Superconducting fluctuations and anomalous diamagnetism in underdoped YBa2Cu3O6+x from magnetization and 63Cu NMR-NQR relaxation measurements

TL;DR

This study investigates superconducting fluctuations and unusual diamagnetism in underdoped YBa2Cu3O6+x, revealing that the anomalous diamagnetism cannot be explained by traditional models and is linked to charge inhomogeneities.

Contribution

The paper provides new insights into the nature of superconducting fluctuations and diamagnetism in underdoped YBCO, highlighting the role of charge inhomogeneities and chain ordering.

Findings

Anomalous diamagnetism is significantly stronger in underdoped YBCO.

Standard anisotropic Ginzburg-Landau theory does not explain the observed diamagnetism.

Charge inhomogeneities and chain ordering are linked to the anomalous diamagnetism.

Abstract

Magnetization and 63Cu NMR-NQR relaxation measurements are used to study the superconducting fluctuations in YBa2Cu3O6+x (YBCO) oriented powders. In optimally doped YBCO the fluctuating negative magnetization M_{fl}(H,T) is rather well described by an anisotropic Ginzburg-Landau (GL) functional and the curves M_{fl}/sqrt{H} cross at Tc. In underdoped YBCO, instead, over a wide temperature range an anomalous diamagnetism is observed, stronger than in the optimally doped compound by about an order of magnitude. The field and temperature dependences of M_{fl} cannot be described either by an anisotropic GL functional or on the basis of scaling arguments. The anomalous diamagnetism is more pronounced in samples with a defined order in the Cu(1)O chains. The 63Cu(2) relaxation rate shows little, if any, field dependence in the vicinity of the transition temperature Tc(H=0). It is argued how the results in the underdoped compounds can be accounted for by the presence of charge inhomogeneities, favoured by chains ordering.