Oxygen isotope effect (OIE) studies have been used to probe the extent of electron-phonon interactions in the pairing mechanism [1] and in the pseudogap formation [2] in cuprate superconductors. In this talk, we present a new OIE study of Pr-doped YBa₂Cu₃O_7-δ (YPrBCO), which is the only member of the RBCO (R = rare earth) family where its superconductivity can be systematically suppressed (by Pr-doping) without changing its oxygen content. Recently, YPrBCO has also been shown to exhibit incommensurate charge-density-waves (CDWs) all the way to the insulating Mott limit [3]. This study uses epitaxial YPrBCO thin films grown by pulsed laser deposition to maximize doping and isotope homogeneity. The samples were characterized using X-ray diffraction, X-ray reflectometry, scanning transmission electron microscopy (STEM), and scanning tunning microscopy. The substitution of ¹⁶O by ¹⁸O was done by gas-phase diffusion and confirmed using Raman spectroscopy and STEM. Electrical transport measurements and resonant X-ray scattering were used to determine the superconducting critical temperature (T_c), the pseudogap onset temperature (T^*), and the CDW onset temperature (T_CDW) respectively. Isotope shifts of T_CDW are used to probe the extent of electron-phonon interactions in the charge order, and correlations between the isotope shifts of T_c, T^* and T_CDW are used to determine the degree of interaction between the respective electronic orders. Our results are discussed in the context of the pseudogap and its relationship to the superconductivity and charge order in oxygen-underdoped YBCO and YPrBCO.

[1] G. Zhao et al., PRB 51 16487(R) (1995)

[2] D. Temperano et al., PRL 84 1990 (1999)

[3] M. Kang et al., PNAS 120 e2302099120 (2023)