Doping effects on the hybridization gap and antiferromagnetic order in the Kondo semiconductor CeOs2Al10 studied by break-junction experiments

Abstract

The Kondo semiconductors $\mathrm{Ce}{T}_{2}\mathrm{A}{\mathrm{l}}_{10}$ ($T=\mathrm{Ru}$ and Os) exhibit antiferromagnetic (AFM) orders at unexpectedly high temperatures ${T}_{\mathrm{N}}=27.0$ and 28.5 K, respectively, whose mechanism remains in debate. We report the break-junction experiments on $4f/5d$-hole and $5d$-electron doped $\mathrm{CeO}{\mathrm{s}}_{2}\mathrm{A}{\mathrm{l}}_{10}$ as well as nondoped $\mathrm{CeR}{\mathrm{u}}_{2}\mathrm{A}{\mathrm{l}}_{10}$. The differential conductance spectra $dI/dV$ for $T=\mathrm{Os}$ and Ru show three gap structures; two hybridization gaps ${V}_{1}, {V}_{2}$ and an AFM gap ${V}_{\mathrm{AF}}$, whose magnitudes for $T=\mathrm{Os}$ are $15\ensuremath{-}50%$ larger than for $T=\mathrm{Ru}$. Doping of $4f/5d$ holes and $5d$ electrons in $\mathrm{CeO}{\mathrm{s}}_{2}\mathrm{A}{\mathrm{l}}_{10}$ changes the $dI/dV$ spectrum in very different ways. Nevertheless, in all cases, the suppression of ${V}_{1}$ is well correlated with those of ${V}_{\mathrm{AF}}$ and ${T}_{\mathrm{N}}$. Furthermore, the zero-bias conductance decreases on cooling below ${T}^{*}$ ($g{T}_{\mathrm{N}}$) only in the doping region where ${V}_{1}$ and ${V}_{\mathrm{AF}}$ coexist. This fact indicates that the unusual AFM order is preceded by the decrease in the density of states in the presence of ${V}_{1}$.