Nernst effect in the electron-doped cuprate superconductor PCCO: Superconducting fluctuations, upper critical field Hc2, and the origin of the Tc dome

TL;DR

This study measures the Nernst effect in electron-doped cuprate PCCO across various dopings, revealing that superconducting fluctuations and the upper critical field Hc2 are closely linked to the Tc dome and are explained by Gaussian fluctuations, not phase fluctuations.

Contribution

It demonstrates that Gaussian superconducting fluctuations account for the Nernst effect and the Tc dome in PCCO, challenging the role of phase fluctuations in underdoped cuprates.

Findings

H* peaks follow Hc2* ln(T/Tc) in all dopings.

Hc2* tracks the Tc dome, indicating phase competition.

Gaussian fluctuations explain the Nernst signal without vortex-like excitations.

Abstract

The Nernst effect was measured in the electron-doped cuprate superconductor Pr2-xCexCuO4 (PCCO) at four concentrations, from underdoped (x=0.13) to overdoped (x=0.17), for a wide range of temperatures above the critical temperature Tc. A magnetic field H up to 15 T was used to reliably access the normal-state quasiparticle contribution to the Nernst signal, Nqp, which is subtracted from the total signal, N, to obtain the superconducting contribution, Nsc. As a function of H, Nsc peaks at a field H* whose temperature dependence obeys Hc2* ln(T/Tc), as it does in a conventional superconductor like Nb1-xSix. The doping dependence of the characteristic field scale Hc2* - shown to be closely related to the upper critical field Hc2 - tracks the dome-like dependence of Tc, showing that superconductivity is weakened below the quantum critical point where the Fermi surface is reconstructed, presumably by the onset of antiferromagnetic order. Our data at all dopings are quantitatively consistent with the theory of Gaussian superconducting fluctuations, eliminating the need to invoke unusual vortex-like excitations above Tc, and ruling out phase fluctuations as the mechanism for the fall of Tc with underdoping. We compare the properties of PCCO with those of hole-doped cuprates and conclude that the domes of Tc and Hc2 vs doping in the latter materials are also controlled predominantly by phase competition rather than phase fluctuations.