Revealing the pseudogap in Sr3(Ru0.985Fe0.015)2 O7 by optical spectroscopy

We report resistivity, magnetization, and optical spectroscopy study on single-crystal sample of Sr3(Ru0.985Fe0.015)2O7. An upturn is observed in resistivity at about 30 K. Below 30 K, the dip in resistivity R(ω), the suppression in scattering rate 1/τ(ω), the peaklike feature in optical conductivity σ1(ω), and the remainder of spectral weight all suggest the formation of a pseudogap. In addition, one phonon peak at about 600cm-1 is distinguished at all temperatures, which has asymmetric line shape. Such asymmetric line shape can be fit by a Fano function, and the resulting Fano factor 1/q2 and linewidth γ show significant increases below 30 K, giving further evidence for the formation of a pseudogap, which might originate from the partial k-space gap opening due to density wave instability.