Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta

TL;DR

This study investigates how the superconducting transition temperature in HgBa2CuO4+δ relaxes over time under pressure, revealing weak relaxation effects and nonlinear pressure dependence linked to structural or electronic changes.

Contribution

It provides new high-pressure data on HgBa2CuO4+δ, demonstrating relaxation effects and nonlinear T_c behavior, highlighting differences from other cuprates.

Findings

Weak relaxation effects with activation energy ~0.8-0.9 eV.

Nonlinear T_c dependence on pressure, indicating structural/electronic changes.

Activation volume of +11 ± 5 cm³ under pressure.

Abstract

In previous studies on a number of under- and overdoped high temperature superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta}, the transition temperature T_c has been found to change with time in a manner which depends on the sample's detailed temperature and pressure history. This relaxation behavior in T_c is believed to originate from rearrangements within the oxygen sublattice. In the present high-pressure studies on HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation effects in strongly under- and overdoped samples ($T_c\simeq 40 - 50 K$) with an activation energy $E_{A}(1 bar) \simeq 0.8 - 0.9 eV$. For overdoped HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of +11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an anomalous result for high-T_c superconductors in the present pressure range, giving evidence for a change in the electronic and/or structural properties near 0.4 GPa.