nonFermiliquid

Non-Fermi liquid refers to electronic states of matter in which the low-energy excitations cannot be described by the conventional Landau Fermi liquid framework. In a Fermi liquid, quasiparticles with long lifetimes exist near the Fermi surface and physical properties follow characteristic temperature dependences; non-Fermi liquids violate these expectations due to strong interactions, fluctuations, or criticality.

Key signatures include a resistivity that varies linearly with temperature at low temperatures rather than quadratically; a specific heat coefficient that remains enhanced or shows non-quadratic temperature dependence; anomalous magnetic susceptibility; and a self-energy with non-quadratic frequency or temperature dependence, often without well-defined long-lived quasiparticles. Optical and other spectroscopic probes may reveal unusual exponents or scaling behavior that deviate from Fermi-liquid expectations.

Common origins include proximity to quantum critical points, where fluctuations of an order parameter persist over wide energy scales; strong electronic correlations, Kondo breakdown, or coupling to emergent gauge fields; and in some one- or two-dimensional systems where non-Fermi-liquid behavior is intrinsic rather than emergent from criticality. Disorder and frustration can also play a role in promoting non-Fermi-liquid-like responses.

Prominent experimental occurrences appear in certain heavy-fermion materials, such as CeCu6−xAux and YbRh2Si2, as well as in the normal state of some high-temperature superconductors near optimal doping and in some iron-based superconductors. Theoretical descriptions include extended dynamical mean-field theory, quantum critical frameworks (Hertz-Mills-Moriya type), marginal Fermi liquid concepts, and holographic approaches that seek to model strongly coupled non-Fermi-liquid states.