Angle-resolved photoemission study of Zn-doped PrBa₂Cu₄O₈: Possible observation of single-particle spectral function for a Tomonaga-Luttinger liquid

We have studied the electronic structure of metallic Cu-O double chains in Zn-doped PrBa₂Cu₄O₈ (Pr124) using angle-resolved photoemission spectroscopy. The single-particle spectral function of Zn-doped Pr124 is compatible with a power-law spectral function expected for a Tomonaga-Luttinger liquid. This is in contrast to the fact that the photoemission spectrum of pure Pr124 shows a Fermi step and can be interpreted as a Fermi liquid realized in coupled metallic chains. The exponent α is estimated to be 0.6±0,1 that is one of the smallest values among those obtained for various one-dimensional metals.