Spin susceptibility of charge-ordered YBa₂Cu₃O y across the upper critical field

• Published in: Proceedings of the National Academy of Sciences - PNAS 2017-12, Vol.114 (50), p.13148-13153
• Main Authors: Zhou, Rui, Hirata, Michihiro, Wu, Tao, Vinograd, Igor, Mayaffre, Hadrien, Krämer, Steffen, Reyes, Arneil P., Kuhns, Philip L., Liang, Ruixing, Hardy, W. N., Bonn, D. A., Julien, Marc-Henri
• Format: Article
• Language: English
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1711445114

The value of the upper critical field H c2, a fundamental characteristic of the superconducting state, has been subject to strong controversy in high-Tc copper oxides. Since the issue has been tackled almost exclusively by macroscopic techniques so far, there is a clear need for local-probe measurements. Here, we use 17O NMR to measure the spin susceptibility χ spin of the CuO₂ planes at low temperature in charge-ordered YBa₂Cu₃O y . We find that χ spin increases (most likely linearly) with magnetic field H and saturates above field values ranging from 20 T to 40 T. This result is consistent with the lowest H c2 values claimed previously and with the interpretation that the charge density wave (CDW) reduces H c2 in underdoped YBa₂Cu₃O y . Furthermore, the absence of marked deviation in χ spin(H) at the onset of long-range CDW order indicates that this H c2 reduction and the Fermi-surface reconstruction are primarily rooted in the short-range CDW order already present in zero field, not in the field-induced long-range CDW order. Above H c2, the relatively low values of χ spin at T = 2 K show that the pseudogap is a ground-state property, independent of the superconducting gap.