Gap-like feature in the normal state of $\mathbf{X}(\mathbf{F}{\mathbf{e}}_{1-\mathbf{x}}\mathbf{C}{\mathbf{o}}_{\mathbf{x}}{)}_2\mathbf{A}{\mathbf{s}}_2$, $\mathbf{X}=\mathbf{Ba},\mathbf{Sr}$ and $\mathbf{F}{\mathbf{e}}_{1+\mathbf{y}}\mathbf{Te}$ revealed by Point Contact Spectroscopy

Abstract

Point contact spectroscopy reveals a gap-like feature above the magnetic and structural transition temperatures for underdoped $Ba(F{e}_{1-x}C{o}_x{)}_{2}A{s}_2$, $SrF{e}_{2}A{s}_2$ and $F{e}_{1+y}Te$. The conductance spectrum starts showing an enhancement at temperatures as high as 177 K for $BaF{e}_{2}A{s}_2$ ($T_N$ $\sim$ 132 K) and 250 K for $SrF{e}_{2}A{s}_2$ ($T_N$ $\sim$ 192 K). Possible origins for this enhancement are discussed in light of recent experimental claims of nematicity in these materials. We construct a modified phase diagram for Co-doped Ba122 showing a gap-like feature existing above $T_N$ and $T_S$ for the underdoped regime.