Decrease of upper critical field with underdoping in cuprate superconductors

TL;DR

This study shows that the upper critical field in underdoped cuprate superconductors decreases with underdoping, indicating that competing stripe order weakens superconductivity rather than phase fluctuations causing the Tc drop.

Contribution

It provides evidence that stripe order competes with superconductivity, leading to a decrease in the upper critical field in underdoped cuprates, resolving previous contradictions.

Findings

Hc2 dips at p=0.11 in Eu-LSCO and YBCO

Superconducting fluctuations decrease with underdoping

Stripe order correlates with weakened superconductivity

Abstract

The transition temperature Tc of cuprate superconductors falls when the doping p is reduced below a certain optimal value. It is unclear whether this fall is due to strong phase fluctuations or to a decrease in the pairing gap. Different interpretations of photoemission data disagree on the evolution of the pairing gap and different estimates of the upper critical field Hc2 are in sharp contradiction. Here we resolve this contradiction by showing that superconducting fluctuations in the underdoped cuprate Eu-LSCO, measured via the Nernst effect, have a characteristic field scale that falls with underdoping. The critical field Hc2 dips at p = 0.11, showing that superconductivity is weak where stripe order is strong. In the archetypal cuprate superconductor YBCO, Hc2 extracted from other measurements has the same doping dependence, also with a minimum at p = 0.11, again where stripe order is present. We conclude that competing states such as stripe order weaken superconductivity and this, rather than phase fluctuations, causes Tc to fall as cuprates become underdoped.