Pseudogap in the optical spectra of UPd2Al3

The in-plane optical conductivity of UPd2Al3 was measured at temperatures 2 K<T<300 K in the spectral range from 1-40 cm-1 (0.14-5 meV). As the temperature decreases below 25 K a well pronounced pseudogap of 0.2 meV develops in the optical response. In addition we observed a narrow conductivity peak at zero frequency which at 2 K is less than 1 cm-1 wide but which contained only a fraction of the delocalized carriers. The gap in the electronic excitations might be an inherent feature of the heavy fermion ground state.