Optical investigations of the heavy-fermion superconductor UNi2Al3

Abstract

The optical properties of the heavy-fermion superconductor UNi2Al3 have been investigated at temperatures between 10 and 300 K using reflectance spectroscopy. A characteristic energy scale (ωc=90 cm−1), with almost the same value as the coherence temperature T0=100 K derived from measurements of the dc resistivity and susceptibility, is obtained from the optical conductivity. At high temperatures (T≥T0), this scale represents the energy gap between the ground and excited level that results from the crystal-field splitting of the 5f2 (J=4) level of the tetravalent uranium ion. In the low-temperature coherent region (T<T0), a narrow, Drude-like, quasiparticle absorption mode develops. This mode is described using a frequency-dependent scattering rate Γ(ω) and mass enhancement factor λ(ω). This free-carrier mode may originate from a hybridization between the 3d conduction band of nickel and the 5f bands of uranium. Parameters such as the renormalized scattering rate γ* and plasma frequency ωP* of the quasiparticle mode, as well as the quasiparticle bandwidth W at 10 K are derived using the model developed by Millis and Lee. © 1996 The American Physical Society.

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