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

TL;DR

The paper proposes a new quantum phase called Quantum Charge Liquid (QCL) to explain anomalous metallic behavior in doped NaCoO$_2$, characterized by a charge-only Fermi sea and a spin-liquid, supported by theoretical and ARPES evidence.

Contribution

It introduces the concept of Quantum Charge Liquid as a novel metallic state with a charge-only Fermi sea and spin-liquid, providing a new framework for understanding NaCoO$_2$ properties.

Findings

QCL explains ARPES Fermi surfaces in NaCoO$_2$.

QCL features a charge-only Fermi sea and a spin-liquid.

Theoretical outline of QCL's microscopic basis.

Abstract

`Quantum Charge Liquid'(QCL), a new phase, is proposed to describe anomalous metallic properties (T < 100 K)of a density 'y' 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' fermi-sea (cFS) of yN charges and a `soft spin-liquid' of yN spin-\half moments forming an `effective lattice' of Heisenberg antiferromagnet. An approximate microscopic theory and some consequences are outlined. Anomalous `Fermi surfaces' seen in ARPES of \ncob and \n7cob matches well with our cFS, rather than a corresponding single band free electron FS.