Quantum Charge Liquid - a new metallic state in 2 dimensions ? Application to Na$_{0.7}$CoO$_2$ family

Abstract

`Quantum Charge Liquid&#39;(QCL), a new phase, is proposed to describe anomalous metallic properties (T < 100 K)of a density &#39;y&#39; of doped holes with strong coulomb repulsions, in a band insulator NaCoO$_2$ with N sites. This phase, a quantum melted charge order, is characterized by a `charge only&#39; fermi-sea (cFS) of yN charges and a `soft spin-liquid&#39; of yN spin-\half moments forming an `effective lattice&#39; of Heisenberg antiferromagnet. An approximate microscopic theory and some consequences are outlined. Anomalous `Fermi surfaces&#39; seen in ARPES of \ncob and \n7cob matches well with our cFS, rather than a corresponding single band free electron FS.