Mottness induced superfluid phase fluctuation with increased density

Abstract

Recent observation of diminishing superfluid phase stiffness upon increasing carrier density in cuprate high-temperature superconductors is unexpected from the quantum density-phase conjugation of superfluidity. Here, through analytic estimation and verified via variational Monte Carlo calculation of an emergent Bose liquid, we point out that Mottness of the underlying carriers can cause a stronger phase fluctuation of the superfluid with increasing carrier density. This effect turns the expected density-increased phase stiffness into a dome shape, in good agreement with the recent observation. Specifically, the effective mass divergence due to "jamming" of the low-energy bosons reproduces the observed nonlinear relation between phase stiffness and transition temperature. Our results suggest a new paradigm, in which unconventional superconductivity in some strongly correlated materials is described by physics of bosonic superfluidity, as opposed to pairing-strength limited Cooper pairing.

Probing a Bose metal via electrons: inescapable non-Fermi liquid scattering and pseudogap physics

“…The Bose metal (employed in this study as a mean field) is obtained as one of the ground states of the EBL model [62]. As the first assumption of the EBL model [59,62,65,[71][72][73], the charge carriers are assumed to be mostly in a tightly bound two-body (bi-fermion) charge-2e state involving the nearest neighboring atomic sites. This assumption is natural below some energy scale (say 150meV) in the presence of various high-energy physics previously proposed for the cuprates, for example, bi-polaronic correlation [74,75], two-dimensional short-range anti-ferromagnetic correlation [76][77][78] and/or cancellation of topological spin current [79,80].…”

“…(An important consequence of this unusual constraint is suppression of the superfluid stiffness in the overdoped region and ultimate destruction of superconductivity around 25%. See [72] for more details. )…”

“…Despite its simplicity, a series of previous studies based on this EBL model have successfully explained many unusual properties of the cuprates. This includes for example, the unusual momentum dependence of the superconducting gap [62], destruction of superconductivity and unusual properties near 5% doping [71], anti-intuitive reduction of superfluid stiffness upon increasing carrier density and the overdoped critical doping [72], the non-superfluid low-temperature pseudogap phase as a Bose metal [59], features in the exotic optical conductivity (mid-infrared and ubiquitous continuum) and transport properties (bad metal, strange metal, and weak insulating behavior) [73], and proportionality between the low-temperature superconducting gap and the normal-state scattering rate [65]. Most essentially, all the disparate semi-quantitative results above were obtained within the same Hamiltonian under a fixed set of parameters in the original work [62].…”

“…For those interested in the cuprates, our successful reproduction of NFL scattering, PG formation, and many related symptoms found in the cuprates leads one to wonder whether the pseudogap regime of the cuprate phase diagram below T * is actually contained within the finite temperature phase of a Bose metal below a higher temperature T BM . In fact, the Bose metal mean field used here directly results from the phase frustrated regime [59,71] of the emergent Bose liquid theory [62,72] of the cuprates, which has been demonstrated to describe many physical properties simultaneously with the same model and a single fixed set of parameters (cf appendix C). Within this EBL model, it is not surprising that the observations from single particle fermion probes such as ARPES and STM are so difficult to explain.…”