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 system(1,2) collapses at higher dimensions, it has been proposed to be relevant to enigmatic problems in condensed matter physics including the normal state of cuprate superconductors(3-5), unconventional metals(6,7) and quantum criticality(8,9). Here we investigate the electronic structure of quasi-2D eta-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 eta-Mo4O11 materializes the crossed LL phase(10-12) 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.