Asymmetric Conductivity, Pseudogap and Violations of Time and Charge Symmetries

Abstract

In this Chapter we show that tunneling differential conductivity (or resistivity) is a sensitive tool to experimentally test the non-Fermi liquid (NFL) behavior of strongly correlated Fermi systems. In the case of common metals the Landau Fermi liquid (LFL) theory demonstrates that the differential conductivity is a symmetric function of bias voltage V. This is because the particle-hole symmetry is conserved in LFL state. When a strongly correlated Fermi system approaches the topological fermion condensation quantum phase transition, its LFL properties disappear so that the particle-hole symmetry breaks making the differential tunneling conductivity an asymmetric function of V. This asymmetry can be observed when a strongly correlated metal is in its normal, superconducting or pseudogap states. We show that the asymmetric part of the dynamic conductance does not depend on temperature provided that the metal is in its superconducting or pseudogap states. In normal state the asymmetric part diminishes at rising temperatures. Under the application of magnetic field the metal transits to the LFL state and the differential tunneling conductivity becomes a symmetric function of V. These findings are in good agreement with experimental observations on graphene.