Multiscale quantum criticality: Pomeranchuk instability in isotropic metals

TL;DR

This paper investigates the complex quantum critical behavior of a Pomeranchuk instability in 2D isotropic metals, revealing multiple dynamical scales and their effects on thermodynamics and phase diagram through renormalization group analysis.

Contribution

It introduces a multi-scale quantum critical framework for Pomeranchuk instability, highlighting the interplay of coupled modes with different dynamical exponents and their impact on physical properties.

Findings

Multiple dynamical scales influence quantum critical behavior.

Logarithmic singularities are treated via renormalization group.

Finite temperature crossover is significantly affected by scale coexistence.

Abstract

As a paradigmatic example of multi-scale quantum criticality, we consider the Pomeranchuk instability of an isotropic Fermi liquid in two spatial dimensions, d=2. The corresponding Ginzburg-Landau theory for the quadrupolar fluctuations of the Fermi surface consists of two coupled modes, critical at the same point, and characterized by different dynamical exponents: one being ballistic with dynamical exponent z=2 and the other one is Landau-damped with z=3, thus giving rise to multiple dynamical scales. We find that at temperature T=0, the ballistic mode governs the low-energy structure of the theory as it possesses the smaller effective dimension d+z. Its self-interaction leads to logarithmic singularities, which we treat with the help of the renormalization group. At finite temperature, the coexistence of two different dynamical scales gives rise to a modified quantum-to-classical crossover. It extends over a parametrically large regime with intricate interactions of quantum and classical fluctuations leading to a universal T-dependence of the correlation length independent of the interaction amplitude. The multiple scales are also reflected in the phase diagram and in the critical thermodynamics. In particular, we find that the latter cannot be interpreted in terms of only a single dynamical exponent: whereas, e.g., the critical specific heat is determined by the z=3 mode, the critical compressibility is found to be dominated by the z=2 fluctuations.