2024/12/04 by Ar. Abanov, Abanov, Artem, Shang-Shun Zhang +3
Physics and Astronomy · #Rare-earth and actinide compounds #Physics of Superconductivity and Magnetism #Surface and Thin Film Phenomena
paper · pdf · doi:10.48550/arxiv.2412.03698
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 pairing interaction 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) (both infinitesimally small). For superconductivity out of a Fermi liquid, the pairing susceptibility 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 non-singular for other Φ0 (ωm), and (ii) below the instability, it becomes a non-unique 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 multi-critical nature of a superconducting transition in a quantum-critical metal when immediately below the instability an infinite number of superconducting states emerges simultaneously with different amplitudes of the order parameter down to an infinitesimally small one.