Magnetization of underdoped YBa$_2$Cu$_3$O$_{y}$ above the irreversibility field

TL;DR

This study investigates the persistence of weak diamagnetism in underdoped YBa₂Cu₃O₆.₆₇ above the irreversibility field using high-field torque magnetometry, revealing complex suppression behaviors and possible interplay with charge density wave order.

Contribution

It provides detailed high-field magnetization measurements in underdoped YBCO, exploring the nature of superconductivity and competing orders above the irreversibility field.

Findings

Weak diamagnetism persists above the irreversibility field.

Differential susceptibility saturates at high fields (~24 T).

Similar behavior observed in different doping levels and measurement techniques.

Abstract

Torque magnetization measurements on YBa$_2$Cu$_3$O$_{y}$ (YBCO) at doping $y=6.67$($p=0.12$), in DC fields ($B$) up to 33 T and temperatures down to 4.5 K, show that weak diamagnetism persists above the extrapolated irreversibility field $H_{\rm irr} (T=0) \approx 24$ T. The differential susceptibility $dM/dB$, however, is more rapidly suppressed for $B\gtrsim 16$ T than expected from the properties of the low field superconducting state, and saturates at a low value for fields $B \gtrsim 24$ T. In addition, torque measurements on a $p=0.11$ YBCO crystal in pulsed field up to 65 T and temperatures down to 8 K show similar behaviour, with no additional features at higher fields. We discuss several candidate scenarios to explain these observations: (a) superconductivity survives but is heavily suppressed at high field by competition with CDW order; (b) static superconductivity disappears near 24 T and is followed by a region of fluctuating superconductivity, which causes $dM/dB$ to saturate at high field; (c) the stronger 3D ordered CDW that sets in above 15 T may suppress the normal state spin susceptibility sufficiently to give an apparent diamagnetism of the magnitude observed.