Crossed Luttinger liquid hidden in a quasi-two-dimensional material

Although the concept of the Luttinger liquid (LL) describing a one-dimensional (1D) interacting fermion system1,2 collapses at higher dimensions, it has been proposed to be relevant to enigmatic problems in condensed matter physics including the normal state of cuprate superconductors3–5, unconventional metals6,7 and quantum criticality8,9. Here we investigate the electronic structure of quasi-2D η-Mo4O11, a charge-density wave material, using high-resolution angle-resolved photoemission spectroscopy and ab initio calculations. We show a prototypical LL behaviour originating from the crossed quasi-1D chain arrays hidden in the quasi-2D crystal structure. Our results suggest that η-Mo4O11 materializes the crossed LL phase10–12 in its normal state, where the orthogonal orbital components substantially reduce the coupling between intersecting quasi-1D chains and therefore maintain the essential properties of the LL. Our finding not only presents a realization of a 2D LL, but also provides a new angle to understand non-Fermi liquid behaviour in other 2D and 3D quantum materials.