6533b85bfe1ef96bd12bbd81

RESEARCH PRODUCT

Robust hybridization gap in the Kondo insulator YbB12 probed by femtosecond optical spectroscopy

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description

In heavy fermions the relaxation dynamics of photoexcited carriers has been found to be governed by the low energy indirect gap ${\mathrm{E}}_{g}$ resulting from hybridization between localized moments and conduction band electrons. Here, carrier relaxation dynamics in a prototype Kondo insulator $\mathrm{Yb}{\mathrm{B}}_{12}$ is studied over a large range of temperatures and over three orders of magnitude. We utilize the intrinsic nonlinearity of dynamics to quantitatively determine microscopic parameters, such as electron-hole recombination rate. The extracted value reveals that hybridization is accompanied by a strong charge transfer from localized $4f$ levels. The results imply the presence of a hybridization gap up to temperatures of the order of ${\mathrm{E}}_{g}/{\mathrm{k}}_{B}\ensuremath{\approx}200$ K, which is extremely robust against electronic excitation. Finally, below 20 K the data reveal changes in the low energy electronic structure, attributed to short-range antiferromagnetic correlations between the localized levels.