The oxygen isotope effect on the in-plane penetration depth in cuprate superconductors

Abstract

Abstract. Muon-spin rotation (µSR) studies of the oxygen isotope (16 O/ 18 O) effect (OIE) on the in-plane magnetic field penetration depth λ ab in cuprate high-temperature superconductors (HTS) are presented. First, the doping dependence of the OIE on the transition temperature T c in various HTS is briefly discussed. It is observed that different cuprate families show a similar doping dependence of the OIE on T c . Then, bulk µSR, low-energy µSR, and magnetization studies of the total and site-selective OIE on λ ab are described in some detail. A substantial OIE on λ ab was observed in various cuprate families at all doping levels, suggesting that cuprate HTS are nonadiabatic superconductors. The experiments clearly demonstrate that the total OIE on T c and λ ab arise from the oxygen sites within the superconducting CuO 2 planes, demonstrating that the phonon modes involving the movement of planar oxygen are dominantly coupled to the supercarriers. Finally, it is shown that the OIE on T c and λ ab exhibit a relation that appears to be generic for different families of cuprate HTS. The observation of these unusual isotope effects implies that lattice effects play an essential role in cuprate HTS and have to be considered in any realistic model of high-temperature superconductivity.

On the theory of superconductivity in the extended Hubbard model

“…In our theory the strong spin-fluctuation pairing is induced by the kinematic interaction which is absent in the weak correlation limit as in FLEX approximation, and therefore, the EPI plays only a secondary role in the d-wave pairing. A strong EPI in polaronic effects observed in the oxygen isotope effect on the in-plane penetration depth in cuprates [84] may be irrelevant for the pairing mediated by the d-wave partial harmonic of the EPI [85] as confirmed by a weak isotope effect on T c in the optimally doped cuprates.…”

Oxygen Isotope Effects on the Superconducting Transition and Magnetic States Within the Phase Diagram ofY1−xPrxBa2Cu3Khasanov1, Shengelaya2, Castro3 et al. 2008Phys. Rev. Lett.522620View full textAdd to dashboardCite

“…In particular, close to optimal doping the OIE on T c is almost zero [1, 2, 3], while the OIE on λ ab (0) is still substantial [7,8,9,10]. With decreasing doping both OIE's on T c and λ ab (0) increase and, for highly underdoped materials, even exceed the value of the BCS isotope exponent α BCS Tc = 0.5 [2,4,5,7,9,10]. In order to obtain a more global view of cuprate superconductors a detailed study of the isotope dependence of magnetic quantities is needed.…”

“…16 O/ 18 O) effects (OIE's) on various physical quantities, including among others the transition temperature T c , the in-plane magnetic penetration depth λ ab (0), the pseudogap temperature T * , and the spin-glass temperature T g , were observed which cannot be explained by standard BCS theory [1,2,3,4,5,6,7,8,9,10,11,12]. For instance, it was found that the OIE's on T c and λ ab (0) are strongly doping dependent [1,2,3,4,5,6,7,8,9,10].…”

“…For instance, it was found that the OIE's on T c and λ ab (0) are strongly doping dependent [1,2,3,4,5,6,7,8,9,10]. In particular, close to optimal doping the OIE on T c is almost zero [1,2,3], while the OIE on λ ab (0) is still substantial [7,8,9,10].…”

“…As shown in Refs. [4,5,6,7,8] the charge carriers in the 18 O substituted samples are heavier and, consequently, less mobile than in 16 O substituted samples. The recent studies of Hücker et al [18] clearly demonstrate that increasing the hole mobility in La 2−x Sr x CuO 4 rapidly suppresses the antiferromagnetic ordering temperature T N .…”