FFLO strange metal and quantum criticality in two dimensions: theory and application to organic superconductors

Abstract

Increasing the spin imbalance in superconductors can spatially modulate the gap by forming Cooper pairs with finite momentum. For large imbalances compared to the Fermi energy, the inhomogeneous FFLO superconductor ultimately becomes a normal metal. There is mounting experimental evidence for this scenario in 2D organic superconductors in large in-plane magnetic fields; this is complemented by ongoing efforts to realize this scenario in coupled tubes of atomic Fermi gases with spin imbalance. Yet, a theory for the phase transition from a metal to an FFLO superconductor has not been developed so far and the universality class has remained unknown. Here we propose and analyze a spin imbalance driven quantum critical point between a 2D metal and an FFLO phase in anisotropic electron systems. We derive the effective action for electrons and bosonic FFLO pairs at this quantum phase transition. Using this action, we predict non-Fermi liquid behavior and the absence of quasi-particles at a discrete set of hot spots on the Fermi surfaces. This results in strange power-laws in thermodynamics and response functions, which are testable with existing experimental set-ups on 2D organic superconductors and may also serve as signatures of the elusive FFLO phase itself. The proposed universality class is distinct from previously known quantum critical metals and, because its critical fluctuations appear already in the pairing channel, a promising candidate for naked metallic quantum criticality over extended temperature ranges.

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References in corpus (17)

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• The FFLO state in the one-dimensional attractive Hubbard model and its fingerprint in the spatial noise correlations
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• Non-Fermi liquid behavior at the onset of incommensurate 2k_F charge or spin density wave order in two dimensions
• On the superconducting state of the organic conductor $(TMTSF{)}_{2}Cl{O}_4$

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• Renormalization theory for the Fulde-Ferrell-Larkin-Ovchinnikov states at $T>0$
• Fluctuation effects at the onset of $2{\mathbf{k}}_{\mathbf{F}}$ density wave order with one pair of hot spots in two-dimensional metals
• Non-Fermi-Liquid Behavior from Cavity Electromagnetic Vacuum Fluctuations at the Superradiant Transition
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• Evolution of an attractive polarized Fermi gas: From a Fermi liquid of polarons to a non-Fermi liquid at the Fulde-Ferrell-Larkin-Ovchinnikov quantum critical point
• Reentrant Fulde-Ferrell-Larkin-Ovchinnikov superfluidity in the honeycomb lattice
• Effective potential and quantum criticality for imbalanced Fermi mixtures
• Stability of the Fulde-Ferrell-Larkin-Ovchinnikov states in anisotropic systems and critical behavior at thermal $m$-axial Lifshitz points
• Diffusion Monte Carlo study of a spin-imbalanced two-dimensional Fermi gas with attractive interactions
• Damping of the Anderson-Bogolyubov mode by spin and mass imbalance in Fermi mixtures
• Renormalization Group Flows in Non-Relativistic Holographic Effective Field Theories