Two-dimensional superconducting fluctuations associated with charge density wave stripes in La$_{1.87}$Sr$_{0.13}$Cu$_{0.99}$Fe$_{0.01}$O$_4$

TL;DR

This study reveals that Fe doping in a cuprate superconductor induces two-dimensional superconducting fluctuations linked to charge density wave stripes, suggesting a possible new form of superconducting order called pair-density-wave.

Contribution

It demonstrates that Fe doping enhances 2D superconducting correlations associated with CDW stripes, providing conditions for the emergence of pair-density-wave order.

Findings

2D superconducting fluctuations are linked to CDW stripe growth.

PDW signatures appear when CDW correlation length exceeds eight lattice units.

Fe doping suppresses T_c but induces novel superconducting correlations.

Abstract

The presence of a small concentration of in-plane Fe dopants in La$_{1.87}$Sr$_{0.13}$Cu$_{0.99}$Fe$_{0.01}$O$_4$ is known to enhance stripe-like spin and charge density wave (SDW and CDW) order, and suppress the superconducting $T_c$. Here, we show that it also induces highly two-dimensional (2D) superconducting correlations that have been argued to be signatures of a new form of superconducting order, so-called pair-density-wave (PDW) order. In addition, using the resonant soft x-ray scattering, we find that the 2D superconducting fluctuation is strongly associated with the CDW stripe. In particular, the PDW signature first appears when the correlation length of the CDW stripe grows over eight times the lattice unit ($\sim$ 8$a$). These results provide critical conditions for the formation of PDW order.