the gap closing [31][32][33] . Possibly strong electronic correlations have also be noted 34,35 , and it has been proposed that that FeSi could be an unusual d−electron Kondo insulator, although this point remains controversial 32,34,[36][37][38][39] . Interest in FeSi also arises from geophysics, as it is a possible reaction product between molten iron and mantle silicates at the core-mantle boundary 14,[40][41][42] .…”