Enhancement of superconductivity at the onset of charge-density-wave order in a metal

Abstract

We analyze superconductivity in the cuprates near the onset of an incommensurate charge density wave (CDW) order with momentum Q = (Q, 0)/(0, Q), as observed in the experiments. We first consider a semi-phenomenological charge-fermion model in which hot fermions, separated by Q, attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near CDW transition, Tc = Aḡc, whereḡc is charge-fermion coupling and A is the prefactor which we explicitly compute. We then consider the particular microscopic scenario in which CDW order parameter emerges as a composite field made out of primary spin-density-wave fields. We show that charge-fermion couplingḡc is of order of spin-fermion couplingḡs. As the consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally we analyze the effect of an external magnetic field H. We show that, as H increases, optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with the experiments.

Transformation of the superconducting gap to an insulating pseudogap at a critical hole density in the cuprates

“…3ad. This general trend is consistent with previous reports [16][17][18] . Combining this trend with the appreciable curvatures observed in Fig.…”

“…Our goal is to describe qualitatively the evolution in the physics, in particular the evolution of the 1-particle, 2-particle, and spin-flip excitation energies along the US. Alternative approaches have been put forward in a series of papers by Sachdev and coworkers [17], Chubukov and collaborators [18] and Pepin and coworkers [19] and many others. They start from the band structure Fermi surface and examine the role of U-scattering processes connecting the 8 "hot points", namely the 8 Fermi surface points lying on the US.…”

Remarkable Stability of Charge Density Wave Order inLa1.875Ba0.125CuO4Chen1, Thampy2, Mazzoli3 et al. 2016Phys. Rev. Lett.444472View full textAdd to dashboardCite

“…Conventionally, one expects that the CDW order would compete with superconductivity for electronic density of states near the Fermi level, so the exact nature of the CDW and its relationship with superconductivity has come under great scrutiny. A common scenario in trying to understand the cuprates is that quantum fluctuations near a quantum critical point may drive electron pairing and superconductivity [17][18][19][20][21][22][23], and some have pointed towards CDW [18,20,24,25] or nematic [26][27][28] fluctuations as the relevant modes. An alternative approach proposes that static CDW order and superconductivity may work together, rather than compete, with the potential for a spatially-modulated superconducting wave function [29][30][31][32][33][34].…”

Topological superconducting phases from inversion symmetry breaking order in spin-orbit-coupled systems

“…The full quantum-critical pairing problem is more complicated 23,25,[39][40][41][42][43][44][45] in the sense that (i) bosonic and fermionic self-energies and vertex corrections can have non-analytic behavior and generally cannot be neglected, (ii) the Eliashberg approximation which confines the important fermionic degrees of freedom to the vicinity of the FS is generally invalid, and (iii) the contribution from non-ladder diagrams is generically comparable to that from the ladder diagrams. These issues have been studied and addressed in previous works 24,25,40,42,43,[45][46][47][48] for different quantum critical pairing problems within a large-N f framework, where N f corresponds to the number of fermionic flavors. In particular, it was found that the Eliashberg approximation and the ladder approximation become exact in the N f → ∞ limit.…”