Title: 121,123Sb NQR as a microscopic probe in Te doped correlated semimetal FeSb2 : emergence of electronic Griffith phase, magnetism and metallic behavior %,
Abstract: $^{121,123}Sb$ nuclear quadrupole resonance (NQR) was applied to
$Fe(Sb_{1-x}Te_x)_2$ in the low doping regime (\emph{x = 0, 0.01} and
\emph{0.05}) as a microscopic zero field probe to study the evolution of
\emph{3d} magnetism and the emergence of metallic behavior. Whereas the NQR
spectra itself reflects the degree of local disorder via the width of the
individual NQR lines, the spin lattice relaxation rate (SLRR) $1/T_1(T)$ probes
the fluctuations at the $Sb$ - site. The fluctuations originate either from
conduction electrons or from magnetic moments. In contrast to the semi metal
$FeSb_2$ with a clear signature of the charge and spin gap formation in
$1/T_1(T)T ( \sim exp/ (\Delta k_BT) ) $, the 1\% $Te$ doped system exhibits
almost metallic conductivity and a almost filled gap. A weak divergence of the
SLRR coefficient $1/T_1(T)T \sim T^{-n} \sim T^{-0.2}$ points towards the
presence of electronic correlations towards low temperatures wheras the
\textit{5\%} $Te$ doped sample exhibits a much larger divergence in the SLRR
coefficient showing $1/T_1(T)T \sim T^{-0.72} $. According to the specific heat
divergence a power law with $n\ =\ 2\ m\ =\ 0.56$ is expected for the SLRR.
Furthermore $Te$-doped $FeSb_2$ as a disordered paramagnetic metal might be a
platform for the electronic Griffith phase scenario. NQR evidences a
substantial asymmetric broadening of the $^{121,123}Sb$ NQR spectrum for the
\emph{5\%} sample. This has purely electronic origin in agreement with the
electronic Griffith phase and stems probably from an enhanced $Sb$-$Te$ bond
polarization and electronic density shift towards the $Te$ atom inside
$Sb$-$Te$ dumbbell.