Non-BCS behavior of the pairing susceptibility near the onset of superconductivity in a quantum-critical metal

Artem Abanov; Shang-Shun Zhang; Andrey V. Chubukov

doi:10.1103/PhysRevB.111.075157

← Back to search

Non-BCS behavior of the pairing susceptibility near the onset of superconductivity in a quantum-critical metal

Artem Abanov, Shang-Shun Zhang, Andrey V. Chubukov

DOI 10.1103/PhysRevB.111.075157 · Physical Review B

T1

Active bibliographic source — not scientific approval

Bibliographic access preserves source history; it does not approve extracted materials or validate reported claims. Review warnings on each occurrence separately.

Abstract

We analyze the dynamical pairing susceptibility χpp(ωm) at T=0 in a quantum-critical metal, where superconductivity emerges out of a non-Fermi-liquid ground state once the attraction exceeds a certain threshold. We obtain χpp(ωm) as the ratio of the fully dressed dynamical pairing vertex Φ(ωm) and the bare Φ0(ωm). For superconductivity out of a Fermi liquid, the pairing susceptibility in the normal state is positive above Tc, diverges at Tc, and becomes negative below it. For superconductivity out of a non-Fermi-liquid, the behavior of χpp(ωm) is different in two aspects: (i) it diverges at the onset of pairing at T=0 only for a certain subclass of bare Φ0(ωm) and remains nonsingular for other Φ0(ωm), and (ii) below the instability, it becomes a nonunique function of a continuous parameter ϕ for an arbitrary Φ0(ωm). The susceptibility is negative in some range of ϕ and diverges at the boundary of this range. We argue that this behavior of the susceptibility reflects a multicritical nature of a superconducting transition in a quantum-critical metal, where, immediately below the instability, an infinite number of superconducting states emerges simultaneously, exhibiting different amplitudes of the order parameter down to an infinitesimally small one.