Torque magnetization measurements on YBa2Cu3Oy (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 Hirr(T=0)≈24 T. The differential susceptibility dM/dB, however, is more rapidly suppressed for B≳16 T than expected from the properties of the low field superconducting state, and saturates at a low value for fields B≳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 behavior, with no additional features at higher fields. We offer two candidate scenarios to explain these observations: (a) superconductivity survives but is heavily suppressed at high field by competition with charge-density-wave (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. The diamagnetic signal observed above 50 T for the p=0.11 crystal at 40 K and below may be caused by changes in the normal state susceptibility rather than bulk or fluctuating superconductivity. There will be orbital (Landau) diamagnetism from electron pockets and possibly a reduction in spin susceptibility caused by the stronger three-dimensional ordered CDW.
Physical Review B
Yu JF, Ramshaw BJ, Kokanović I, et al. Magnetization of underdoped YBa2Cu3Oy above the irreversibility field. Physical Review B. 2015;92(18). doi:10.1103/physrevb.92.180509
Yu, J. F., Ramshaw, B. J., Kokanović, I., Modic, K. A., Harrison, N., Day, J., … Cooper, J. R. (2015). Magnetization of underdoped YBa2Cu3Oy above the irreversibility field. Physical Review B. APS. https://doi.org/10.1103/physrevb.92.180509
Yu, Jing Fei, B. J. Ramshaw, I. Kokanović, Kimberly A Modic, N. Harrison, James Day, Ruixing Liang, et al. “Magnetization of Underdoped YBa2Cu3Oy above the Irreversibility Field.” Physical Review B. APS, 2015. https://doi.org/10.1103/physrevb.92.180509.
J. F. Yu et al., “Magnetization of underdoped YBa2Cu3Oy above the irreversibility field,” Physical Review B, vol. 92, no. 18. APS, 2015.
Yu JF, Ramshaw BJ, Kokanović I, Modic KA, Harrison N, Day J, Liang R, Hardy WN, Bonn DA, McCollam A, Julian SR, Cooper JR. 2015. Magnetization of underdoped YBa2Cu3Oy above the irreversibility field. Physical Review B. 92(18), 180509.
Yu, Jing Fei, et al. “Magnetization of Underdoped YBa2Cu3Oy above the Irreversibility Field.” Physical Review B, vol. 92, no. 18, 180509, APS, 2015, doi:10.1103/physrevb.92.180509.