Revisiting the electronic phase diagram of YBa2Cu3Oy via temperature derivative of in-plane resistivity

TL;DR

This study uses the temperature derivative of in-plane resistivity to refine the YBa2Cu3Oy phase diagram, revealing detailed insights into superconducting fluctuations, resistivity behavior, and transport property correlations across doping levels.

Contribution

It introduces the use of d ho_{ab}/dT to better identify superconducting fluctuations and resistivity regimes in YBCO, providing a more detailed phase diagram than previous methods.

Findings

Tf marks the onset of superconducting fluctuations, similar to Tc.

Resistivity shows a T^2 dependence in a specific doping range.

Transport properties like Hall coefficient and thermopower are correlated with resistivity derivatives.

Abstract

We have re-examined the temperature-doping (T-p) phase diagram of YBa2Cu3Oy (YBCO) to address several issues therein by using the temperature derivative of in-plane resistivity, d\{rho}ab/dT. For p less than about 0.15, a temperature Tf has been defined to mark the onset of an upturn in d\{rho}ab/dT at T>Tc, which, in light of prior studies on another cuprate La2-xSrxCuO4, is attributed to the onset of superconducting fluctuations in normal state. The Tf exhibits a doping dependence similar to Tc, and the interval between Tf and Tc is about 5-30 K across the underdoped regime, showing agreement with a variety of other measurements to probe a restricted temperature range of superconducting fluctuations. Above Tf, the d\{rho}ab/dT increases linearly as T increases up to a value denoted as T2, which is about half the T* and falls roughly in parallel with T* as p rises up to about 0.13, indicating a prominent T^2-dependent \{rho}ab in this T-p region. The d\{rho}ab/dT helps reveal that, at Tf<T<T2, the \{rho}ab also involves an insulating-like component for p<0.08, or a T-linear component for p>0.10-0.11, thereby leaving a narrow window of doping for \{rho}ab to show a pure T^2 dependence. As T increases further, the d\{rho}ab/dT reaches a local maximum at a temperature T_R, signifying the known curvature change (inflection point) in \{rho}ab. With the derivatives, it is illustrated that, in the vicinity of T_R, the in-plane Hall coefficient R_H and thermopower Sab of YBCO display curvature changes as well, suggesting a correlation of the three transport properties. It is also found that the dSab/dT shows the onset of an upturn at a temperature coinciding with the Tf, which, backing the identification of Tf with the onset of superconducting fluctuations, demonstrates further the virtue of using the temperature derivative to unveil information helpful for the study of high-Tc cuprates.